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Effect of blanching and drying temperatures on starch-related physicochemical properties, bioactive components and antioxidant activities of yam flours
Accepted Manuscript Effect of blanching and drying temperatures on starch-related physicochemical properties, bioactive components and antioxidant activities of yam flours Xuetao Chen, Jun Lu, Xia Li, Ying Wang, Jing Miao, Xinhui Mao, Chengcheng Zhao, Wenyuan Gao PII:
S0023-6438(17)30279-7
DOI:
10.1016/j.lwt.2017.04.058
Reference:
YFSTL 6196
To appear in:
LWT - Food Science and Technology
Received Date: 28 January 2017 Revised Date:
15 April 2017
Accepted Date: 17 April 2017
Please cite this article as: Chen, X., Lu, J., Li, X., Wang, Y., Miao, J., Mao, X., Zhao, C., Gao, W., Effect of blanching and drying temperatures on starch-related physicochemical properties, bioactive components and antioxidant activities of yam flours, LWT - Food Science and Technology (2017), doi: 10.1016/j.lwt.2017.04.058. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Effect of blanching and drying temperatures on starch-related physicochemical
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properties, bioactive components and antioxidant activities of yam flours Xuetao Chen a1, Jun Lu a1, Xia Li a∗, Ying Wang a, Jing Miao a, Xinhui Mao a,
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Chengcheng Zhao a, Wenyuan Gao a∗
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a
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Pharmaceutical Science and Technology, Tianjin University, Tianjin 300072, China
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The author contributed equally to this article
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Tianjin Key Laboratory for Modern Drug Delivery and High-Efficiency, School of
∗
Corresponding author: Dr. Xia Li, Tel: +86-22-8740 1895. E-mail address: [email protected]
∗
Corresponding author: Prof. Dr. Wenyuan Gao, Tel/Fax: +86-22-8740 1895 E-mail address: [email protected] 1
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ABSTRACT: The effects of blanching (in boiling water for 1min) and different hot air drying
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temperatures (40ºC, 60ºC and 80ºC) on the polyphenol oxidase (PPO), peroxidase
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(POD) and antioxidant activities, main bioactive components, as well as the
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starch-related physicochemical properties of yam flours were studied. The results of
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PPO and POD activities, and total flavone and total soluble polyphenol contents
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showed that blanching was effective to inhibiting enzymatic browning of yams, and
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the substrate of enzymatic browning reaction may be mainly flavonoid ingredients.
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The sample of H-40 had higher allantoin and total soluble polyphenol content,
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stronger DPPH scavenging activity and reducing power. From the results of scanning
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electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared
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(FT-IR), the blanching yams was found contain partly gelatinized starch granules, and
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had lower crystallinity. The H-40 and H-80 samples had higher RS contents and lower
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GI values. Furthermore, the protein and soluble amylose contents, solubility and
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swelling power at 90ºC of the blanching yams were lower than those of the yams
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without blanching. We can effectively apply these flours in various products based on
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their characteristics.
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Keywords: Yam flour; Blanching；Drying temperature; Starch; Antioxidant capacity
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1. Introduction Yams, the tuber of Dioscorea opposita Thunb., have been considered as a
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superior Chinese herb to improve functions of stomach and spleen (SPC, 2015), as
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well as the fourth major root crop in the world after cassava, potatoes and sweet
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potatoes (Akinoso and Olatoye, 2013). The major active components in yams are
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allantoin, phenolic compounds, and others (Niu et al., 2010; Muzac-Tucker et al.,
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1993). Nonetheless, starch is the predominant fraction of yams, making up
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approximately 75-84% of the total biomass.
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Fresh yams are difficult to store and are susceptible to deterioration during
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storage. Dried yam slices and flours are the main products in the market, which can be
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easily stored in the long term and conveniently consumed in these forms. Our
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previous studies (Chen et al., 2017) have found that hot air drying (HAD) at 60ºC
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would be a better method for yam drying. Several studies have reported the effect of
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different drying temperatures on the physio-chemical and starch-related properties.
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(Correia and Beirão-da-Costa, 2012; Attanasio et al., 2004; Falade et al., 2007).
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Therefore, study on the effects of different drying temperatures on the properties of
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yam flours is very necessary. In addition to this, fresh-cut processing, such as peeling
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and cutting, may accelerates physiological deterioration, which leads to yam
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browning. Browning, decline in the nutritional quality and overall visual quality of
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yams, severely decreases its market potential. This browning known as enzymatic
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browning reactions (Bhandari and Kawabata, 2004) is attributed to the oxidation of
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phenolic compounds by polyphenol oxidase (PPO) and peroxidase (POD). The
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ACCEPTED MANUSCRIPT phenolic compounds were oxidized to quinones, in turn these were polymerized to
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form brown pigments (Queiroz et al., 2008). Barrett et al. (1991) reported the
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condition of mechanical injury may result in changes in cell membrane permeability
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and release of either stored substrates from the vacuole or bound enzymes from
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organelles, which may be involved in enzymatic browning.
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Some measures have been used to inhibit enzymatic browning of yam during
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processing. These approaches include sulfur fumigation (Jiang et al., 2013), soaking
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in chemicals (Krishnan et al., 2010), and electrolyzed water (Jia et al., 2015).
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However, these measures more or less had chemical residues, to which consumers
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don't want. Birch et al. reported that the most of the enzyme kept in hot water of
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100ºC for 1 min would be inactivation (Birch et al., 2012; Desrosier et al., 1977).
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Blanching is an effective and commonly used method, which has relatively low costs.
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In this study, according to the previous research (Chen et al., 2017) and practical
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production, we chose 60ºC, 40ºC (lower than 60ºC) and 80ºC (higher than 60ºC) for
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yams drying, and determined the effects of blanching and different drying
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temperatures on starch-related properties, and bioactive components' contents, as well
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as antioxidant capacity. Finally, aiming toward an effective utilization of these flours
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in various food products.
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2. Materials and methods
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2.1. The preparation of dried yam flours
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Fresh Chinese yam (Dioscorea opposita) was collected from Wen town, Jiaozuo
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city, Henan Province in China. The yam tubers were washed, peeled, then cut into 4
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slices were divided into 3 subgroups, and they were dried in hot air drying oven
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(DL-101-1S, Tianjin Central Lab Electric Furnace Co., Ltd., China) with air speed
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0.15 m/s, at 40ºC for 10h (H-40), 60ºC for 6h (H-60), and 80ºC for 3 h (H-80),
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respectively. Another group of slices were blanched in a boiling water bath (about
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100ºC) for 1 min, the blanched yam slices were divided into three subgroups, and
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dried in hot air drying oven with air speed 0.15 m/s, at 40ºC for 10h (BH-40), 60ºC
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for 6h (BH-60), and 80ºC for 3 h (BH-80), respectively.
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The dried yam samples were ground in a blender (WND-200, Lanxi Weinengda
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Electric Co., Ltd. Zhejiang, China), and sieved through a screen (75±4.1 µm) to obtain
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yam flours.
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2.2. Moisture, protein, and total starch content determination
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The moisture content of the yam flour was analyzed according to SPC (2015).
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The protein contents of the yam flours were determined according to Bradford’s dye
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binding method, using bovine serum albumin (BSA) as standard (Bradford, 1976).
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The total starch content of the yam flour was determined using enzymatic hydrolysis,
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described by Jiang et al. (2010).
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2.3. Apparent amylose content and soluble amylose content
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The apparent amylose contents and the soluble amylose contents of yam flour
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was estimated by using the method of Chen et al. (2016).
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2.4. Water-binding capacity (WBC)
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Water-binding capacity (WBC) of the yam flour was determined according to the 5
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previous reported method (Chen et al., 2017).
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2.5. Swelling power (SP) and solubility (SOL) Solubility and the swelling power were measured according to a method
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described by Chen et al. (2017).
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2.6. Scanning electron microscopy (SEM)
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The morphological features of the yam flours were observed with an
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environmental scanning electron microscope (SEM, Shimadzu SS-550). The dried
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samples were mounted on a metal stub, coated with gold powder to make the sample
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conductive, and images were then taken with an accelerating voltage of 1.9 kV.
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2.7. X-ray diffraction (XRD)
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X-ray diffraction patterns of the yam flours were analyzed according to the previous reported method (Chen et al., 2017).
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2.8. Fourier transform infrared spectroscopy (FT-IR)
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Fourier transform infrared spectroscopy observed according to the previous reported method (Chen et al., 2017).
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2.9. In vitro digestibility
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The in vitro digestibilities of the yam flours were determined according to the
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procedure of Chen et al. (2017).
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2.10. Polyphenol oxidase (PPO) and peroxidase (POD) activities
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The PPO and POD activities were determined by the method described by Jia et
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al. (2015) with some modifications. Extraction solution was 2 g polyvinyl
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polypyrolidone (PVPP) mixed with 100mL sodium phosphate buffer (0.2 mol/L, pH 6
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total of 2 mL of extraction solution was added to the tube, stirred up the extraction
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solution for 1 min. The mixture was centrifuged at 12000x g for 5 min at 4 °C. This
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extraction and collection was repeated three times. The supernatant was collected for
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determinations of the PPO and POD activity.
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The substrate was 1.5 mL of 20 mg/mL catechol. Other reaction mixtures
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included 1.5 mL of 50 mmol/L phosphate buffer (pH 7.0), and 0.2 mL of the enzyme
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solution. For the blank sample, 0.2 mL of phosphate buffer was used instead of 0.2
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mL enzyme solution. The PPO activity was determined as the amount of the enzyme
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catalyzing a linear increase of 0.001 absorbance per minute per gram yam flour at 410
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nm.
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The substrate was 25 mmol/L guaiacol and 25 mmol/L hydrogen peroxide
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dissolved in 0.05 mol/L sodium phosphate buffer (pH 7.0). The reactant contained 2.8
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mL substrate and 0.2 mL enzyme solution. For the blank sample, 0.2 mL of phosphate
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buffer was used instead of 0.2 mL enzyme solution. The POD activity unit (U) was
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defined as a 0.001 linear increase in absorbance per minute per gram fresh weight at
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470 nm.
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2.11. Preparation of methanol sample extracts for determination of soluble phenolic,
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flavonoids, and allantoin contents, as well as antioxidant activity assays
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Yam flours (4 g) were placed into test tubes. A total of 15 mL of 80 mL/100mL
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methanol was added to each tube, and the tubes were sonicated for 30 min at room
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temperature. After centrifugation at 3000x g for 5 min, the supernatant was collected. 7
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extract was concentrated by vacuum rotary evaporation at 50°C, dissolved in 80
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mL/100mL methanol to yield 10 mL of total solution, which was used for
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determination soluble phenolic, flavonoids, and allantoin contents, as well as reducing
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power. The methanolic yam extract (400 mg/mL) was diluted to the following
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concentrations for the DPPH radical scavenging test: 10, 20, 30, 40, 50, 60 and 70
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mg/mL.
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2.12. Determination of total soluble polyphenol and total flavonoid content
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Determinations of the total soluble polyphenol and total flavonoid contents of
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samples were performed using the methods previously reported (Chen et al., 2017).
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2.13. Determination of allantoin content
Determination of allantoin content according the method described in the
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previously report (Chen et al., 2017).
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2.14. Determination of antioxidant activity Antioxidant activity of yam flours evaluated by DPPH radical scavenging and
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reducing power assay. The methods of DPPH radical scavenging and reducing power
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test were previously report (Chen et al., 2017).
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2.15. Statistical analysis
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All determinations were performed in triplicate, and the data were expressed as
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the mean values ± SD. Analysis of variance was performed to calculate significant
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differences by Student-Newman-Keuls (SNK) and least -significant difference (LSD)
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post hoc test for univariate comparison (P ≤ 0.05). The data were statistically 8
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analyzed using the IBM SPSS Statistics 20 (SPSS Inc. Chicago, IL, USA).
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3. Results and discussion
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3.1. Total starch, amylose, protein, and WBC The moisture content of yam flours ranged from 5.85 g/100g to 12.66 g/100g,
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and the blanching samples showed higher moisture content than samples without
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blanching at same drying temperature (Table 1). This phenomenon may be due to the
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fact that the blanching led to starch gelatinization, and during the subsequent drying
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process a resistant film layer was formed on the surface of the samples, which
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reduced water transfer (Xiao et al., 2012).
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The total starch content was from 67.08 g/100g to 77.52 g/100g, and the
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blanching samples presented lower total starch content values than samples dried at
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temperatures of 40ºC and 60ºC (Table 1). The results showed that the total starch
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content was decreased with drying temperature increasing. These phenomena may be
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explained by the result that the thermal treatments caused the formation of modified
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starch, which is not detectable by the enzymatic test (Voragen, 1998).
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Concerning protein content in both samples (Table 1), the blanching samples
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present lower protein content values, and the protein content decreased with drying
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temperature increasing. These differences among protein content could be due to
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denaturation or changes in solubility during blanching and heating, which may have
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caused the proteins to leach out into the water (Danso-Boateng, 2013).
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The apparent amylose contents of blanching samples (10.31 g/100g - 12.66
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g/100g) were higher than the samples without blanching dried at the same temperature 9
ACCEPTED MANUSCRIPT (8.62 g/100g - 11.08 g/100g). The soluble amylose content of blanching samples (3.00
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g/100g - 5.57 g/100g) was lower than the without blanching samples (7.17 g/100g -
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7.50 g/100g). The H-60 sample had higher soluble amylose content among all
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samples, and the soluble amylose content of BH-60 sample was higher among the
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blanching samples. The reason of these phenomena possibly was the increase
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combined action of enzymes on starch during the yam drying process (Correia et al.,
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2009). These enzymes mainly include α-amylase, β-amylase, glucoamylase, and
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pullulanase, which are optimum active at temperature between 55ºC and 60ºC
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(Correia and Beirão-da-Costa, 2012). The insoluble amylose content ranged from 1.27
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g/100g to 9.66 g/100g. It has been reported that the insoluble amylose was related to
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the long chain B of the amylopectin molecule (Takeda et al., 1987).The insoluble
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amylose contents of blanching samples were higher than those without blanching
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samples. This phenomenon may be attributed to the thermal degradation of the
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amylopectin (Dharmaraj and Malleshi, 2011), and the dissociation and reaggregation
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of
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amylose-amylose, amylose-amylopectin chains and amylose-lipids during blanching
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process (Raja and Sindhu, 2000).
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The WBC of all samples ranged from 188.02 g/100g to 257.15 g/100g, and the
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blanching samples dried at temperatures of 40ºC and 60ºC present higher WBC values
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than others, while the BH-80 sample had lower WBC value. The WBC value of
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samples without blanching increased with the temperature increasing. These
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phenomena may be due to the fact that higher temperature produced in blanching and 10
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2014). Rayas-Duarte et al. (1998) reported that the degree of starch gelatinization and
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fragmentation may be considered among the main factors affecting the WBC.
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3.2. Swelling power and solubility
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The swelling powers and solubilities of all the yam flours at temperatures in the
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range between 50ºC to 90ºC are presented in Table 2. The swelling power and
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solubility of each sample showed a continuous increase with increasing drying
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temperature. The extent of this increase was more pronounced at temperatures beyond
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70ºC. The swelling powers of blanching yam flours were lower than those samples
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without blanching at 80ºC and 90ºC. The solubility of each blanching sample was
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lower than the sample without blanching dried at the same temperature. The increased
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insoluble amylose contents in blanching samples (Table 1), which may facilitate
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additional interaction between amylose-amylose and/or amylose-amylopectin, as well
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as formed amylose-lipid complexes, may be responsible for decreasing of the swelling
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powers and solubilities of blanching samples (Gunaratne and Hoover, 2002). Tester
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and Morrison (1990) comparatively studied on the non-waxy and waxy maize starch,
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and reported that swelling is primarily a property of amylopectin, while amylose acts
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as an inhibitor of swelling. Cooke and Gidley (1992) have suggested that the forces
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holding the granule together are mainly at the double helical level and that the starch
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‘crystallinity’ functions as a means of achieving dense packing rather than as primary
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provider of structure. These imply that the lower swelling powers in blanching
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samples could also be due to the decreased of granular stabilities, resulting from the
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thermal degradation of the amylopectin, which led to the unraveling of double helices.
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3.3. Scanning electron microscopy (SEM) The SEM of all the yam flours is shown in Fig. 1. The starch granules of samples
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without blanching presented oval and spherical shaped with size ranging from 8 to
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35µm. There was no significant difference of morphology among samples dried with
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different temperature. However, major differences were found in chestnut flours dried
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at different temperatures, the gelatinization phenomena is quicker in starch granules
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from chestnut flours drying at high temperature (Correia et al., 2012). The granules of
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blanching samples presented different shapes and sizes, which partly have gelatinized.
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The ungelatinized granules showed the similar shapes and sizes to granules of
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samples without blanching. Some gelatinized granules become large masses, which
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showed characteristic block and irregular structure, and had a cranny and rough
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surface. The results may be due to the fact that partial gelatinization and subsequent
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retrogradation of starch which appeared to be bonded together by binders like water
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and gelatinized starch (Kuttigounder et al., 2011; Dhanalakshmi & Bhattacharya,
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2014).
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possibly due to the decreased moisture (binder of reassociated starch). The most
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gelatinized granules of BH-40 sample become large masses (100-140 µm), which
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showed characteristic block and irregular structure, and had a cranny and rough
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surface. There were large masses and small fragments in the BH-60 sample. The most
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gelatinized granules of BH-80 sample were small fragments, which had large range of
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size (30-100 µm), irregular structure, and a cranny and rough surface.
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3.4. X-ray diffraction (XRD) The samples dried by different temperatures, both of blanching and without
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blanching, shown A - type XRD patterns with reflection intensities at 2θ values of
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15.0º, 17.0º, 17.8º, 19.5º and 23º (Fig. 2). The relative crystallinities of blanching
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samples (9.35%-14.28%) were lower than those the samples without blanching
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(16.26%-23.88%), and the relative crystallinity decreased with increasing drying
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temperature (Table 3). The differences in relative crystallinity among different yam
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flours probably represent differences in the orientational order parameter of the
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amylopectin double helices and average chain length of amylopectin, as well as mole
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percentage of the short chain fraction of amylopectin (Gunaratne and Hoover, 2002;
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Waigh et al., 2000). From the SEM of blanching samples (Fig.1), we found that the
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partly starch granules gelatinized. Waigh et al. (2000) reported that there were two
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transformations (crystalline smectic to isotropic/nematic transition at lower
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temperatures and helix-coil transition at higher temperatures) in starch during
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gelatinization, which led to the lower crystallinities.
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3.5. Fourier transform infrared (FT - IR)
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The FT - IR spectra of starches have been shown to be sensitive to changes in
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structure on a molecular level (short-range order), such as changes in chain
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conformation and double helical order (van Soest et al., 1995). The absorption region
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from 800 to 1200 cm-1 of deconvoluted FT - IR spectra of the studied yam flours are
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presented in Fig. 3. This region of the IR spectra is characterized by these main modes
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with maximum absorbance at 995, 1022, 1035 and 1047 cm-1 (van Soest et al., 1995). 13
ACCEPTED MANUSCRIPT The absorption bands at 1047 and 1035 cm-1 are associated with the crystalline and
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short-range order of starch, the absorption band at 1022 cm-1 is associated with the
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amorphous structures of starch, and the band at 995 cm-1 is ascribed to a single-helix
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crystalline structure environment (Jiang et al., 2014; van Soest et al., 1995). The ratios
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of peak intensities at 1047/1022 (R1047/1022) and 995/1022 (R995/1022) are used to
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compare the degrees of crystallinity and molecular order of the starches. The ratio of
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peak intensities at 1047/1035 (R1047/1035) expresses the amount of ordered starch,
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which is very sensitive to water content (Mutungi et al., 2011; van Soest et al., 1995).
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The values of R1047/1022, R1047/1035 and R995/1022 were calculated (Table 3). The R1047/1022
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values ranged from 0.9117 for BH-80 sample to 0.9759 for BH-40 sample, and the
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R995/1022 values ranged from 0.9510 for the BH-40 sample to 1.1017 for the H-40
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sample, which had different trend with crystallinity. The similar results reported in the
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literature of Lan et al. (2016), and the results may be due to the fact that crystallinity
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from XRD is a measure of long-range order, which would not necessarily be present
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when short-range order exists. The R995/1022 values ranged from 0.9510 for the BH-40
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sample to 1.1017 for the H-40 sample, and the R1047/1035 values ranged from 0.9807
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for the BH-80 sample to 1.0063 for the H-40 sample in line with the same observed
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trend in crystallinity.
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3.6. In vitro digestibility
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The in vitro digestibilities of starches from the yam flours were evaluated by
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determining the RDS, SDS and RS contents (Table 3). The RS contents of blanching
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samples (36.20-46.98%) were lower than those samples without blanching 14
ACCEPTED MANUSCRIPT (55.44-62.63%). The reasons for this was that blanching led to greater degree of
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starch gelatinization, irregular shaped starch granules, cranny and rough surface,
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lower protein content, lower degree of crystallinity, and thermal degradation of the
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amylopectin. These factors may have made it easier for enzyme to attack the chains,
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which have been reported in the literature (Dhital et al., 2010; Chung and Liu, 2012).
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The samples of H-80 (50.18%) and H-40 (54.72%) had a low GI (GI ≤ 55), H-60
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(64.41%) and BH-80 (66.25%) had an intermediate GI (GI, 56-69), BH-40 (69.81%)
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and BH-60 (81.76%) had a high GI (GI ≥ 70) (Moraes et al., 2015).
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3.7. Polyphenol oxidase (PPO) and Peroxidase (POD) activities
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The effect of blanching and different temperatures on PPO and POD activities of
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yam flours is shown in Table 4. The PPO activities of blanching samples (0.004-0.007
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AU/g•min) were significant lower than those without blanching samples (0.015-0.028
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AU/g•min). The POD activities of yam flours had the same trend with PPO activities.
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The POD activities of blanching samples was lower (0.0003-0.0007 AU/g•min),
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while those of the samples without blanching was higher (0.0011-0.0020 AU/g•min).
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The result is consistent with Landymore’s (2001) report, which find that the enzymes
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would instantaneously lose activity at moist heat temperatures near the boiling point
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of water. The PPO and POD activities decreased with increasing temperature. The
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phenomenon may be due to the fact that PPO and POD is sensitive to thermal, and
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had maximum activity at 30ºC and 35ºC, respectively (Zhang and Shao, 2015).
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Landymore (2001) reported that an increase of 10ºC, the inactivation rate will
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increase sixty-four-fold.
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3.8. Bioactive components in the yam flours The observed allantoin, total flavone, and total soluble phenolic contents are
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shown in Table 4. The allantoin content of the H-60 (0.155g/100g) was the highest,
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followed by H-40 (0.149 g/100g), BH-60 (0.095 g/100g), BH-80 (0.078 g/100g), H-80
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(0.075 g/100g), and BH-40 (0.066 g/100g). The allantoin was synthesized in roots
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mainly via purine degradation process, which involved in some enzymes (mainly,
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xanthine oxidase, uricase and allantoinase) (Thomas and Schrader, 1981). Therefore,
320
the lower allantoin content in those samples (BH-60, BH-80, H-80, and BH-40) may
321
be due to the activity of enzyme, which was inhibited during blanching and high
322
temperature heating processes.
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Total soluble phenolic contents ranged from 0.57 mg CE/g for BH-80 sample to
324
1.05 mg CE/g for H-40 sample, and total soluble phenolic content of H-40 sample
325
much higher than others. The total soluble phenolic contents decreased with
326
temperatures increasing, and total soluble phenolic contents of BH-40 and BH-80
327
samples significant decreased compared with those of H-40 and H-80 samples,
328
respectively. Those phenomena may be due to thermal degradation (autoxidation or
329
breakdown) during blanching and high temperature heating processes, and diffusion
330
or/and leaching into the water during blanching (Jaiswal et al., 2012; Gonçalves et al.,
331
2010). The total flavones contents of blanching samples (0.50-0.60 mg RE/g) were
332
higher than those samples without blanching (0.35-0.49 mg RE/g). The significant
333
negative correlation was found between total flavones contents and PPO activities (r =
334
-0.861, P ≤ 0.01, Table 5), POD activities (r = -0.736, P ≤ 0.01, Table 5). This
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16
ACCEPTED MANUSCRIPT 335
phenomenon suggested that the substrate of enzymatic browning reaction was mainly
336
flavonoid ingredients.
337
3.9. Antioxidant capacities of the flours The antioxidant capacities of yam flours were evaluated by a DPPH radical assay
339
and a reducing power assay (Table 4). The H-40 sample showed strong (EC50 value
340
was 87.00 mg/mL) DPPH radical scavenging activity, followed by BH-60 (EC50 value
341
was 106.45 mg/mL), BH-40 (EC50 value was 111.10 mg/mL), H-60 (EC50 value was
342
142.50 mg/mL), BH-80 (EC50 value was 158.15 mg/mL), and H-80 (EC50 value was
343
189.15 mg/mL). The EC50 value of the DPPH radical scavenging activity was
344
negatively correlated with total flavonoid content (r = -0.821, P ≤ 0.01, Table 5). The
345
result suggested that total flavonoid content is largely responsible for the DPPH
346
radical scavenging activity.
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The reducing powers of the H-40 (147.76 µmol AC/g dw) was the highest,
348
followed by BH-80 (128.40 µmol AC/g dw) and H-60 (126.50 µmol AC/g dw),
349
BH-60 (112.96 µmol AC/g dw), BH-40 (103.32 µmol AC/g dw), and H-80 (93.39
350
µmol AC/g dw). Reducing power was statistically determined to be positively
351
correlated to total soluble phenolic content (r = 0.684, P ≤ 0.05, Table 5). The result
352
suggested that total soluble phenolic content is largely responsible for the reducing
353
power.
354
4. Conclusions
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The blanching pre-treatment at boiling water (about 100ºC) for 1min, was
356
effective to inhibiting enzymatic browning of yams, and the substrate of enzymatic 17
ACCEPTED MANUSCRIPT browning reaction was mainly flavonoid ingredients. The sample of H-40, had higher
358
allantoin and total soluble polyphenol content, stronger DPPH scavenging activity and
359
reducing power, which is an important source of functional foods that are increasingly
360
popular today. From the perspective of the starch-related properties, the partly starch
361
granules of blanching samples was gelatinization, and the crystallinity was lower. The
362
H-40 and H-80 samples, which had higher RS contents and lower GI values, are ideal
363
for preparing hypoglycemic and lipid-lowering functional foods. What’s more, the
364
protein and soluble amylose contents, solubility and swelling power at 90ºC of the
365
blanching yams were lower than those of the yams without blanching. Based on their
366
characteristics, these flours can be effectively applied in various products. In order to
367
fully understand the effect of blanching and hot air drying, further characterization of
368
the phenolic compounds as future work needs to be done.
369
Conflict of interest
370
The authors have declared no conflict of interest.
371
Acknowledgments
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This work was financially supported by Special Scientific Research of Chinese
373
Medicine Industry (201307008) from the State Administration of Traditional Chinese
374
Medicine, Science and Technology Program of China (NO. 2014FY111100).
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ACCEPTED MANUSCRIPT References
376
Akinoso, R., & Olatoye, K. K. (2013). Energy utilization and conservation in
377
instant-pounded yam flour production. International Food Research Journal, 20,
378
575-579.
RI PT
375
Attanasio, G., Cinquanta, L., Albanese, D., & Di Matteo, M. (2004). Effects of drying
380
temperatures on physico-chemical properties of dried and rehydrated chestnuts
381
(Castanea sativa). Food Chemistry, 88, 583-590.
SC
379
Barrett, D. M., Lee, C. Y., & Liu, F. W. (1991). Changes in the activity and subcellular
383
distribution of ppo in ‘delicious’ apples during controlled atmosphere storage.
384
Journal of Food Biochemistry, 15, 185-199.
386
Birch, G. G., Blakebrough, N., & Parker, K. J. (2012). Enzymes and food processing. Springer Science & Business Media.
TE D
385
M AN U
382
Bhandari, M. R., & Kawabata, J. (2004). Organic acid, phenolic content and
388
antioxidant activity of wild yam (Dioscorea spp.) tubers of Nepal. Food
389
Chemistry, 88, 163-168.
391 392
Bradford, M. M., 1976. A rapid and sensitive method for the quantitation of
AC C
390
EP
387
microgram quantities of protein utilizing the principle of protein-dye binding. Analytical Biochemistry, 72, 248-254.
393
Chen, X., Li, X., Mao, X., Huang, H., Miao, J., & Gao, W. (2016). Study on the
394
effects of different drying methods on physicochemical properties, structure, and
395
in vitro digestibility of Fritillaria thunbergii Miq. (Zhebeimu) flours. Food and
396
Bioproducts Processing, 98, 266-274. 19
ACCEPTED MANUSCRIPT Chen, X., Li, X., Mao, X., Huang, H., Wang, T., Qu, Z., ... & Gao, W. (2017). Effects
398
of drying processes on starch-related physicochemical properties, bioactive
399
components and antioxidant properties of yam flours. Food Chemistry, 224,
400
224-232.
RI PT
397
Chiu, C. S., Deng, J. S., Chang, H. Y., Chen, Y. C., Lee, M. M., Hou, W. C., Lee, C. Y.,
402
Huange, S. S., & Huang, G. J. (2013). Antioxidant and anti-inflammatory
403
properties of taiwanese yam (Dioscorea japonica Thunb. Var. pseudojaponica
404
(Hayata) Yamam.) and its reference compounds. Food Chemistry, 141,
405
1087-1096.
M AN U
SC
401
Chung, H. J., & Liu, Q. (2012). Physicochemical properties and in vitro digestibility
407
of flour and starch from pea (Pisum sativum L.) cultivars. International Journal
408
of Biological Macromolecules, 50, 131-137.
TE D
406
Cooke, D., & Gidley, M. J. (1992). Loss of crystalline and molecular order during
410
starch gelatinisation: origin of the enthalpic transition. Carbohydrate Research,
411
227, 103-112.
413 414
Correia, P., Leitão, A., & Beirão-da-Costa, M. L. (2009). The effect of drying
AC C
412
EP
409
temperatures on morphological and chemical properties of dried chestnuts flours. Journal of Food Engineering, 90(3), 325-332.
415
Correia, P., & Beirão-da-Costa, M. L. (2012). Effect of drying temperatures on
416
starch-related functional and thermal properties of chestnut flours. Food and
417
Bioproducts Processing, 90, 284-294.
418
Danso-Boateng, E. (2013). Effect of drying methods on nutrient quality of Basil 20
ACCEPTED MANUSCRIPT 419
(Ocimum viride) leaves cultivated in Ghana. International Food Research
420
Journal, 20, 1569-1573.
422 423 424
Desrosier, N. W., & Desrosier, J. N. (1977). The technology of food preservation (No. Ed. 4). AVI Publishing Company, Inc..
RI PT
421
Dhital, S., Shrestha, A. K., & Gidley, M. J. (2010). Effect of cryo-milling on starches: Functionality and digestibility. Food Hydrocolloids, 24, 152-163.
Dharmaraj, U., & Malleshi, N. G. (2011). Changes in carbohydrates, proteins and
426
lipids of finger millet after hydrothermal processing. LWT-Food Science and
427
Technology,, 44, 1636-1642.
M AN U
SC
425
Dhanalakshmi, K., & Bhattacharya, S. (2014). Agglomeration of turmeric powder and
429
its effect on physico-chemical and microstructural characteristics. Journal of
430
Food Engineering, 120, 124-134.
TE D
428
Falade, K. O., Olurin, T. O., Ike, E. A., & Aworh, O. C. (2007). Effect of pretreatment
432
and temperature on air-drying of Dioscorea alata and Dioscorea rotundata slices.
433
Journal of Food Engineering, 80, 1002-1010.
435 436
Gonçalves, E. M., Pinheiro, J., Abreu, M., Brandão, T. R. S., & Silva, C. L. (2010).
AC C
434
EP
431
Carrot (Daucus carota L.) peroxidase inactivation, phenolic content and physical changes kinetics due to blanching. Journal of Food Engineering, 97, 574-581.
437
Gunaratne, A., & Hoover, R. (2002). Effect of heat-moisture treatment on the
438
structure and physicochemical properties of tuber and root starches.
439
Carbohydrate Polymers, 49, 425-437.
440
Jaiswal, A. K., Gupta, S., & Abu-Ghannam, N. (2012). Kinetic evaluation of colour, 21
ACCEPTED MANUSCRIPT 441
texture, polyphenols and antioxidant capacity of Irish York cabbage after
442
blanching treatment. Food Chemistry, 131, 63-72. Jia, G. L., Shi, J. Y., Song, Z. H., & Li, F. D. (2015). Prevention of enzymatic
444
browning of Chinese yam (Dioscorea spp.) using electrolyzed oxidizing water.
445
Journal of Food Science, 80, C718-C728.
RI PT
443
Jiang, H., Jane, J. L., Acevedo, D., Green, A., Shinn, G., Schrenker,D., Srichuwong,
447
S., Campbell, M., Wu, Y., 2010. Variations in starch physicochemical properties
448
from a generation-means analysis study using amylomaize V and VII parents.
449
Journal of Agricultural and Food Chemistry, 58, 5633-5639.
M AN U
SC
446
Jiang, Q., Gao, W., Shi, Y., Li, X., Wang, H., Huang, L., & Xiao, P. (2013).
451
Physicochemical properties and in vitro digestion of starches from different
452
Dioscorea plants. Food Hydrocolloids, 32, 432-439.
TE D
450
Jiang, X., Huang, L. F., Zheng, S. H., & Chen, S. L. (2013). Sulfur fumigation, a
454
better or worse choice in preservation of traditional Chinese medicine?
455
Phytomedicine, 20, 97-105.
457 458 459
Jiang, Q., Gao, W., Li, X., Man, S., Shi, Y., Yang, Y., ... & Liu, C. (2014).
AC C
456
EP
453
Comparative susceptibilities to alkali-treatment of A-, B-and C-type starches of Dioscorea zingiberensis, Dioscorea persimilis and Dioscorea opposita. Food Hydrocolloids, 39, 286-294.
460
Krishnan, J. G., Padmaja, G., Moorthy, S. N., Suja, G., & Sajeev, M. S. (2010). Effect
461
of pre-soaking treatments on the nutritional profile and browning index of sweet
462
potato and yam flours. Innovative Food Science & Emerging Technologies, 11, 22
ACCEPTED MANUSCRIPT 463
387-393. Kuttigounder, D., Lingamallu, J. R., & Bhattacharya, S. (2011). Turmeric powder and
465
starch: selected physical, physicochemical, and microstructural properties.
466
Journal of Food Science, 76, C1284-C1291.
RI PT
464
Landymore, C. L. (2001). Evaluation of protein utilisation of vacuum microwave, air,
468
and freeze-dried Euphausia pacifica in a rat model (Doctoral dissertation,
469
University of British Columbia).
SC
467
Lan, X., Xie, S., Wu, J., Xie, F., Liu, X., & Wang, Z. (2016). Thermal and enzymatic
471
degradation induced ultrastructure changes in canna starch: Further insights into
472
short-range and long-range structural orders. Food Hydrocolloids, 58, 335-342.
M AN U
470
Liyana-Pathirana, C. M., & Shahidi, F. (2007). Antioxidant and free radical
474
scavenging activities of whole wheat and milling fractions. Food Chemistry, 101,
475
1151-1157.
TE D
473
Moraes, É. A., da Silva Marineli, R., Lenquiste, S. A., Steel, C. J., de Menezes, C. B.,
477
Queiroz, V. A. V., & Júnior, M. R. M. (2015). Sorghum flour fractions:
478
Correlations among polysaccharides, phenolic compounds, antioxidant activity
AC C
479
EP
476
and glycemic index. Food Chemistry, 180, 116-123.
480
Muzac-Tucker, I., Asemota, H. N., & Ahmad, M. H. (1993). Biochemical composition
481
and storage of Jamaican yams (Dioscorea sp). Journal of the Science of Food
482
and Agriculture, 62, 219-224.
483
Mutungi, C., Onyango, C., Doert, T., Paasch, S., Thiele, S., Machill, S., Jaros, D., &
484
Rohm, H. (2011). Long- and short-range structural changes of recrystallised 23
ACCEPTED MANUSCRIPT 485
cassava starch subjected to in vitro digestion. Food Hydrocolloids, 25, 477-485. Niu, C. S., Chen, W., Wu, H. T., Cheng, K. C., Wen, Y. J., Lin, K. C., & Cheng, J. T.
487
(2010). Decrease of plasma glucose by allantoin, an active principle of yam
488
(Dioscorea spp.), in streptozotocin-induced diabetic rats. Journal of Agricultural
489
and Food Chemistry, 58, 12031-12035.
RI PT
486
Queiroz, C., Mendes Lopes, M. L., Fialho, E., & Valente-Mesquita, V. L. (2008).
491
Polyphenol oxidase: characteristics and mechanisms of browning control. Food
492
Reviews International, 24, 361-375.
494
M AN U
493
SC
490
Raja, M. K., & Sindhu, P. (2000). Properties of Steam-Treated Arrowroot (Maranta arundinacea) Starch. Starch‐Stärke, 52, 471-476.
Rayas-Duarte, P., Majewska, K., & Doetkott, C. (1998). Effect of extrusion process
496
parameters on the quality of buckwheat flour mixes 1. Cereal Chemistry, 75,
497
338-345.
500 501 502 503 504 505 506
China Medical Science and Technology Press, Beijing.
EP
499
State Pharmacopoeia Committee, 2015. Pharmacopeia of People’s Republic of China.
Tacer-Caba, Z., Nilufer-Erdil, D., Boyacioglu, M. H., & Ng, P. K. (2014). Evaluating
AC C
498
TE D
495
the effects of amylose and Concord grape extract powder substitution on physicochemical properties of wheat flour extrudates produced at different temperatures. Food Chemistry, 157, 476-484.
Takeda, Y., Hizukuri, S., & Juliano, B. O. (1987). Structures of rice amylopectins with low and high affinities for iodine. Carbohydrate Research, 168, 79-88. Tester, R. F., & Morrison, W. R. (1990). Swelling and gelatinization of cereal starches. 24
ACCEPTED MANUSCRIPT 507 508 509
I. Effects of amylopectin, amylose, and lipids. Cereal Chemistry, 67, 551-557. Thomas, R. J., & Schrader, L. E. (1981). Ureide metabolism in higher plants. Phytochemistry, 20, 361-371. van Soest, J. J., Tournois, H., de Wit, D., & Vliegenthart, J. F. (1995). Short-range
511
structure in (partially) crystalline potato starch determined with attenuated total
512
reflectance Fourier-transform IR spectroscopy. Carbohydrate Research, 279,
513
201-214.
515
SC
Voragen, A. G. (1998). Technological aspects of functional food-related carbohydrates.
M AN U
514
RI PT
510
Trends in Food Science & Technology, 9, 328-335.
Waigh, T. A., Gidley, M. J., Komanshek, B. U., & Donald, A. M. (2000). The phase
517
transformations in starch during gelatinisation: a liquid crystalline approach.
518
Carbohydrate Research, 328, 165-176.
TE D
516
Wang, S. J., Yu, J. L., Gao, W, Y., Pang, J. P., Liu, H, Y., & Yu, J, G. (2007). Granule
520
structural changes in native Chinese Yam (Dioscorea opposita Thunb var. Anguo)
521
starch during acid hydrolysis. Carbohydrate Polymers, 69, 286-292.
523 524
Xia, X., Cao, J., Zheng, Y., Wang, Q., & Xiao, J. (2014). Flavonoid concentrations
AC C
522
EP
519
and bioactivity of flavonoid extracts from 19 species of ferns from China. Industrial Crops and Products, 58, 91-98.
525
Xiao, H. W., Yao, X. D., Lin, H., Yang, W. X., Meng, J. S., & Gao, Z. J. (2012). Effect
526
of SSB (superheated steam blanching) time and drying temperature on hot air
527
impingement drying kinetics and quality attributes of yam slices. Journal of
528
Food Process Engineering, 35, 370-390. 25
ACCEPTED MANUSCRIPT
TE D
M AN U
SC
RI PT
and the role in browning of loquat fruit. Journal of Food Science, 33, 109-117.
EP
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Zhang, X., & Shao, X. (2015). Characterisation of polyphenol oxidase and peroxidase
AC C
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Fig. 1.
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Scannjng electron microphs (SEM) of yam flours. H-40, Hot air drying at 40ºC;
534
BH-40, Hot air drying at 40ºC after blanching; H-60, Hot air drying at 60ºC; BH-60,
535
Hot air drying at 60ºC after blanching; H-80, Hot air drying at 80ºC; BH-80, Hot air
536
drying at 80ºC after blanching.
537
Fig. 2.
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X-ray diffraction (XRD) of yam flours. a, Hot air drying at 40ºC; b, Hot air drying at
539
40ºC after blanching; c, Hot air drying at 60ºC; d, Hot air drying at 60ºC after
540
blanching; e, Hot air drying at 80ºC; f, Hot air drying at 80ºC after blanching.
541
Fig. 3.
542
Deconvoluted FT - IR spectra of yam flours. a, Hot air drying at 40ºC; b, Hot air
543
drying at 40ºC after blanching; c, Hot air drying at 60ºC; d, Hot air drying at 60ºC
544
after blanching; e, Hot air drying at 80ºC; f, Hot air drying at 80ºC after blanching.
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Moisture, protein, TS, AAM, SAM, IAM and WBC of yam flours
Sample
Protein
Moisture (g/100g)
(g/100g) c
77.52±0.48
(g/100g)
d
8.62±0.00
IAM
(g/100g) a
7.35±0.01
WBC
(g/100g) e
1.27±0.01
(g/100g) a
188.02±2.22a
H-40
12.29±0.39
BH-40
14.56±0.25d
0.44±0.00b
71.22±0.79b
10.31±0.00c
3.21±0.00b
7.10±0.00e
243.78±4.40c
H-60
9.69±0.00 b
1.86±0.02d
73.82±0.60c
11.08±0.01d
7.50±0.00f
3.58±0.01c
199.62±1.34a
BH-60
12.66±0.27c
0.20±0.00a
67.08±0.67a
11.89±0.01e
5.57±0.01c
6.32±0.01d
257.15±3.85d
H-80
5.86±0.68a
1.82±0.01c
67.96±0.56a
9.99±0.01b
7.17±0.01d
2.82±0.01b
219.04±7.99b
BH-80
9.36±0.58 b
0.20±0.00a
67.42±0.27a
12.66±0.01f
3.00±0.00a
9.66±0.01f
189.90±1.37a
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2.57±0.02
e
SAM
AAM
TS (g/100g)
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Values are means ± SD. Means with different letters in the same column differ significantly (P ≤ 0.05). TS, total
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starch; AAM, apparent amylose; SAM, soluble amylose; IAM, insoluble amylose; WBC, water-binding capacity;
H-40, Hot air drying at 40ºC; BH-40, Hot air drying at 40ºC after blanching; H-60, Hot air drying at 60ºC; BH-60,
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Hot air drying at 60ºC after blanching; H-80, Hot air drying at 80ºC; BH-80, Hot air drying at 80ºC after blanching
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Table 2
Swelling power and solubility at different temperatures of yam flours Swelling power (g/g) at different temperatures 50 ºC
60 ºC a
70 ºC
80 ºC
18.82±0.18
50 ºC d
60 ºC
70 ºC
30.15±0.80 c
6.64±0.07b
6.41±0.07b
11.39±0.04bc
12.19±0.14b
16.64±0.49d
15.23±0.10b
16.27±0.27b
18.05±0.08b
22.03±0.04b
ab
b
12.17±0.01
c
d
b
e
e
e
48.83±1.04e
BH-60
6.02±0.15b
5.19±0.09ab
7.35±0.15b
7.61±0.43a
15.02±0.43c
H-80
4.34±0.19a
5.20±0.22ab
5.23±0.19a
14.21±0.09c
19.43±0.53d
BH-80
5.00±0.08 ab
5.03±0.03ab
7.76±0.20b
8.79±0.27 ab
10.60±0.08a
13.10±0.13
28.51±0.49
30.51±0.41
20.29±0.10
90 ºC c
a
18.25±0.15
19.42±0.11
80 ºC c
5.41±0.09ab 4.11±0.07
18.22±0.18
c
BH-40 H-60
16.37±0.28
d
3.97±0.23
7.74±0.05
11.61±0.30
90 ºC bc
H-40
5.14±0.28
4.32±0.14
a
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3.67±0.16
a
Solubility (g/100g) at different temperatures
SC
Sample
43.15±0.65
11.81±0.19a
11.25±0.21a
13.49±0.43a
15.68±0.43a
24.30±0.16a
16.08±0.31d
22.49±0.69d
20.78±0.03d
23.66±0.34d
33.02±0.26d
14.57±0.16c
15.51±0.18b
16.74±0.11b
18.62±0.06b
25.29±0.16b
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Values are means ± SD. Means with different letters in the same column differ significantly (P ≤ 0.05). H-40: Hot air drying at 40ºC; BH-40, Hot air drying at 40ºC after blanching; H-60, Hot air
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drying at 60ºC; BH-60, Hot air drying at 60ºC after blanching; H-80, Hot air drying at 80ºC; BH-80, Hot air drying at 80ºC after blanching.
ACCEPTED MANUSCRIPT
Infrared ratios of absorbance, relative crystallinity, RDS, SDS, and RS contents, GI and HI of yam flours IR ratio of absorbance RDS (%)
1.006316
23.88±2.65d
1.63±0.26b
0.951015
0.992825
14.28±0.84bc
0.952427
1.081862
1.001982
22.35±1.45d
BH-60
0.94113
0.960983
0.988167
12.10±1.02ab
H-80
0.949624
1.063488
0.997881
16.26±1.43c
BH-80
0.911749
0.983158
0.980698
9.35±0.38a
R995/1022
R1047/1035
H-40
0.957253
1.101653
BH-40
0.97586
H-60
SDS (%)
RS (%)
GI (%)
HI (%)
13.25±0.26b
62.63±0.48d
54.72±0.59b
27.34±1.07b
7.03±0.00d
17.21±0.50d
46.98±0.79b
69.81±0.60e
54.83±1.09e
2.16±0.00c
16.22±0.51c
55.44±2.02c
64.41±0.95c
44.98±1.74c
13.54±0.26e
17.34±0.00d
36.20±0.67a
81.76±0.67f
76.60±1.23f
0.72±0.00a
5.35±0.00a
61.89±1.97d
50.18±0.45a
19.07±0.81a
2.20±0.00c
19.58±0.26e
45.64±1.69b
66.25±0.48d
48.34±0.87d
SC
Relative crystallinity (%) R1047/1022
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Sample
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Table 3
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Values are means ± SD. Means with different letters in the same column differ significantly (P ≤ 0.05). RDS, Rapidly digestible starch; SDS, Slowly digestible starch; RS, Resistant starch; GI, Glycemic index; HI, Hydrolysis index; H-40, Hot air drying at 40ºC; BH-40, Hot air drying at 40ºC after blanching; H-60, Hot air drying at 60ºC; BH-60, Hot air drying at 60ºC after blanching;
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H-80, Hot air drying at 80ºC; BH-80, Hot air drying at 80ºC after blanching.
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Table 4
PPOPOD activities, allantoin, total flavones and total polyphenols contents, as well as antioxidant capacity of yam flours Total flavone
Total soluble polyphenol
DPPH scavenging activity
Reducing power
(mg RE/g)
(mg CE/g)
(EC50, mg/mL)
(µmol AC/g dw)
0.149±0.002d
0.49±0.00c
1.05±0.00e
87.00±0.96a
BH-40
0.066±0.003a
0.60±0.00f
0.70±0.00d
H-60
0.155±0.000e
0.38±0.00b
0.68±0.01c
BH-60
0.095±0.000c
0.58±0.00e
0.68±0.00 c
H-80
0.075±0.003b
0.35±0.00a
0.60±0.01b
BH-80
0.078±0.003b
0.50±0.00d
0.57±0.01a
H-40
PPO（AU/g•min）
POD（AU/g•min）
147.76±1.53e
0.028±0.003d
0.0020±0.0000d
111.10±0.80b
103.32±0.92b
0.004±0.000a
0.0007±0.0000b
142.50±0.82c
126.50±1.33d
0.024±0.001c
0.0012±0.0000c
106.45±0.87b
112.96±2.87c
0.005±0.000a
0.0007±0.0000b
189.15±0.18e
93.39±0.53a
0.015±0.001b
0.0011±0.0002c
158.15±0.27d
128.40±1.31d
0.007±0.000a
0.0003±0.0000a
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Allantoin (g/100g)
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Values are means ± SD. Means with different letters in the same column differ significantly (P ≤ 0.05). PPO, Polyphenol oxidase; POD, Peroxidase; H-40, Hot air drying at 40ºC; BH-40, Hot air
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drying at 40ºC after blanching; H-60, Hot air drying at 60ºC; BH-60, Hot air drying at 60ºC after blanching; H-80, Hot air drying at 80ºC; BH-80, Hot air drying at 80ºC after blanching.
ACCEPTED MANUSCRIPT Table 5
Pearson correlation coefficients for the relationship of TF, TSP, PPO, POD, EC50 and RP of yam flours TF
TSP
PPO
POD
TF
1
TSP
-.095
1
PPO
-.861**
.507
1
POD
-.736**
.694*
.868**
1
EC50
-.821**
-.292
.473
.371
RP
-.035
.684*
.496
.323
EC50
RP
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Parameter
1
-.376
1
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* P ≤ 0.05, ** P ≤ 0.01. TF, Total flavones; TSP, Total soluble polyphenols; PPO, polyphenol oxidase activity;
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POD, peroxidase activity; EC50, DPPH scavenging activity; RP, Reducing power.
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Fig.1
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Fig.2
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Fig.3
ACCEPTED MANUSCRIPT Highlights: Yam with hot air-drying at 60ºC had higher allantoin content. Yam with hot air-drying at 40ºC and 80ºC had higher resistant starch.
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Blanching (100ºC for 1min) was effective to inhibiting enzymatic browning of yam. Flavonoid ingredients of yam may be mainly substrate of enzymatic browning
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reaction.
S0023-6438(17)30279-7
DOI:
10.1016/j.lwt.2017.04.058
Reference:
YFSTL 6196
To appear in:
LWT - Food Science and Technology
Received Date: 28 January 2017 Revised Date:
15 April 2017
Accepted Date: 17 April 2017
Please cite this article as: Chen, X., Lu, J., Li, X., Wang, Y., Miao, J., Mao, X., Zhao, C., Gao, W., Effect of blanching and drying temperatures on starch-related physicochemical properties, bioactive components and antioxidant activities of yam flours, LWT - Food Science and Technology (2017), doi: 10.1016/j.lwt.2017.04.058. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Effect of blanching and drying temperatures on starch-related physicochemical
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properties, bioactive components and antioxidant activities of yam flours Xuetao Chen a1, Jun Lu a1, Xia Li a∗, Ying Wang a, Jing Miao a, Xinhui Mao a,
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Chengcheng Zhao a, Wenyuan Gao a∗
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a
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Pharmaceutical Science and Technology, Tianjin University, Tianjin 300072, China
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1
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The author contributed equally to this article
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Tianjin Key Laboratory for Modern Drug Delivery and High-Efficiency, School of
∗
Corresponding author: Dr. Xia Li, Tel: +86-22-8740 1895. E-mail address: [email protected]
∗
Corresponding author: Prof. Dr. Wenyuan Gao, Tel/Fax: +86-22-8740 1895 E-mail address: [email protected] 1
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ABSTRACT: The effects of blanching (in boiling water for 1min) and different hot air drying
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temperatures (40ºC, 60ºC and 80ºC) on the polyphenol oxidase (PPO), peroxidase
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(POD) and antioxidant activities, main bioactive components, as well as the
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starch-related physicochemical properties of yam flours were studied. The results of
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PPO and POD activities, and total flavone and total soluble polyphenol contents
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showed that blanching was effective to inhibiting enzymatic browning of yams, and
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the substrate of enzymatic browning reaction may be mainly flavonoid ingredients.
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The sample of H-40 had higher allantoin and total soluble polyphenol content,
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stronger DPPH scavenging activity and reducing power. From the results of scanning
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electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared
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(FT-IR), the blanching yams was found contain partly gelatinized starch granules, and
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had lower crystallinity. The H-40 and H-80 samples had higher RS contents and lower
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GI values. Furthermore, the protein and soluble amylose contents, solubility and
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swelling power at 90ºC of the blanching yams were lower than those of the yams
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without blanching. We can effectively apply these flours in various products based on
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their characteristics.
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Keywords: Yam flour; Blanching；Drying temperature; Starch; Antioxidant capacity
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1. Introduction Yams, the tuber of Dioscorea opposita Thunb., have been considered as a
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superior Chinese herb to improve functions of stomach and spleen (SPC, 2015), as
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well as the fourth major root crop in the world after cassava, potatoes and sweet
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potatoes (Akinoso and Olatoye, 2013). The major active components in yams are
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allantoin, phenolic compounds, and others (Niu et al., 2010; Muzac-Tucker et al.,
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1993). Nonetheless, starch is the predominant fraction of yams, making up
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approximately 75-84% of the total biomass.
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Fresh yams are difficult to store and are susceptible to deterioration during
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storage. Dried yam slices and flours are the main products in the market, which can be
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easily stored in the long term and conveniently consumed in these forms. Our
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previous studies (Chen et al., 2017) have found that hot air drying (HAD) at 60ºC
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would be a better method for yam drying. Several studies have reported the effect of
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different drying temperatures on the physio-chemical and starch-related properties.
41
(Correia and Beirão-da-Costa, 2012; Attanasio et al., 2004; Falade et al., 2007).
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Therefore, study on the effects of different drying temperatures on the properties of
43
yam flours is very necessary. In addition to this, fresh-cut processing, such as peeling
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and cutting, may accelerates physiological deterioration, which leads to yam
45
browning. Browning, decline in the nutritional quality and overall visual quality of
46
yams, severely decreases its market potential. This browning known as enzymatic
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browning reactions (Bhandari and Kawabata, 2004) is attributed to the oxidation of
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phenolic compounds by polyphenol oxidase (PPO) and peroxidase (POD). The
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ACCEPTED MANUSCRIPT phenolic compounds were oxidized to quinones, in turn these were polymerized to
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form brown pigments (Queiroz et al., 2008). Barrett et al. (1991) reported the
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condition of mechanical injury may result in changes in cell membrane permeability
52
and release of either stored substrates from the vacuole or bound enzymes from
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organelles, which may be involved in enzymatic browning.
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Some measures have been used to inhibit enzymatic browning of yam during
55
processing. These approaches include sulfur fumigation (Jiang et al., 2013), soaking
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in chemicals (Krishnan et al., 2010), and electrolyzed water (Jia et al., 2015).
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However, these measures more or less had chemical residues, to which consumers
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don't want. Birch et al. reported that the most of the enzyme kept in hot water of
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100ºC for 1 min would be inactivation (Birch et al., 2012; Desrosier et al., 1977).
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Blanching is an effective and commonly used method, which has relatively low costs.
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In this study, according to the previous research (Chen et al., 2017) and practical
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production, we chose 60ºC, 40ºC (lower than 60ºC) and 80ºC (higher than 60ºC) for
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yams drying, and determined the effects of blanching and different drying
64
temperatures on starch-related properties, and bioactive components' contents, as well
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as antioxidant capacity. Finally, aiming toward an effective utilization of these flours
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in various food products.
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2. Materials and methods
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2.1. The preparation of dried yam flours
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Fresh Chinese yam (Dioscorea opposita) was collected from Wen town, Jiaozuo
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city, Henan Province in China. The yam tubers were washed, peeled, then cut into 4
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slices were divided into 3 subgroups, and they were dried in hot air drying oven
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(DL-101-1S, Tianjin Central Lab Electric Furnace Co., Ltd., China) with air speed
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0.15 m/s, at 40ºC for 10h (H-40), 60ºC for 6h (H-60), and 80ºC for 3 h (H-80),
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respectively. Another group of slices were blanched in a boiling water bath (about
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100ºC) for 1 min, the blanched yam slices were divided into three subgroups, and
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dried in hot air drying oven with air speed 0.15 m/s, at 40ºC for 10h (BH-40), 60ºC
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for 6h (BH-60), and 80ºC for 3 h (BH-80), respectively.
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The dried yam samples were ground in a blender (WND-200, Lanxi Weinengda
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Electric Co., Ltd. Zhejiang, China), and sieved through a screen (75±4.1 µm) to obtain
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yam flours.
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2.2. Moisture, protein, and total starch content determination
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The moisture content of the yam flour was analyzed according to SPC (2015).
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The protein contents of the yam flours were determined according to Bradford’s dye
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binding method, using bovine serum albumin (BSA) as standard (Bradford, 1976).
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The total starch content of the yam flour was determined using enzymatic hydrolysis,
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described by Jiang et al. (2010).
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2.3. Apparent amylose content and soluble amylose content
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The apparent amylose contents and the soluble amylose contents of yam flour
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was estimated by using the method of Chen et al. (2016).
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2.4. Water-binding capacity (WBC)
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Water-binding capacity (WBC) of the yam flour was determined according to the 5
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previous reported method (Chen et al., 2017).
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2.5. Swelling power (SP) and solubility (SOL) Solubility and the swelling power were measured according to a method
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described by Chen et al. (2017).
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2.6. Scanning electron microscopy (SEM)
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The morphological features of the yam flours were observed with an
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environmental scanning electron microscope (SEM, Shimadzu SS-550). The dried
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samples were mounted on a metal stub, coated with gold powder to make the sample
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conductive, and images were then taken with an accelerating voltage of 1.9 kV.
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2.7. X-ray diffraction (XRD)
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X-ray diffraction patterns of the yam flours were analyzed according to the previous reported method (Chen et al., 2017).
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2.8. Fourier transform infrared spectroscopy (FT-IR)
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Fourier transform infrared spectroscopy observed according to the previous reported method (Chen et al., 2017).
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2.9. In vitro digestibility
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The in vitro digestibilities of the yam flours were determined according to the
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procedure of Chen et al. (2017).
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2.10. Polyphenol oxidase (PPO) and peroxidase (POD) activities
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The PPO and POD activities were determined by the method described by Jia et
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al. (2015) with some modifications. Extraction solution was 2 g polyvinyl
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polypyrolidone (PVPP) mixed with 100mL sodium phosphate buffer (0.2 mol/L, pH 6
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total of 2 mL of extraction solution was added to the tube, stirred up the extraction
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solution for 1 min. The mixture was centrifuged at 12000x g for 5 min at 4 °C. This
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extraction and collection was repeated three times. The supernatant was collected for
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determinations of the PPO and POD activity.
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The substrate was 1.5 mL of 20 mg/mL catechol. Other reaction mixtures
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included 1.5 mL of 50 mmol/L phosphate buffer (pH 7.0), and 0.2 mL of the enzyme
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solution. For the blank sample, 0.2 mL of phosphate buffer was used instead of 0.2
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mL enzyme solution. The PPO activity was determined as the amount of the enzyme
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catalyzing a linear increase of 0.001 absorbance per minute per gram yam flour at 410
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nm.
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The substrate was 25 mmol/L guaiacol and 25 mmol/L hydrogen peroxide
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dissolved in 0.05 mol/L sodium phosphate buffer (pH 7.0). The reactant contained 2.8
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mL substrate and 0.2 mL enzyme solution. For the blank sample, 0.2 mL of phosphate
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buffer was used instead of 0.2 mL enzyme solution. The POD activity unit (U) was
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defined as a 0.001 linear increase in absorbance per minute per gram fresh weight at
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470 nm.
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2.11. Preparation of methanol sample extracts for determination of soluble phenolic,
133
flavonoids, and allantoin contents, as well as antioxidant activity assays
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Yam flours (4 g) were placed into test tubes. A total of 15 mL of 80 mL/100mL
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methanol was added to each tube, and the tubes were sonicated for 30 min at room
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temperature. After centrifugation at 3000x g for 5 min, the supernatant was collected. 7
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extract was concentrated by vacuum rotary evaporation at 50°C, dissolved in 80
139
mL/100mL methanol to yield 10 mL of total solution, which was used for
140
determination soluble phenolic, flavonoids, and allantoin contents, as well as reducing
141
power. The methanolic yam extract (400 mg/mL) was diluted to the following
142
concentrations for the DPPH radical scavenging test: 10, 20, 30, 40, 50, 60 and 70
143
mg/mL.
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2.12. Determination of total soluble polyphenol and total flavonoid content
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Determinations of the total soluble polyphenol and total flavonoid contents of
146
samples were performed using the methods previously reported (Chen et al., 2017).
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2.13. Determination of allantoin content
Determination of allantoin content according the method described in the
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previously report (Chen et al., 2017).
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2.14. Determination of antioxidant activity Antioxidant activity of yam flours evaluated by DPPH radical scavenging and
152
reducing power assay. The methods of DPPH radical scavenging and reducing power
153
test were previously report (Chen et al., 2017).
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2.15. Statistical analysis
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All determinations were performed in triplicate, and the data were expressed as
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the mean values ± SD. Analysis of variance was performed to calculate significant
157
differences by Student-Newman-Keuls (SNK) and least -significant difference (LSD)
158
post hoc test for univariate comparison (P ≤ 0.05). The data were statistically 8
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analyzed using the IBM SPSS Statistics 20 (SPSS Inc. Chicago, IL, USA).
160
3. Results and discussion
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3.1. Total starch, amylose, protein, and WBC The moisture content of yam flours ranged from 5.85 g/100g to 12.66 g/100g,
163
and the blanching samples showed higher moisture content than samples without
164
blanching at same drying temperature (Table 1). This phenomenon may be due to the
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fact that the blanching led to starch gelatinization, and during the subsequent drying
166
process a resistant film layer was formed on the surface of the samples, which
167
reduced water transfer (Xiao et al., 2012).
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The total starch content was from 67.08 g/100g to 77.52 g/100g, and the
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blanching samples presented lower total starch content values than samples dried at
170
temperatures of 40ºC and 60ºC (Table 1). The results showed that the total starch
171
content was decreased with drying temperature increasing. These phenomena may be
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explained by the result that the thermal treatments caused the formation of modified
173
starch, which is not detectable by the enzymatic test (Voragen, 1998).
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Concerning protein content in both samples (Table 1), the blanching samples
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present lower protein content values, and the protein content decreased with drying
176
temperature increasing. These differences among protein content could be due to
177
denaturation or changes in solubility during blanching and heating, which may have
178
caused the proteins to leach out into the water (Danso-Boateng, 2013).
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The apparent amylose contents of blanching samples (10.31 g/100g - 12.66
180
g/100g) were higher than the samples without blanching dried at the same temperature 9
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182
g/100g - 5.57 g/100g) was lower than the without blanching samples (7.17 g/100g -
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7.50 g/100g). The H-60 sample had higher soluble amylose content among all
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samples, and the soluble amylose content of BH-60 sample was higher among the
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blanching samples. The reason of these phenomena possibly was the increase
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combined action of enzymes on starch during the yam drying process (Correia et al.,
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2009). These enzymes mainly include α-amylase, β-amylase, glucoamylase, and
188
pullulanase, which are optimum active at temperature between 55ºC and 60ºC
189
(Correia and Beirão-da-Costa, 2012). The insoluble amylose content ranged from 1.27
190
g/100g to 9.66 g/100g. It has been reported that the insoluble amylose was related to
191
the long chain B of the amylopectin molecule (Takeda et al., 1987).The insoluble
192
amylose contents of blanching samples were higher than those without blanching
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samples. This phenomenon may be attributed to the thermal degradation of the
194
amylopectin (Dharmaraj and Malleshi, 2011), and the dissociation and reaggregation
195
of
196
amylose-amylose, amylose-amylopectin chains and amylose-lipids during blanching
197
process (Raja and Sindhu, 2000).
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The WBC of all samples ranged from 188.02 g/100g to 257.15 g/100g, and the
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blanching samples dried at temperatures of 40ºC and 60ºC present higher WBC values
200
than others, while the BH-80 sample had lower WBC value. The WBC value of
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samples without blanching increased with the temperature increasing. These
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phenomena may be due to the fact that higher temperature produced in blanching and 10
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2014). Rayas-Duarte et al. (1998) reported that the degree of starch gelatinization and
205
fragmentation may be considered among the main factors affecting the WBC.
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3.2. Swelling power and solubility
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The swelling powers and solubilities of all the yam flours at temperatures in the
208
range between 50ºC to 90ºC are presented in Table 2. The swelling power and
209
solubility of each sample showed a continuous increase with increasing drying
210
temperature. The extent of this increase was more pronounced at temperatures beyond
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70ºC. The swelling powers of blanching yam flours were lower than those samples
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without blanching at 80ºC and 90ºC. The solubility of each blanching sample was
213
lower than the sample without blanching dried at the same temperature. The increased
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insoluble amylose contents in blanching samples (Table 1), which may facilitate
215
additional interaction between amylose-amylose and/or amylose-amylopectin, as well
216
as formed amylose-lipid complexes, may be responsible for decreasing of the swelling
217
powers and solubilities of blanching samples (Gunaratne and Hoover, 2002). Tester
218
and Morrison (1990) comparatively studied on the non-waxy and waxy maize starch,
219
and reported that swelling is primarily a property of amylopectin, while amylose acts
220
as an inhibitor of swelling. Cooke and Gidley (1992) have suggested that the forces
221
holding the granule together are mainly at the double helical level and that the starch
222
‘crystallinity’ functions as a means of achieving dense packing rather than as primary
223
provider of structure. These imply that the lower swelling powers in blanching
224
samples could also be due to the decreased of granular stabilities, resulting from the
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thermal degradation of the amylopectin, which led to the unraveling of double helices.
226
3.3. Scanning electron microscopy (SEM) The SEM of all the yam flours is shown in Fig. 1. The starch granules of samples
228
without blanching presented oval and spherical shaped with size ranging from 8 to
229
35µm. There was no significant difference of morphology among samples dried with
230
different temperature. However, major differences were found in chestnut flours dried
231
at different temperatures, the gelatinization phenomena is quicker in starch granules
232
from chestnut flours drying at high temperature (Correia et al., 2012). The granules of
233
blanching samples presented different shapes and sizes, which partly have gelatinized.
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The ungelatinized granules showed the similar shapes and sizes to granules of
235
samples without blanching. Some gelatinized granules become large masses, which
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showed characteristic block and irregular structure, and had a cranny and rough
237
surface. The results may be due to the fact that partial gelatinization and subsequent
238
retrogradation of starch which appeared to be bonded together by binders like water
239
and gelatinized starch (Kuttigounder et al., 2011; Dhanalakshmi & Bhattacharya,
240
2014).
241
possibly due to the decreased moisture (binder of reassociated starch). The most
242
gelatinized granules of BH-40 sample become large masses (100-140 µm), which
243
showed characteristic block and irregular structure, and had a cranny and rough
244
surface. There were large masses and small fragments in the BH-60 sample. The most
245
gelatinized granules of BH-80 sample were small fragments, which had large range of
246
size (30-100 µm), irregular structure, and a cranny and rough surface.
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3.4. X-ray diffraction (XRD) The samples dried by different temperatures, both of blanching and without
249
blanching, shown A - type XRD patterns with reflection intensities at 2θ values of
250
15.0º, 17.0º, 17.8º, 19.5º and 23º (Fig. 2). The relative crystallinities of blanching
251
samples (9.35%-14.28%) were lower than those the samples without blanching
252
(16.26%-23.88%), and the relative crystallinity decreased with increasing drying
253
temperature (Table 3). The differences in relative crystallinity among different yam
254
flours probably represent differences in the orientational order parameter of the
255
amylopectin double helices and average chain length of amylopectin, as well as mole
256
percentage of the short chain fraction of amylopectin (Gunaratne and Hoover, 2002;
257
Waigh et al., 2000). From the SEM of blanching samples (Fig.1), we found that the
258
partly starch granules gelatinized. Waigh et al. (2000) reported that there were two
259
transformations (crystalline smectic to isotropic/nematic transition at lower
260
temperatures and helix-coil transition at higher temperatures) in starch during
261
gelatinization, which led to the lower crystallinities.
262
3.5. Fourier transform infrared (FT - IR)
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The FT - IR spectra of starches have been shown to be sensitive to changes in
264
structure on a molecular level (short-range order), such as changes in chain
265
conformation and double helical order (van Soest et al., 1995). The absorption region
266
from 800 to 1200 cm-1 of deconvoluted FT - IR spectra of the studied yam flours are
267
presented in Fig. 3. This region of the IR spectra is characterized by these main modes
268
with maximum absorbance at 995, 1022, 1035 and 1047 cm-1 (van Soest et al., 1995). 13
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270
short-range order of starch, the absorption band at 1022 cm-1 is associated with the
271
amorphous structures of starch, and the band at 995 cm-1 is ascribed to a single-helix
272
crystalline structure environment (Jiang et al., 2014; van Soest et al., 1995). The ratios
273
of peak intensities at 1047/1022 (R1047/1022) and 995/1022 (R995/1022) are used to
274
compare the degrees of crystallinity and molecular order of the starches. The ratio of
275
peak intensities at 1047/1035 (R1047/1035) expresses the amount of ordered starch,
276
which is very sensitive to water content (Mutungi et al., 2011; van Soest et al., 1995).
277
The values of R1047/1022, R1047/1035 and R995/1022 were calculated (Table 3). The R1047/1022
278
values ranged from 0.9117 for BH-80 sample to 0.9759 for BH-40 sample, and the
279
R995/1022 values ranged from 0.9510 for the BH-40 sample to 1.1017 for the H-40
280
sample, which had different trend with crystallinity. The similar results reported in the
281
literature of Lan et al. (2016), and the results may be due to the fact that crystallinity
282
from XRD is a measure of long-range order, which would not necessarily be present
283
when short-range order exists. The R995/1022 values ranged from 0.9510 for the BH-40
284
sample to 1.1017 for the H-40 sample, and the R1047/1035 values ranged from 0.9807
285
for the BH-80 sample to 1.0063 for the H-40 sample in line with the same observed
286
trend in crystallinity.
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3.6. In vitro digestibility
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The in vitro digestibilities of starches from the yam flours were evaluated by
289
determining the RDS, SDS and RS contents (Table 3). The RS contents of blanching
290
samples (36.20-46.98%) were lower than those samples without blanching 14
ACCEPTED MANUSCRIPT (55.44-62.63%). The reasons for this was that blanching led to greater degree of
292
starch gelatinization, irregular shaped starch granules, cranny and rough surface,
293
lower protein content, lower degree of crystallinity, and thermal degradation of the
294
amylopectin. These factors may have made it easier for enzyme to attack the chains,
295
which have been reported in the literature (Dhital et al., 2010; Chung and Liu, 2012).
296
The samples of H-80 (50.18%) and H-40 (54.72%) had a low GI (GI ≤ 55), H-60
297
(64.41%) and BH-80 (66.25%) had an intermediate GI (GI, 56-69), BH-40 (69.81%)
298
and BH-60 (81.76%) had a high GI (GI ≥ 70) (Moraes et al., 2015).
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3.7. Polyphenol oxidase (PPO) and Peroxidase (POD) activities
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The effect of blanching and different temperatures on PPO and POD activities of
301
yam flours is shown in Table 4. The PPO activities of blanching samples (0.004-0.007
302
AU/g•min) were significant lower than those without blanching samples (0.015-0.028
303
AU/g•min). The POD activities of yam flours had the same trend with PPO activities.
304
The POD activities of blanching samples was lower (0.0003-0.0007 AU/g•min),
305
while those of the samples without blanching was higher (0.0011-0.0020 AU/g•min).
306
The result is consistent with Landymore’s (2001) report, which find that the enzymes
307
would instantaneously lose activity at moist heat temperatures near the boiling point
308
of water. The PPO and POD activities decreased with increasing temperature. The
309
phenomenon may be due to the fact that PPO and POD is sensitive to thermal, and
310
had maximum activity at 30ºC and 35ºC, respectively (Zhang and Shao, 2015).
311
Landymore (2001) reported that an increase of 10ºC, the inactivation rate will
312
increase sixty-four-fold.
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3.8. Bioactive components in the yam flours The observed allantoin, total flavone, and total soluble phenolic contents are
315
shown in Table 4. The allantoin content of the H-60 (0.155g/100g) was the highest,
316
followed by H-40 (0.149 g/100g), BH-60 (0.095 g/100g), BH-80 (0.078 g/100g), H-80
317
(0.075 g/100g), and BH-40 (0.066 g/100g). The allantoin was synthesized in roots
318
mainly via purine degradation process, which involved in some enzymes (mainly,
319
xanthine oxidase, uricase and allantoinase) (Thomas and Schrader, 1981). Therefore,
320
the lower allantoin content in those samples (BH-60, BH-80, H-80, and BH-40) may
321
be due to the activity of enzyme, which was inhibited during blanching and high
322
temperature heating processes.
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Total soluble phenolic contents ranged from 0.57 mg CE/g for BH-80 sample to
324
1.05 mg CE/g for H-40 sample, and total soluble phenolic content of H-40 sample
325
much higher than others. The total soluble phenolic contents decreased with
326
temperatures increasing, and total soluble phenolic contents of BH-40 and BH-80
327
samples significant decreased compared with those of H-40 and H-80 samples,
328
respectively. Those phenomena may be due to thermal degradation (autoxidation or
329
breakdown) during blanching and high temperature heating processes, and diffusion
330
or/and leaching into the water during blanching (Jaiswal et al., 2012; Gonçalves et al.,
331
2010). The total flavones contents of blanching samples (0.50-0.60 mg RE/g) were
332
higher than those samples without blanching (0.35-0.49 mg RE/g). The significant
333
negative correlation was found between total flavones contents and PPO activities (r =
334
-0.861, P ≤ 0.01, Table 5), POD activities (r = -0.736, P ≤ 0.01, Table 5). This
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phenomenon suggested that the substrate of enzymatic browning reaction was mainly
336
flavonoid ingredients.
337
3.9. Antioxidant capacities of the flours The antioxidant capacities of yam flours were evaluated by a DPPH radical assay
339
and a reducing power assay (Table 4). The H-40 sample showed strong (EC50 value
340
was 87.00 mg/mL) DPPH radical scavenging activity, followed by BH-60 (EC50 value
341
was 106.45 mg/mL), BH-40 (EC50 value was 111.10 mg/mL), H-60 (EC50 value was
342
142.50 mg/mL), BH-80 (EC50 value was 158.15 mg/mL), and H-80 (EC50 value was
343
189.15 mg/mL). The EC50 value of the DPPH radical scavenging activity was
344
negatively correlated with total flavonoid content (r = -0.821, P ≤ 0.01, Table 5). The
345
result suggested that total flavonoid content is largely responsible for the DPPH
346
radical scavenging activity.
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The reducing powers of the H-40 (147.76 µmol AC/g dw) was the highest,
348
followed by BH-80 (128.40 µmol AC/g dw) and H-60 (126.50 µmol AC/g dw),
349
BH-60 (112.96 µmol AC/g dw), BH-40 (103.32 µmol AC/g dw), and H-80 (93.39
350
µmol AC/g dw). Reducing power was statistically determined to be positively
351
correlated to total soluble phenolic content (r = 0.684, P ≤ 0.05, Table 5). The result
352
suggested that total soluble phenolic content is largely responsible for the reducing
353
power.
354
4. Conclusions
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The blanching pre-treatment at boiling water (about 100ºC) for 1min, was
356
effective to inhibiting enzymatic browning of yams, and the substrate of enzymatic 17
ACCEPTED MANUSCRIPT browning reaction was mainly flavonoid ingredients. The sample of H-40, had higher
358
allantoin and total soluble polyphenol content, stronger DPPH scavenging activity and
359
reducing power, which is an important source of functional foods that are increasingly
360
popular today. From the perspective of the starch-related properties, the partly starch
361
granules of blanching samples was gelatinization, and the crystallinity was lower. The
362
H-40 and H-80 samples, which had higher RS contents and lower GI values, are ideal
363
for preparing hypoglycemic and lipid-lowering functional foods. What’s more, the
364
protein and soluble amylose contents, solubility and swelling power at 90ºC of the
365
blanching yams were lower than those of the yams without blanching. Based on their
366
characteristics, these flours can be effectively applied in various products. In order to
367
fully understand the effect of blanching and hot air drying, further characterization of
368
the phenolic compounds as future work needs to be done.
369
Conflict of interest
370
The authors have declared no conflict of interest.
371
Acknowledgments
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This work was financially supported by Special Scientific Research of Chinese
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Medicine Industry (201307008) from the State Administration of Traditional Chinese
374
Medicine, Science and Technology Program of China (NO. 2014FY111100).
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ACCEPTED MANUSCRIPT References
376
Akinoso, R., & Olatoye, K. K. (2013). Energy utilization and conservation in
377
instant-pounded yam flour production. International Food Research Journal, 20,
378
575-579.
RI PT
375
Attanasio, G., Cinquanta, L., Albanese, D., & Di Matteo, M. (2004). Effects of drying
380
temperatures on physico-chemical properties of dried and rehydrated chestnuts
381
(Castanea sativa). Food Chemistry, 88, 583-590.
SC
379
Barrett, D. M., Lee, C. Y., & Liu, F. W. (1991). Changes in the activity and subcellular
383
distribution of ppo in ‘delicious’ apples during controlled atmosphere storage.
384
Journal of Food Biochemistry, 15, 185-199.
386
Birch, G. G., Blakebrough, N., & Parker, K. J. (2012). Enzymes and food processing. Springer Science & Business Media.
TE D
385
M AN U
382
Bhandari, M. R., & Kawabata, J. (2004). Organic acid, phenolic content and
388
antioxidant activity of wild yam (Dioscorea spp.) tubers of Nepal. Food
389
Chemistry, 88, 163-168.
391 392
Bradford, M. M., 1976. A rapid and sensitive method for the quantitation of
AC C
390
EP
387
microgram quantities of protein utilizing the principle of protein-dye binding. Analytical Biochemistry, 72, 248-254.
393
Chen, X., Li, X., Mao, X., Huang, H., Miao, J., & Gao, W. (2016). Study on the
394
effects of different drying methods on physicochemical properties, structure, and
395
in vitro digestibility of Fritillaria thunbergii Miq. (Zhebeimu) flours. Food and
396
Bioproducts Processing, 98, 266-274. 19
ACCEPTED MANUSCRIPT Chen, X., Li, X., Mao, X., Huang, H., Wang, T., Qu, Z., ... & Gao, W. (2017). Effects
398
of drying processes on starch-related physicochemical properties, bioactive
399
components and antioxidant properties of yam flours. Food Chemistry, 224,
400
224-232.
RI PT
397
Chiu, C. S., Deng, J. S., Chang, H. Y., Chen, Y. C., Lee, M. M., Hou, W. C., Lee, C. Y.,
402
Huange, S. S., & Huang, G. J. (2013). Antioxidant and anti-inflammatory
403
properties of taiwanese yam (Dioscorea japonica Thunb. Var. pseudojaponica
404
(Hayata) Yamam.) and its reference compounds. Food Chemistry, 141,
405
1087-1096.
M AN U
SC
401
Chung, H. J., & Liu, Q. (2012). Physicochemical properties and in vitro digestibility
407
of flour and starch from pea (Pisum sativum L.) cultivars. International Journal
408
of Biological Macromolecules, 50, 131-137.
TE D
406
Cooke, D., & Gidley, M. J. (1992). Loss of crystalline and molecular order during
410
starch gelatinisation: origin of the enthalpic transition. Carbohydrate Research,
411
227, 103-112.
413 414
Correia, P., Leitão, A., & Beirão-da-Costa, M. L. (2009). The effect of drying
AC C
412
EP
409
temperatures on morphological and chemical properties of dried chestnuts flours. Journal of Food Engineering, 90(3), 325-332.
415
Correia, P., & Beirão-da-Costa, M. L. (2012). Effect of drying temperatures on
416
starch-related functional and thermal properties of chestnut flours. Food and
417
Bioproducts Processing, 90, 284-294.
418
Danso-Boateng, E. (2013). Effect of drying methods on nutrient quality of Basil 20
ACCEPTED MANUSCRIPT 419
(Ocimum viride) leaves cultivated in Ghana. International Food Research
420
Journal, 20, 1569-1573.
422 423 424
Desrosier, N. W., & Desrosier, J. N. (1977). The technology of food preservation (No. Ed. 4). AVI Publishing Company, Inc..
RI PT
421
Dhital, S., Shrestha, A. K., & Gidley, M. J. (2010). Effect of cryo-milling on starches: Functionality and digestibility. Food Hydrocolloids, 24, 152-163.
Dharmaraj, U., & Malleshi, N. G. (2011). Changes in carbohydrates, proteins and
426
lipids of finger millet after hydrothermal processing. LWT-Food Science and
427
Technology,, 44, 1636-1642.
M AN U
SC
425
Dhanalakshmi, K., & Bhattacharya, S. (2014). Agglomeration of turmeric powder and
429
its effect on physico-chemical and microstructural characteristics. Journal of
430
Food Engineering, 120, 124-134.
TE D
428
Falade, K. O., Olurin, T. O., Ike, E. A., & Aworh, O. C. (2007). Effect of pretreatment
432
and temperature on air-drying of Dioscorea alata and Dioscorea rotundata slices.
433
Journal of Food Engineering, 80, 1002-1010.
435 436
Gonçalves, E. M., Pinheiro, J., Abreu, M., Brandão, T. R. S., & Silva, C. L. (2010).
AC C
434
EP
431
Carrot (Daucus carota L.) peroxidase inactivation, phenolic content and physical changes kinetics due to blanching. Journal of Food Engineering, 97, 574-581.
437
Gunaratne, A., & Hoover, R. (2002). Effect of heat-moisture treatment on the
438
structure and physicochemical properties of tuber and root starches.
439
Carbohydrate Polymers, 49, 425-437.
440
Jaiswal, A. K., Gupta, S., & Abu-Ghannam, N. (2012). Kinetic evaluation of colour, 21
ACCEPTED MANUSCRIPT 441
texture, polyphenols and antioxidant capacity of Irish York cabbage after
442
blanching treatment. Food Chemistry, 131, 63-72. Jia, G. L., Shi, J. Y., Song, Z. H., & Li, F. D. (2015). Prevention of enzymatic
444
browning of Chinese yam (Dioscorea spp.) using electrolyzed oxidizing water.
445
Journal of Food Science, 80, C718-C728.
RI PT
443
Jiang, H., Jane, J. L., Acevedo, D., Green, A., Shinn, G., Schrenker,D., Srichuwong,
447
S., Campbell, M., Wu, Y., 2010. Variations in starch physicochemical properties
448
from a generation-means analysis study using amylomaize V and VII parents.
449
Journal of Agricultural and Food Chemistry, 58, 5633-5639.
M AN U
SC
446
Jiang, Q., Gao, W., Shi, Y., Li, X., Wang, H., Huang, L., & Xiao, P. (2013).
451
Physicochemical properties and in vitro digestion of starches from different
452
Dioscorea plants. Food Hydrocolloids, 32, 432-439.
TE D
450
Jiang, X., Huang, L. F., Zheng, S. H., & Chen, S. L. (2013). Sulfur fumigation, a
454
better or worse choice in preservation of traditional Chinese medicine?
455
Phytomedicine, 20, 97-105.
457 458 459
Jiang, Q., Gao, W., Li, X., Man, S., Shi, Y., Yang, Y., ... & Liu, C. (2014).
AC C
456
EP
453
Comparative susceptibilities to alkali-treatment of A-, B-and C-type starches of Dioscorea zingiberensis, Dioscorea persimilis and Dioscorea opposita. Food Hydrocolloids, 39, 286-294.
460
Krishnan, J. G., Padmaja, G., Moorthy, S. N., Suja, G., & Sajeev, M. S. (2010). Effect
461
of pre-soaking treatments on the nutritional profile and browning index of sweet
462
potato and yam flours. Innovative Food Science & Emerging Technologies, 11, 22
ACCEPTED MANUSCRIPT 463
387-393. Kuttigounder, D., Lingamallu, J. R., & Bhattacharya, S. (2011). Turmeric powder and
465
starch: selected physical, physicochemical, and microstructural properties.
466
Journal of Food Science, 76, C1284-C1291.
RI PT
464
Landymore, C. L. (2001). Evaluation of protein utilisation of vacuum microwave, air,
468
and freeze-dried Euphausia pacifica in a rat model (Doctoral dissertation,
469
University of British Columbia).
SC
467
Lan, X., Xie, S., Wu, J., Xie, F., Liu, X., & Wang, Z. (2016). Thermal and enzymatic
471
degradation induced ultrastructure changes in canna starch: Further insights into
472
short-range and long-range structural orders. Food Hydrocolloids, 58, 335-342.
M AN U
470
Liyana-Pathirana, C. M., & Shahidi, F. (2007). Antioxidant and free radical
474
scavenging activities of whole wheat and milling fractions. Food Chemistry, 101,
475
1151-1157.
TE D
473
Moraes, É. A., da Silva Marineli, R., Lenquiste, S. A., Steel, C. J., de Menezes, C. B.,
477
Queiroz, V. A. V., & Júnior, M. R. M. (2015). Sorghum flour fractions:
478
Correlations among polysaccharides, phenolic compounds, antioxidant activity
AC C
479
EP
476
and glycemic index. Food Chemistry, 180, 116-123.
480
Muzac-Tucker, I., Asemota, H. N., & Ahmad, M. H. (1993). Biochemical composition
481
and storage of Jamaican yams (Dioscorea sp). Journal of the Science of Food
482
and Agriculture, 62, 219-224.
483
Mutungi, C., Onyango, C., Doert, T., Paasch, S., Thiele, S., Machill, S., Jaros, D., &
484
Rohm, H. (2011). Long- and short-range structural changes of recrystallised 23
ACCEPTED MANUSCRIPT 485
cassava starch subjected to in vitro digestion. Food Hydrocolloids, 25, 477-485. Niu, C. S., Chen, W., Wu, H. T., Cheng, K. C., Wen, Y. J., Lin, K. C., & Cheng, J. T.
487
(2010). Decrease of plasma glucose by allantoin, an active principle of yam
488
(Dioscorea spp.), in streptozotocin-induced diabetic rats. Journal of Agricultural
489
and Food Chemistry, 58, 12031-12035.
RI PT
486
Queiroz, C., Mendes Lopes, M. L., Fialho, E., & Valente-Mesquita, V. L. (2008).
491
Polyphenol oxidase: characteristics and mechanisms of browning control. Food
492
Reviews International, 24, 361-375.
494
M AN U
493
SC
490
Raja, M. K., & Sindhu, P. (2000). Properties of Steam-Treated Arrowroot (Maranta arundinacea) Starch. Starch‐Stärke, 52, 471-476.
Rayas-Duarte, P., Majewska, K., & Doetkott, C. (1998). Effect of extrusion process
496
parameters on the quality of buckwheat flour mixes 1. Cereal Chemistry, 75,
497
338-345.
500 501 502 503 504 505 506
China Medical Science and Technology Press, Beijing.
EP
499
State Pharmacopoeia Committee, 2015. Pharmacopeia of People’s Republic of China.
Tacer-Caba, Z., Nilufer-Erdil, D., Boyacioglu, M. H., & Ng, P. K. (2014). Evaluating
AC C
498
TE D
495
the effects of amylose and Concord grape extract powder substitution on physicochemical properties of wheat flour extrudates produced at different temperatures. Food Chemistry, 157, 476-484.
Takeda, Y., Hizukuri, S., & Juliano, B. O. (1987). Structures of rice amylopectins with low and high affinities for iodine. Carbohydrate Research, 168, 79-88. Tester, R. F., & Morrison, W. R. (1990). Swelling and gelatinization of cereal starches. 24
ACCEPTED MANUSCRIPT 507 508 509
I. Effects of amylopectin, amylose, and lipids. Cereal Chemistry, 67, 551-557. Thomas, R. J., & Schrader, L. E. (1981). Ureide metabolism in higher plants. Phytochemistry, 20, 361-371. van Soest, J. J., Tournois, H., de Wit, D., & Vliegenthart, J. F. (1995). Short-range
511
structure in (partially) crystalline potato starch determined with attenuated total
512
reflectance Fourier-transform IR spectroscopy. Carbohydrate Research, 279,
513
201-214.
515
SC
Voragen, A. G. (1998). Technological aspects of functional food-related carbohydrates.
M AN U
514
RI PT
510
Trends in Food Science & Technology, 9, 328-335.
Waigh, T. A., Gidley, M. J., Komanshek, B. U., & Donald, A. M. (2000). The phase
517
transformations in starch during gelatinisation: a liquid crystalline approach.
518
Carbohydrate Research, 328, 165-176.
TE D
516
Wang, S. J., Yu, J. L., Gao, W, Y., Pang, J. P., Liu, H, Y., & Yu, J, G. (2007). Granule
520
structural changes in native Chinese Yam (Dioscorea opposita Thunb var. Anguo)
521
starch during acid hydrolysis. Carbohydrate Polymers, 69, 286-292.
523 524
Xia, X., Cao, J., Zheng, Y., Wang, Q., & Xiao, J. (2014). Flavonoid concentrations
AC C
522
EP
519
and bioactivity of flavonoid extracts from 19 species of ferns from China. Industrial Crops and Products, 58, 91-98.
525
Xiao, H. W., Yao, X. D., Lin, H., Yang, W. X., Meng, J. S., & Gao, Z. J. (2012). Effect
526
of SSB (superheated steam blanching) time and drying temperature on hot air
527
impingement drying kinetics and quality attributes of yam slices. Journal of
528
Food Process Engineering, 35, 370-390. 25
ACCEPTED MANUSCRIPT
TE D
M AN U
SC
RI PT
and the role in browning of loquat fruit. Journal of Food Science, 33, 109-117.
EP
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Zhang, X., & Shao, X. (2015). Characterisation of polyphenol oxidase and peroxidase
AC C
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Fig. 1.
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Scannjng electron microphs (SEM) of yam flours. H-40, Hot air drying at 40ºC;
534
BH-40, Hot air drying at 40ºC after blanching; H-60, Hot air drying at 60ºC; BH-60,
535
Hot air drying at 60ºC after blanching; H-80, Hot air drying at 80ºC; BH-80, Hot air
536
drying at 80ºC after blanching.
537
Fig. 2.
538
X-ray diffraction (XRD) of yam flours. a, Hot air drying at 40ºC; b, Hot air drying at
539
40ºC after blanching; c, Hot air drying at 60ºC; d, Hot air drying at 60ºC after
540
blanching; e, Hot air drying at 80ºC; f, Hot air drying at 80ºC after blanching.
541
Fig. 3.
542
Deconvoluted FT - IR spectra of yam flours. a, Hot air drying at 40ºC; b, Hot air
543
drying at 40ºC after blanching; c, Hot air drying at 60ºC; d, Hot air drying at 60ºC
544
after blanching; e, Hot air drying at 80ºC; f, Hot air drying at 80ºC after blanching.
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Moisture, protein, TS, AAM, SAM, IAM and WBC of yam flours
Sample
Protein
Moisture (g/100g)
(g/100g) c
77.52±0.48
(g/100g)
d
8.62±0.00
IAM
(g/100g) a
7.35±0.01
WBC
(g/100g) e
1.27±0.01
(g/100g) a
188.02±2.22a
H-40
12.29±0.39
BH-40
14.56±0.25d
0.44±0.00b
71.22±0.79b
10.31±0.00c
3.21±0.00b
7.10±0.00e
243.78±4.40c
H-60
9.69±0.00 b
1.86±0.02d
73.82±0.60c
11.08±0.01d
7.50±0.00f
3.58±0.01c
199.62±1.34a
BH-60
12.66±0.27c
0.20±0.00a
67.08±0.67a
11.89±0.01e
5.57±0.01c
6.32±0.01d
257.15±3.85d
H-80
5.86±0.68a
1.82±0.01c
67.96±0.56a
9.99±0.01b
7.17±0.01d
2.82±0.01b
219.04±7.99b
BH-80
9.36±0.58 b
0.20±0.00a
67.42±0.27a
12.66±0.01f
3.00±0.00a
9.66±0.01f
189.90±1.37a
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2.57±0.02
e
SAM
AAM
TS (g/100g)
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Values are means ± SD. Means with different letters in the same column differ significantly (P ≤ 0.05). TS, total
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starch; AAM, apparent amylose; SAM, soluble amylose; IAM, insoluble amylose; WBC, water-binding capacity;
H-40, Hot air drying at 40ºC; BH-40, Hot air drying at 40ºC after blanching; H-60, Hot air drying at 60ºC; BH-60,
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Table 2
Swelling power and solubility at different temperatures of yam flours Swelling power (g/g) at different temperatures 50 ºC
60 ºC a
70 ºC
80 ºC
18.82±0.18
50 ºC d
60 ºC
70 ºC
30.15±0.80 c
6.64±0.07b
6.41±0.07b
11.39±0.04bc
12.19±0.14b
16.64±0.49d
15.23±0.10b
16.27±0.27b
18.05±0.08b
22.03±0.04b
ab
b
12.17±0.01
c
d
b
e
e
e
48.83±1.04e
BH-60
6.02±0.15b
5.19±0.09ab
7.35±0.15b
7.61±0.43a
15.02±0.43c
H-80
4.34±0.19a
5.20±0.22ab
5.23±0.19a
14.21±0.09c
19.43±0.53d
BH-80
5.00±0.08 ab
5.03±0.03ab
7.76±0.20b
8.79±0.27 ab
10.60±0.08a
13.10±0.13
28.51±0.49
30.51±0.41
20.29±0.10
90 ºC c
a
18.25±0.15
19.42±0.11
80 ºC c
5.41±0.09ab 4.11±0.07
18.22±0.18
c
BH-40 H-60
16.37±0.28
d
3.97±0.23
7.74±0.05
11.61±0.30
90 ºC bc
H-40
5.14±0.28
4.32±0.14
a
M AN U
3.67±0.16
a
Solubility (g/100g) at different temperatures
SC
Sample
43.15±0.65
11.81±0.19a
11.25±0.21a
13.49±0.43a
15.68±0.43a
24.30±0.16a
16.08±0.31d
22.49±0.69d
20.78±0.03d
23.66±0.34d
33.02±0.26d
14.57±0.16c
15.51±0.18b
16.74±0.11b
18.62±0.06b
25.29±0.16b
TE D
Values are means ± SD. Means with different letters in the same column differ significantly (P ≤ 0.05). H-40: Hot air drying at 40ºC; BH-40, Hot air drying at 40ºC after blanching; H-60, Hot air
AC C
EP
drying at 60ºC; BH-60, Hot air drying at 60ºC after blanching; H-80, Hot air drying at 80ºC; BH-80, Hot air drying at 80ºC after blanching.
ACCEPTED MANUSCRIPT
Infrared ratios of absorbance, relative crystallinity, RDS, SDS, and RS contents, GI and HI of yam flours IR ratio of absorbance RDS (%)
1.006316
23.88±2.65d
1.63±0.26b
0.951015
0.992825
14.28±0.84bc
0.952427
1.081862
1.001982
22.35±1.45d
BH-60
0.94113
0.960983
0.988167
12.10±1.02ab
H-80
0.949624
1.063488
0.997881
16.26±1.43c
BH-80
0.911749
0.983158
0.980698
9.35±0.38a
R995/1022
R1047/1035
H-40
0.957253
1.101653
BH-40
0.97586
H-60
SDS (%)
RS (%)
GI (%)
HI (%)
13.25±0.26b
62.63±0.48d
54.72±0.59b
27.34±1.07b
7.03±0.00d
17.21±0.50d
46.98±0.79b
69.81±0.60e
54.83±1.09e
2.16±0.00c
16.22±0.51c
55.44±2.02c
64.41±0.95c
44.98±1.74c
13.54±0.26e
17.34±0.00d
36.20±0.67a
81.76±0.67f
76.60±1.23f
0.72±0.00a
5.35±0.00a
61.89±1.97d
50.18±0.45a
19.07±0.81a
2.20±0.00c
19.58±0.26e
45.64±1.69b
66.25±0.48d
48.34±0.87d
SC
Relative crystallinity (%) R1047/1022
M AN U
Sample
RI PT
Table 3
TE D
Values are means ± SD. Means with different letters in the same column differ significantly (P ≤ 0.05). RDS, Rapidly digestible starch; SDS, Slowly digestible starch; RS, Resistant starch; GI, Glycemic index; HI, Hydrolysis index; H-40, Hot air drying at 40ºC; BH-40, Hot air drying at 40ºC after blanching; H-60, Hot air drying at 60ºC; BH-60, Hot air drying at 60ºC after blanching;
AC C
EP
H-80, Hot air drying at 80ºC; BH-80, Hot air drying at 80ºC after blanching.
ACCEPTED MANUSCRIPT
RI PT
Table 4
PPOPOD activities, allantoin, total flavones and total polyphenols contents, as well as antioxidant capacity of yam flours Total flavone
Total soluble polyphenol
DPPH scavenging activity
Reducing power
(mg RE/g)
(mg CE/g)
(EC50, mg/mL)
(µmol AC/g dw)
0.149±0.002d
0.49±0.00c
1.05±0.00e
87.00±0.96a
BH-40
0.066±0.003a
0.60±0.00f
0.70±0.00d
H-60
0.155±0.000e
0.38±0.00b
0.68±0.01c
BH-60
0.095±0.000c
0.58±0.00e
0.68±0.00 c
H-80
0.075±0.003b
0.35±0.00a
0.60±0.01b
BH-80
0.078±0.003b
0.50±0.00d
0.57±0.01a
H-40
PPO（AU/g•min）
POD（AU/g•min）
147.76±1.53e
0.028±0.003d
0.0020±0.0000d
111.10±0.80b
103.32±0.92b
0.004±0.000a
0.0007±0.0000b
142.50±0.82c
126.50±1.33d
0.024±0.001c
0.0012±0.0000c
106.45±0.87b
112.96±2.87c
0.005±0.000a
0.0007±0.0000b
189.15±0.18e
93.39±0.53a
0.015±0.001b
0.0011±0.0002c
158.15±0.27d
128.40±1.31d
0.007±0.000a
0.0003±0.0000a
SC
Allantoin (g/100g)
M AN U
Sample
TE D
Values are means ± SD. Means with different letters in the same column differ significantly (P ≤ 0.05). PPO, Polyphenol oxidase; POD, Peroxidase; H-40, Hot air drying at 40ºC; BH-40, Hot air
AC C
EP
drying at 40ºC after blanching; H-60, Hot air drying at 60ºC; BH-60, Hot air drying at 60ºC after blanching; H-80, Hot air drying at 80ºC; BH-80, Hot air drying at 80ºC after blanching.
ACCEPTED MANUSCRIPT Table 5
Pearson correlation coefficients for the relationship of TF, TSP, PPO, POD, EC50 and RP of yam flours TF
TSP
PPO
POD
TF
1
TSP
-.095
1
PPO
-.861**
.507
1
POD
-.736**
.694*
.868**
1
EC50
-.821**
-.292
.473
.371
RP
-.035
.684*
.496
.323
EC50
RP
RI PT
Parameter
1
-.376
1
SC
* P ≤ 0.05, ** P ≤ 0.01. TF, Total flavones; TSP, Total soluble polyphenols; PPO, polyphenol oxidase activity;
AC C
EP
TE D
M AN U
POD, peroxidase activity; EC50, DPPH scavenging activity; RP, Reducing power.
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
Fig.1
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
Fig.2
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
Fig.3
ACCEPTED MANUSCRIPT Highlights: Yam with hot air-drying at 60ºC had higher allantoin content. Yam with hot air-drying at 40ºC and 80ºC had higher resistant starch.
RI PT
Blanching (100ºC for 1min) was effective to inhibiting enzymatic browning of yam. Flavonoid ingredients of yam may be mainly substrate of enzymatic browning
AC C
EP
TE D
M AN U
SC
reaction.