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Preparation, physicochemical characterization and application of acetylated lotus rhizome starches
Accepted Manuscript Title: Preparation, Physicochemical Characterization and Application of Acetylated Lotus Rhizome Starches Author: Suling Sun Ganwei Zhang Chaoyang Ma PII: DOI: Reference:
S0144-8617(15)00719-5 http://dx.doi.org/doi:10.1016/j.carbpol.2015.07.090 CARP 10192
To appear in: Received date: Revised date: Accepted date:
16-2-2015 27-7-2015 28-7-2015
Please cite this article as: Sun, S., Zhang, G., and Ma, C.,Preparation, Physicochemical Characterization and Application of Acetylated Lotus Rhizome Starches, Carbohydrate Polymers (2015), http://dx.doi.org/10.1016/j.carbpol.2015.07.090 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.
Preparation, Physicochemical Characterization and Application of Acetylated
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Lotus Rhizome Starches
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Suling Sun1, Ganwei Zhang1*, Chaoyang Ma2
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Hubei Key Laboratory of Economic Forest Germplasm Improvement and Resources
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Comprehensive Utilization, Huanggang Normal University, 438000 Huanggang,
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China
State Key Laboratory of Food Science and Technology, School of Food Science and
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Technology, Jiangnan University, 214122 Wuxi, China
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10 Abstract
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characterized and used as food additives in puddings. The percentage content of the
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acetyl groups and degree of substitution increased linearly with the amount of acetic
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Acetylated lotus rhizome starches were prepared, physicochemically
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anhydride used.
The introduction of acetyl groups was confirmed via Fourier
transform infrared (FT-IR) spectroscopy. The values of the pasting parameters were lower for acetylated starch than for native starch. Acetylation was found to increase
the light transmittance (%), the freeze-thaw stability, the swelling power and the
18
solubility of the starch.
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acetylated lotus rhizome starches as food additives indicated that puddings produced
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from the modified starches with superior properties over those prepared from native
∗
Sensorial scores for puddings prepared using native and
Corresponding author, email: [email protected], fax: 86-0713-8833606
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starch.
22 Keywords: Lotus rhizome starch, acetylation, physicochemical properties, pudding
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1 Introduction Starch is a class of carbohydrate-based polymers composed of anhydroglucose
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(AGU) units that are linked together by alpha-1,4 and alpha-1,6 glucosidic bonds
47
(Sweedman, Tizzotti, Schafer & Gilbert, 2013).
48
limitations, such as low paste transparency, high paste temperature, high paste
49
viscosity, susceptibility to retrogradation, and syneresis of their gels and thus have
50
limited use for certain applications (Saartrat, Puttanlek, Rungsardthong & Uttapap,
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2005; Sodhi & Singh, 2005). In order to decrease these undesirable properties of
52
native starch and improve its properties, modified starches have been developed.
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Native starches have certain
Native starches can be modified through various techniques, including physical,
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chemical, and enzymatic methods, or combinations of these methods (Arijaje, Wang,
56 57 58
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Shinn, Shah & Proctor, 2014; Ashogbon & Akintayo, 2014; Dupuis, Liu & Yada, 2014; Kittisuban, Lee, Suphantharika & Hamaker, 2014; Martinez, Pico & Gomez, 2015; Martínez, Rosell & Gómez, 2014; Rolland-Sabaté et al., 2012).
Among these starch
modification methods, the acetylation technique was developed in 1865 (Golachowski,
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Zieba, Kapelko-Zeberska, Drozdz, Gryszkin & Grzechac, 2015; Schutzenberger,
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1865). This method is a chemical modification strategy in which the molecular
61
structure of the starch is altered via the conversion of the hydroxyl groups into acetate
62
ester groups (El Halal et al., 2015). The introduction of acetyl groups generally
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improves the physical and chemical properties of the modified starch over those of the
64
native form.
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enhance the clarity of pastes of the starch, provide the starch with stability against
66
retrogradation, and allow it to withstand freeze-thaw processes (Kalita, Kaushik &
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Mahanta, 2014). Various starches, such as corn starch (Singh, Kaur & Singh, 2004;
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Singh, Chawla & Singh, 2004), potato starch (Mbougueng, Tenin, Scher & Tchiégang,
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2012), barley starch (El Halal et al., 2015), wheat starch (Ackar, Subaric, Babic,
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Milicevic & Jozinovic, 2014), cassava starch (Rolland-Sabaté et al., 2012), rice starch
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(Kalita, Kaushik & Mahanta, 2014; Shon & Yoo, 2006) and many other kinds of
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starches (Betancur, Chel & Canizares, 1997; Nunez-Santiago, Bello-Perez & Tecante,
73
2004; Saartrat, Puttanlek, Rungsardthong & Uttapap, 2005; Varavinit, Anuntavuttikul
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& Shobsngob, 2000) have been acetylated and their physicochemical properties
75
investigated.
77 78 79
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However, there have been no reports on the preparation of acetylated
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For example, acetylation can lower the gelatinization temperature,
lotus rhizome starches.
The lotus plant (Nelumbo nucifera Gaertn.), an aquatic perennial from the family
Nelumbonaceae, is of significant economic importance and is widely cultivated in China, India, Japan and Australia (Cai, Cai, Man, Yang, Wang & Wei, 2014; Cai, Cai,
80
Man, Yang, Zhang & Wei, 2014; Man, Cai, Cai, Xu, Huai & Wei, 2012).
In addition,
81
starch can be extracted from lotus rhizomes.
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available in China and are marketed as part of the daily breakfast meal, fast food
83
products, traditional confectioneries as well as food additives, and they are especially
These starches are commercially
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popular among children and the elderly (Geng, Zongdao & Yimin, 2007; Man, Cai,
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Cai, Xu, Huai & Wei, 2012). The production of lotus rhizome starch is rising each
86
year in order to meet market demand. There have been various studies focusing on
87
the physicochemical properties of native lotus rhizome starches (Cai, Cai, Man, Yang,
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Wang & Wei, 2014; Geng, Zongdao & Yimin, 2007; Man, Cai, Cai, Xu, Huai & Wei,
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2012). With regard to the preparation of modified lotus rhizome starches, however,
90
there has been only a few reports describing methods involving acid treatment and
91
enzymatic degradation (Cai, Cai, Man, Yang, Zhang & Wei, 2014; Lin, Chang, Lin,
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Jane, Sheu & Lu, 2006). In addition, there have been no reports describing the
93
applications of modified lotus rhizome starches for food products or their relevance to
94
other fields.
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In this study, the lotus rhizome starches were acetylated with acetic anhydride,
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and the physicochemical properties of the acetylated lotus rhizome starches were
98 99 100
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subsequently investigated. The modified products were used as food additives for the preparation of puddings. The appearance and quality of the puddings were also evaluated by sensory analysis methods, and it was found that these modified starches enhanced the attractiveness of the resultant puddings.
101 102 103 104
2 Materials and methods 2.1 Materials Lotus (N. nucifera Gaertn.) plants were cultivated and the rhizomes were
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harvested in Huanggang, Hubei Province, China. Starch was isolated according to a
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procedure reported by Lin and coworkers (Lin, Chang, Lin, Jane, Sheu & Lu, 2006).
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Acetic anhydride (Aladdin, 99%) was of analytical grade and was distilled before use.
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Sodium hydroxide (Aladdin, 99%) and hydrochloric acid (Aladdin, 99%) were both
109
of analytical grade and used as received.
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2.2 Preparation of lotus rhizome starch acetate
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The method reported by Singh et al. was used to prepare the acetylated starches (Singh, Chawla & Singh, 2004).
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rhizome starch (containing 13.5 wt% water) was dispersed into 235 mL of distilled
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water in a 500 mL four-neck flask equipped with a mechanical stirrer. The mixture
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was stirred at room temperature for 3 h before a 3% (wt%) NaOH solution was added
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to adjust the pH of the suspension to 8.0. Acetic anhydride (2.03 g, ~2.0 wt% of dry
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starch) was slowly added dropwise into the starch slurry, while a 3% (wt%) NaOH
119 120 121
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In a typical procedure, 115.7 grams of lotus
an
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solution was used to keep the pH within the range of 8.0~8.4.
The reaction was
allowed to continue for 30 min after all of the acetic anhydride had been added. This reaction mixture was then adjusted to pH 6.5 with 0.1 M HCl. The mixture was subsequently centrifuged at 1917 g and the precipitate was obtained. The precipitate
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was dispersed in distilled water and centrifuged again.
The washing step was
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repeated three times and the final product was dried at 35 °C in an oven for 72 h. A
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series of products were prepared in this manner using various amounts of acetic
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anhydride (4.0, 6.0, 8.0, and 10.0 wt% of dry starch).
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2.3 Measurement of the degree of acetylation The percentage content of acetyl groups (acetyl %) in the final product and the
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degree of substitution (DS) achieved during the acetylation were determined
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according to Ogawa’s method (Ogawa et al., 1999). Starch acetate (5.0 g) was
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mixed with 50.0 mL of distilled water in a 250 mL flask.
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phenolphthalein were added into the suspension as an indicator, and then a 0.1 M
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NaOH solution was added until the solution exhibited a red color.
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stirred at room temperature for 30 min after 25.0 mL of a 0.45 M NaOH solution had
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been added.
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during the saponification reaction.
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titrated with a 0.2 M HCl solution until the indicator exhibited a colour change.
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blank test using native starch was also performed by following the same method.
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The percentage content of acetyl groups (acetyl %) in the modified starch (dry basis)
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Five drops of
an
The mixture was
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The flask was sealed to prevent evaporation of the produced acetate The final mixture containing excess alkali was
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A
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correspond to the molar concentration (in mol/L) of the HCl solution and the sample
144
weight in g (dry basis).
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was calculated according to the equation:
Acetyl % =
140 141
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(VB − VS ) × cHCl × 0.043 ×100 mS
Here, VB and VS correspond to the volume (in mL) of HCl used in the blank test
and in the sample titration, respectively.
The terms cHCl and mS respectively
The degree of substitution (DS) was calculated according to the equation:
7 Page 7 of 34
DS= 146
The DS can also be determined via 1H NMR characterization (Chi et al., 2008).
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The following equation could be used:
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(162 × Acetyl% ) ⎡⎣ 4300 − ( 42 × Acetyl% ) ⎤⎦
4A 3B + A
DS=
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where A denotes the sum of the integrations of the methyl protons at 2.01–2.08
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ppm; B denotes the sum of the integrations of the OH and H-1 protons for the
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anhydroglucose unit moiety observed above 4.5 ppm.
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2.4
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Infrared spectral analysis
FT-IR spectra were recorded using a Bruker FT-VERTEX 70 instrument at a
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scanning range of 400-4,000 cm-1, with a resolution of 2 cm-1. Native and acetylated
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lotus rhizome starches were mixed with KBr and pressed to form a KBr matrix prior
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to FT-IR characterization.
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2.5 NMR analysis
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The 1H NMR spectra were recorded using a Bruker AV400 spectrometer
(Ettlingen, Germany). Native or acetylated lotus rhizome starches were dissolved in DMSO-d6 at 75 °C to obtain clear solutions.
2.6 Size exclusion chromatography (SEC)
The
weight-average
molecular
weight
was
determined
using
a
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HPSEC-MALLS-RI system. The native and modified lotus rhizome starch samples
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(9.0 mg, dry basis) were thoroughly dissolved in 10.0 mL of DMSO with 50 mmol/L
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NaNO3
(4.25g NaNO3 was dissolved in 1.0 L DMSO) in boiling water under 8 Page 8 of 34
constant stirring for 2 h, and then continuously stirred at 25 °C for 24 h. The
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samples were filtered through a 0.45 μm organic filter before analysis. The system
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consisted of a pump (LC-20A, Shimadzu, Co., Kyoto, Japan), a MALLS detector
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(Dawn DSP, Wyatt Tech., Santa Barbara, CA, USA), and a RI detector (Waters 2414
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differential refractometer). The columns used were Styragel HMW7 and Styragel
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HMW6 columns (Styragel, Waters, Milford, MA) that were connected in series and
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kept at 40 °C. The mobile phase was DMSO with 50 mmol/L NaNO3 solution at a
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flow rate of 0.6 mL/min. Standard dextran samples (Sigma-Aldrich, St. Louis, MO,
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USA) with various molecular weights (Mw) were used for the Mw calibration.
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2.7 Pasting properties
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The pasting properties of the native and modified lotus rhizome starch samples
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were determined using a model RVA 3C Rapid Visco Analyser (Newport Scientific
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Pty Ltd, Warriewood, Australia).
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A sample of starch (2.15 g, dry basis) and a
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weighed amount of distilled water were mixed and stirred in an aluminum RVA sample container to produce an 8.0 wt% starch slurry. The test was developed according to the general pasting method (STD 2). The slurries were first kept at 50 °C for 1 min, heated to 95 °C within 7.5 min, kept at 95 °C for 5 min, cooled to
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50 °C within 7.5 min and subsequently kept at 50 °C for 2 min. This operation was
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performed in triplicate and the average values were reported.
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2.8 Transmittance (%)
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The light transmittance (%) of the native and modified lotus rhizome starches
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was measured by the method reported by Lawal (Lawal, 2004). Native and modified
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starch samples (0.40 g, dry basis) and 40 mL of distilled water were mixed together in
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50 mL test tubes that were plugged with cotton. These test tubes were subsequently
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heated and vigorously shaken in a boiling water bath for 30 min. After the samples
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had cooled to room temperature, the percentage transmittance (%) was determined at
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650 nm against a blank water sample with a Cary 100 spectrophotometer (Varian, Inc.
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Corporate, USA). In order to monitor the tendency for retrogradation, the samples
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were also stored at 4 °C and the percentage transmittance (%) was measured at 24 h
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intervals. This operation was repeated twice and the average value was reported.
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2.9 Freeze-thaw stability
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Freeze-thaw stabilities of the native and modified lotus rhizome starches were
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estimated according to the method reported by Varavinit (Varavinit, Anuntavuttikul &
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Shobsngob, 2000). A 30 g starch sample that had been dispersed into 470 mL of
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water was fully gelatinized at 90 °C for 30 min and was subsequently cooled to 25 °C. Common 50 mL plastic centrifuge tubes were accurately weighed and 25.00 g of the gelatinized starch paste was added into each of these tubes.
The tubes were
subsequently tightly capped and frozen at –18 °C for six days. All of the tubes were
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removed from the refrigerator and thawed at room temperature for 24 h. One of the
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tubes was centrifuged at 3,600 rpm for 15 min.
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subsequently removed and then the tube was weighed. The percentage of syneresis
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was then calculated as the ratio of the weight of the liquid decanted to the total weight
The clear supernatant was
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of the paste prior to centrifugation and multiplied by 100. The remaining tubes were
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then placed back in the freezer for further freeze-thaw cycling. Ten freeze-thaw
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cycles were performed in this case. In addition, another two batches of the paste
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from the same starch sample were subjected to the same procedure, and the reported
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syneresis value thus represents the average value obtained from the three experiments.
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2.10 Solubility and swelling power
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The swelling power and solubility of the starch samples were evaluated via triplicate
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(Nunez-Santiago, Bello-Perez & Tecante, 2004).
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placed into a 50 mL plastic centrifuge tube along with a magnetic stir bar. The
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mixture and the tube was weighed before 40 mL of distilled water was added into this
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tube. This sample slurry was then heated at 90 °C for 30 min under stirring. The
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supernatant was carefully collected via centrifugation at 3600 rpm for 15 min after the
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to
a
previously
reported
procedure
A starch sample (0.40 g) was
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according
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measurements
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mixture had cooled to room temperature and had been kept at this temperature for at least 30 min. This sample was subsequently dried overnight in an oven at 100 °C for 24 h in order to determine the mass of the soluble portion. The swollen starch sediment was also weighed after it had been fully dried. The solubility of the native
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or modified starch could be calculated as the mass ratio of the dried supernatant to
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that of the initial dry sample. In addition, the swelling power of the native or
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modified starch could be calculated as the number of grams of the swollen starch
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sediment per gram of the corresponding starch.
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2.11 Pudding sample preparation and sensory analysis
Pudding samples were prepared using native or acetylated lotus rhizome starches
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as additives. The recipe was modified according to a previously reported procedure
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(Gurmeric, Dogan, Toker, Senyigit & Ersoz, 2012). In a typical case, 20.0 g of corn
234
starch, 5.0 g of acetylated lotus rhizome starch (with an acetyl % value of 2.38 %) and
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1.0 g of vanilla were dispersed into 50.0 mL of milk at room temperature. This
236
mixture was then added to 450 mL of boiled milk containing 25 g of sugar. The
237
mixture was stirred for 1 min and then portions of this pudding were packaged in 25
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mL randomly coded glass containers.
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and stored in a refrigerator for 24 h prior to analysis. Pudding samples prepared
240
using different starch additives were all prepared a similar manner.
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The pudding was cooled to room temperature
The sensory analysis experiments were conducted by following a previously
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reported procedure (Gurmeric, Dogan, Toker, Senyigit & Ersoz, 2012). Initially,
244 245 246
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twelve undergraduate students were selected as panelists.
These students were
enrolled in the Food Science and Technology Specialty at our university, and they had all been provided training with sensory evaluation techniques in their specialty courses.
Further training was also provided to facilitate the evaluation of the
247
categories targeted in this study. The following quality attributes were used for the
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sensory evaluation of the prepared puddings (Alamri, Mohamed & Hussain, 2014;
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Ares, Baixauli, Sanz, Varela & Salvador, 2009): color, external thickness,
250
cohesiveness, melting behavior, smoothness, and general acceptability of the product.
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Further details of these six attributes are listed below. 1. Color: This attribute described the attractiveness of the sample in its initial
appearance.
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2.
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External thickness: The external thickness described the viscosity or the
ability of the product to flow, as evaluated visually as well as by manipulation of the
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product in the mouth. 3.
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Cohesiveness: This attribute related to the texture of the pudding.
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moderate value was targeted, since an excessively low cohesiveness would yield
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puddings with a too loose or runny texture that would readily break apart.
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Meanwhile, an excessively high value would indicate that the pudding had a
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rubber-like or overly firm texture.
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4. Melting behavior: This attribute described the length of time that the sample
retained its thickness in the mouth.
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5.
Smoothness: The smoothness described the presence or absence of
detectable particles in the pudding, and this factor ranged from gritty to smooth. This attribute was evaluated by pressing the sample against the roof of the mouth 6. General acceptability: This attribute evaluated the overall acceptability of the
product.
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At the beginning of this evaluation, the prepared pudding samples were
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randomly delivered to the panelists at 15 °C. The panelists gargled each sample
271
using warm water. The panelists were asked to score each sample according to the
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above quality attributes by completing a provided form. These evaluations were
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performed using a scale of ranging between 1 and 9, in which a value of 1 reflected a
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very low score and 9 indicated a very high score. The sensory data was processed
275
using the Senstools.NET v. 1.2.2.0 program to prepare an intuitive graph.
276 277
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3 Results and Discussion
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3.1 Preparation of the acetylated starches
Acetylation is an important method for modifying native starches, which can
280
endow starches with improved properties and broaden their range of applications.
281
Here, acetic anhydride was used to prepare acetylated lotus rhizome starch samples.
282
The effect of the amount of acetic anhydride used on the percentage content of the
283
acetyl groups (acetyl %) and the degree of substitution (DS) of the modified starch is
284
shown in Table 1.
286 287
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Table 1 Recipes and properties for the produced native and modified lotus rhizome
The amount of acetic anhydride (wt%)
starch samples.
Titration
NMR
Acetyl %
DS
DS
SEC Mw (g/mol)
0
---
---
---
4.04×107
2.0
0.70
0.027
0.029
3.67×107
4.0
1.47
0.056
0.060
3.55×107
6.0
1.91
0.073
0.076
3.07×107
8.0
2.38
0.092
0.097
2.60×107
10.0
2.61
0.101
0.105
2.50×107
14 Page 14 of 34
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--- The value was not statistically significant. The acetyl % and DS values that were determined via titration ranged from 0.70 to
290
2.61, and 0.027 to 0.101, respectively, and increased linearly with the acetic anhydride
291
contents. We noticed that the DS values of the acetylated lotus rhizome starches
292
were different from those observed among acetylated potato starches (Singh, Chawla
293
& Singh, 2004), acetylated corn starches (Singh, Chawla & Singh, 2004), acetylated
294
canna starches (Saartrat, Puttanlek, Rungsardthong & Uttapap, 2005), acetylated high-,
295
medium-, and low-amylose rice starches (Colussi et al., 2014), and acetylated yellow
296
pea starches (Huang, Schols, Jin, Sulmann & Voragen, 2007), prepared under similar
297
acetylation conditions.
298
different. Therefore, we can conclude that the DS values of acetylated starches are
299
determined not only by the type of reagent or the reaction conditions (Golachowski,
300
Zieba, Kapelko-Zeberska, Drozdz, Gryszkin & Grzechac, 2015), but also by the
302 303 304
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The DS values of these acetylated starches were also
Ac ce p
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botanical origin of the starches. As shown in Table 1, the DS values that were determined via 1H NMR spectroscopy were similar to those obtained via the titration
method. This consistency suggested indicated that both methods provided accurate data. The DS values determined via 1H NMR spectroscopy were slightly higher than
305
those determined via the titration method because the end units of the starch
306
molecular chain had four acetyl groups (Chi et al., 2008).
307
acetyl content limit permitted by the FDA for food starches is 2.5% ( Code of Federal
308
Regulations, 1994; Sodhi & Singh, 2005). Therefore, the use of 8.0 wt% acetic
The maximum
15 Page 15 of 34
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anhydride for the preparation protocol was advisable in our case (thus yielding starch
310
samples with an acetyl % value of 2.38, corresponding to a DS value of 0.092).
Fig. 1. FT-IR spectra of the native and modified lotus rhizome starches with different DS values (0.056 and 0.092).
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316 317 318 319
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The introduction of acetyl groups to the modified starches was also confirmed by
FT-IR analysis. Fig. 1 shows the FT-IR spectra of the native and modified starches bearing different DS values. The peak at 1731 cm-1 is attributed to the absorbance of the ester carbonyl of the acetyl moiety, while the peak at 1249 cm-1 corresponds to the
320
vibration absorbance of the C–O–C bonds between starch and the acetyl group. The
321
appearance of these two peaks in the modified starch as new signals that were not
322
observed in the native starch indicated that the acetyl groups were covalently bound to
323
the modified starch.
The peak intensity at 1731 and 1249 cm-1 increased when the
16 Page 16 of 34
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DS was changed from 0.056 to 0.092. Similar results have also been reported by
325
many
326
Mendez-Montealvo & Rodriguez-Ambriz, 2010; Chi et al., 2008; Mbougueng, Tenin,
327
Scher & Tchiégang, 2012; Sodhi & Singh, 2005). Therefore, FT-IR analysis also
328
provided a rapid and convenient method for evaluating the acetylation extent of the
329
modified starch samples.
researchers
(Bello-Pérez,
Agama-Acevedo,
Zamudio-Flores,
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other
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333 334 335 336
Fig. 2.
1
H NMR spectra of the native and modified lotus rhizome starches (a and c)
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with different degrees of substitution. The structure of acetylated lotus rhizome starch is also shown (b).
The introduction of acetyl groups to the modified starches was further verified by
337
1
H NMR analysis. Fig. 2a shows the 1H NMR spectra of the native and modified
338
starches at different degrees of substitution. In comparison to the spectrum of native
339
starch, new broad peaks at 2.01–2.08 ppm appeared in the spectrum of acetylated
340
lotus rhizome starches.
These peaks corresponded to the protons of the acetyl 17 Page 17 of 34
341
groups, and their integrations obviously increased when the DS value was changed
342
from 0.056 to 0.092.
343
different positions within the starch molecule were replaced by acetyl groups (Fig. 2b).
344
The methyl proton signals of the acetyl groups placed at C-6, C-2 and C-3 of the
345
native lotus rhizome starches were arranged according Kapelko’s report (Zięba,
346
Szumny & Kapelko, 2011), as shown in Fig. 2c. The signals corresponding to the
347
methyl protons of acetyl groups placed at C-6, C-2 and C-3 exhibited an integration
348
ratio of 10.5:5.5:0.9 (C-6:C-2:C-3) when the DS value was 0.092. Meanwhile, an
349
almost identical ratio of 10.7:5.3:1.0 was obtained when the DS value was 0.056.
350
This suggested that the acetylation reaction mainly occurred at the C-6 and C-2
351
positions of the lotus rhizome starch molecule in our case.
d
M
an
us
cr
ip t
The broad multiplet peak also indicated that protons at
The weight-averaged molecular weights (Mw) of native and acetylated lotus
353
rhizome starches were measured via HPSEC-MALLS-RI and the results are presented
355 356 357
Ac ce p
354
te
352
in Table 1. The Mw decreased with increases in the DS. This suggested that starch depolymerization had occurred during the process of acetylation, Similar results were also reported by many other researchers (Bello-Pérez, Agama-Acevedo, Zamudio-Flores, Mendez-Montealvo & Rodriguez-Ambriz, 2010; Berski et al., 2011;
358
Golachowski, Zieba, Kapelko-Zeberska, Drozdz, Gryszkin & Grzechac, 2015;
359
Lehmann & Volkert, 2009; Simsek, Ovando-Martinez, Whitney & Bello-Perez, 2012).
360
We must take note of two points regarding the HPSEC-MALLS-RI results. First, it
361
should be noted that the Mw value determined via SEC characterization likely
18 Page 18 of 34
differed from the actual molecular weight of the starch samples. The SEC system
363
was calibrated using a series of dextran samples, and thus the calibration provided the
364
relationship between the molecular weight and the hydrodynamic volumes of the
365
dextran standards, rather than starch.
366
hydrodynamic volume and molecular weight for dextran differs from that for the
367
starch samples, the SEC measurements thus did not provide an exact molecular
368
weight for the starch samples. Second, the decrease in the Mw was modest. The
369
Mw was 4.04×107 for the native starch, and 2.50×107 for the acetylated starch of DS =
370
0.101.
371
statistical
372
depolymerization should be slight.
373
3.2 Pasting properties of native and modified lotus rhizomerhizome starches
375 376 377 378
an
us
cr
Because this relationship between the
for
the
HPSEC-MALLS-RI
Considering a 10%
measurements,
the
starch
te
d
variation
M
The two numbers had the same order of magnitude.
The pasting properties of the native and acetylated lotus rhizome starches were
Ac ce p
374
ip t
362
investigated and the results are shown in Table 2. The pasting parameters, such as the peak viscosity, breakdown, final viscosity, setback and pasting temperature were lower for acetylated starch than for native starch. These differences indicated that the acetylation treatment could indeed change the pasting properties of the lotus
379
rhizome starches.
Similar results have also been reported by other researchers
380
(Simsek, Ovando-Martinez, Whitney & Bello-Perez, 2012). There are two factors
381
that may account for the low viscosity of the acetylated starches.
382
introduction of acetyl groups weakened and disintegrated the ordered structure of the
First, the
19 Page 19 of 34
native starch during the modification process (Saartrat, Puttanlek, Rungsardthong &
384
Uttapap, 2005). Second, the acetylation process resulted in depolymerization of the
385
starch samples, as we have descried earlier. The depolymerization resulted in a
386
reduction of the molecular weight and thus caused the viscosity to decrease. We also
387
found that there was a relatively weak correlation between the acetic anhydride
388
content and the viscosity parameters such as the viscosity, breakdown, final viscosity
389
and setback for the modified starches.
391 392 393
cr
us
an
Table 2. Pasting properties of native and acetylated lotus rhizome starches.
Breakdown (RVU)
Final viscosity (RVU)
Setback (RVU)
Pasting Temperature (°C)
---
614.7±1.4
451.8±0.7
323.1±1.3
160.3±0.9
68.6±1.0
0.027
556.0±05
389.0±2.1
264.0±0.7
97.0±0.5
66.3±1.3
0.056
560.6±0.8
405.7±0.6
256.7±1.1
101.8±1.9
64.6±0.8
0.073
581.5±1.1
397.8±0.1
275.9±2.3
92.2±0.6
63.8±0.3
0.092
543.8±0.9
388.9±0.5
241.2±1.1
86.3±0.7
62.9±0.7
0.101
583.0±0.3
405.2±1.6
278.8±0.7
101.1±0.3
62.0±1.7
te
d
M
DS
Peak viscosity (RVU)
Ac ce p
390
ip t
383
--- Native lotus rhizome starch. The pasting temperatures of the native and acetylated lotus rhizome starches
gradually decreased from 68.6 to 62.0 °C as the DS was increased. The low pasting
394
temperature of acetylated starches was also reported by many other researchers
395
(Lawal, 2004; Shon & Yoo, 2006; Singh, Kaur & Singh, 2004; Singh, Chawla &
396
Singh, 2004; Sodhi & Singh, 2005). The introduced acetyl moieties were distributed
397
throughout the granules and prevented the formation of hydrogen bonds between
20 Page 20 of 34
different starch molecules (Han, Liu, Gong, Lü, Ni & Zhang, 2012; Saartrat, Puttanlek,
399
Rungsardthong & Uttapap, 2005; Wani, Sogi & Gill, 2012), which allowed the
400
acetylated granules to swell and gelatinize more readily. Due to their improved
401
gelatinization behavior, the acetylated starches can potentially be processed at lower
402
temperatures, thus enhancing their potential for applications in the food industry.
403
3.3 Light transmittance (%) of native and modified lotus rhizome starches
us
cr
ip t
398
Acetylation can enhance the transparency of starch gels and improve the
405
appearance of starch-based foods by providing the surfaces of the foods with a glossy
406
appearance. Table 3 shows the changes in the light transmittance (%) of gels of the
407
modified starches that were observed as the DS was increased.
M
Table 3. Effect of the DS on the light transmittance (%) of gels of the modified lotus
d
408
an
404
rhizome starches. Transmittance at 640 nm (%)
Ac ce p
DS
te
409
410
0 days
3 days
5 days
10 days
20 days
30 days
---
39.7
33.2
32.7
31.9
26.5
23.3
0.027
50.3
44.1
43.1
41.2
40.2
38.2
0.056
61.2
56.3
55.6
54.9
52.1
47.6
0.073
70.1
66.3
65.2
64.8
63.2
61.2
0.092
78.9
75.3
74.8
73.2
73.1
72.5
0.101
83.2
82.8
82.2
81.5
81.3
80.2
--- Native lotus rhizome starch.
411
It was apparent that the light transmittance (%) increased with the DS, as shown
412
in Table 3. There were two kinds of explanations for this behavior. One is that the
413
introduction of acetyl groups can promote hydrogen bonding interactions between 21 Page 21 of 34
414
water molecules and the modified starch molecules (Betancur, Chel & Canizares,
415
1997), or influence water penetration and absorption on the starch granules and
416
ultimately enhance the swelling of the starch
417
Tchiégang, 2012), thus resulting in a higher light transmittance (%).
418
explanation is that the introduction of acetyl groups causes repulsions between
419
adjacent starch molecules and thus reduces interchain association, which resulted in
420
good light transmittance (%) (Han, Liu, Gong, Lü, Ni & Zhang, 2012; Wani, Sogi &
421
Gill, 2012).
422
the acetyl groups are not hydrophilic but hydrophobic. The light transmittance (%)
423
values of the gels of the starch samples generally decreased from their initial values
424
during storage. The light transmittance (%) values remained relatively high and
425
decreased only slightly by 3.6% over 30 days (from 83.2% to 80.2%) in the case of
426
the modified starches (with a DS of 0.101). In contrast, the light transmittance (%)
428 429 430 431
ip t
us
cr
Another
te
d
M
an
The latter explanation is more reasonable than the former one because
Ac ce p
427
(Mbougueng, Tenin, Scher &
values of the native lotus rhizome decreased dramatically by 41.3% from an initial value of 39.7% to 23.3% after 30 days. This behavior may have resulted from aggregation of the starch molecules, which was apparently inhibited by the acetylation treatment (Singh, Chawla & Singh, 2004).
3.4 Freeze-thaw stability of native and modified lotus rhizome starches
432
The ability of starch to withstand freezing and thawing without exhibiting
433
undesirable physical changes has been commonly known as “freeze–thaw” stability,
434
and this parameter can be used to evaluate the tendency of starch to retrograde
22 Page 22 of 34
(Yamazaki et al., 2013). When a starch gel is frozen, the formation of ice crystals
436
creates starch-rich regions in the gel matrix. In these starch-rich regions, the water
437
remains unfrozen and chain associations are facilitated. Upon thawing, bulk phase
438
water is easily released from the polymeric network, via a phenomenon known as
439
syneresis (Abd Karim, Norziah & Seow, 2000). Therefore, the amount of syneresis
440
exhibited by a starch sample has been assumed to be directly related to the tendency
441
of a starch to retrograde. In this research, the syneresis of the starch samples were
442
measured after various freeze-thaw cycles and the results of these experiments are
443
shown in Fig. 3.
444 445 446
Ac ce p
te
d
M
an
us
cr
ip t
435
Fig. 3.
Effect of freeze-thaw cycles on the gel syneresis behavior of native and modified lotus rhizome starches with different DS values.
447 448
Acetylation greatly changed the freeze-thaw stability of the starch samples, and
449
this was reflected by a decrease in the syneresis as the DS was increased. The 23 Page 23 of 34
syneresis observed after six freeze-thaw cycles decreased from 36% to 3% upon
451
progressing from native lotus rhizome starch to the modified starch with the highest
452
DS value of 0.101. In the cases of the modified starch samples with the DS values
453
of 0.092 and 0.101, no change in the syneresis (%) was observed after four
454
freeze-thaw cycles. The occurrence of syneresis in gels that had been subjected to
455
freeze-thaw treatment is attributed to a greater degree of molecular associations
456
between different starch chains (Saartrat, Puttanlek, Rungsardthong & Uttapap, 2005).
457
The significant reduction in syneresis that was observed after acetylation may be
458
attributed to inhibition of interactions between the starch molecules.
459
interactions occurred via hydrogen bonding between hydroxyl groups, which had
460
important roles in promoting the aggregation of the starch molecules. The inhibition
461
of the hydrogen bonding interactions between the starch molecules thus enhanced the
462
water-retaining capabilities of the hydroxyl groups. This ability of the acetylated
464 465 466
cr
us
an
te
d
M
These
Ac ce p
463
ip t
450
starch samples to resist syneresis has also been reported by many other researchers (Mbougueng, Tenin, Scher & Tchiégang, 2012; Saartrat, Puttanlek, Rungsardthong & Uttapap, 2005; Simsek, Ovando-Martinez, Whitney & Bello-Perez, 2012; Singh, Kaur & Singh, 2004; Singh, Chawla & Singh, 2004; Sodhi & Singh, 2005). Freezing is an
467
import method that is used in food processing and preservation, despite the fact that it
468
can cause serious structural damage to the food and alter its physical or textural
469
properties. Given the importance of freezing, minimizing the detrimental effects
470
induced by freezing and thawing have thus become vital yet challenging tasks in the
24 Page 24 of 34
food processing field.
Acetylation can endow starches with good freeze-thaw
472
stability, and this strategy thus has potential applications in the food industry.
473
3.5 Swelling power and solubility of native and modified lotus rhizome starches
ip t
471
When starch is heated in an excess amount of water, the starch polymer
475
molecules become solvated and both crystalline and amorphous structures are
476
disrupted. This phenomenon causes an increase in granule swelling and enhances
477
the solubility of the starch (Lee, Kumar, Rozman & Azemi, 2005). The swelling
478
power and solubility of the native and acetylated lotus rhizome starches were
479
investigated over a temperature range from 45 to 95 °C.
480
experiments are summarized in Fig. 4.
The results of these
481 482 483
Ac ce p
te
d
M
an
us
cr
474
Fig. 4. Swelling power and solubility of the native and modified lotus rhizome
starches.
484 485
The swelling power and solubility of native rhizome starches increased with the
486
temperature. The swelling power values ranged from 2.5 to 4.3 below 55 °C and
487
from 17.1 to 30.2 above 65 °C. The solubility values ranged from 1.4 to 1.8 below
25 Page 25 of 34
55 °C and from 3.1 to 9.5 above 65 °C. A similar increasing trend was observed
489
with regard to the swelling power and solubility of the acetylated lotus rhizome
490
starches. It was believed that an increase in the temperature weakened the hydrogen
491
bonding interactions between granules of native and modified starches and thus
492
improved their swelling power and solubility(Lawal & Adebowale, 2005).
493
shown in Fig. 4, the swelling power and solubility values of modified starches were
494
much larger than those of native starch samples. There are a number of possible
495
explanations for this behavior.
496
decreased after acetylation. This enhanced the swelling and solubility values of the
497
acetylated starches in comparison with those of the native starch samples at the same
498
temperature. Second, the introduction of acetyl groups to starch could disorganize
499
the intragranular structure and disrupt hydrogen bonds in the starch granules. This
500
situation would facilitate the access of water to amorphous domains of the acetylated
502 503 504
us
cr
As
te
d
M
an
First, the pasting temperatures of the starches
Ac ce p
501
ip t
488
starches (Wani, Sogi & Gill, 2012). Third, starch depolymerization occurred during acetylation, and consequently the acetylated starches were more readily swollen and solubilized in water.
3.6 Sensory analysis of the Pudding Samples
505
Pudding samples were prepared using native or acetylated lotus rhizome starches
506
as ingredients. Sensory analysis, including assessments of the appearance, taste or
507
smell, consistency in the mouth, consistency of the appearance, adhesiveness and
508
general acceptability, were conducted to evaluate the potential applicability of the
26 Page 26 of 34
509
acetylated starches as pudding ingredients.
510
samples are shown in Fig. 5.
The sensory scores of the pudding
d
M
an
us
cr
ip t
511
514 515 516 517
Fig. 5. Sensory scores of the pudding samples prepared using different lotus
Ac ce p
513
te
512
rhizome starches as additives.
As mentioned above, the acetylated lotus rhizome starches had good paste
transparency, swelling power, solubility and freeze-thaw stability. These modified
518
starches can endow the food product with good appearance and quality when applied
519
in the food industry.
520
prepare puddings, the resultant puddings exhibited much better appearance and
521
quality than was observed among the puddings prepared using native lotus rhizome
When the acetylated lotus rhizome starches were used to
27 Page 27 of 34
starch. The scores shown in Fig. 5 support this conclusion.
Across a wide range of
523
parameters, sensorial scores increased with the DS of the modified lotus rhizome
524
starches. As mentioned earlier, the maximum acetyl content permitted by the FDA
525
is 2.5% (Code of Federal Regulations, 1994; Sodhi & Singh, 2005). The modified
526
lotus rhizome starch with a DS value of 0.092 was within this limit and would thus be
527
suitable for use as an additive for the preparation of puddings. Conclusions
us
528
cr
ip t
522
In summary, we have reported the preparation and physicochemical
530
characterization of acetylated lotus rhizome starches as well as a preliminary
531
investigation their applications as additives in puddings. The introduction of acetyl
532
moieties to lotus rhizome starches yielded increases in paste transparency, swelling
533
power, solubility, and the freeze-thaw stability, while also providing decreases in the
534
pasting temperature, paste viscosity and syneresis. It was shown that puddings could
536 537 538
M
d
te
Ac ce p
535
an
529
be prepared with acetylated lotus rhizome starch. Sensory analysis demonstrated that these acetylated starches provided the pudding samples with good appearance and quality. Acetylation could thus endow lotus rhizome starch with superior physical and chemical properties, and this strategy thus has strong potential for application in
539
the food industry.
In addition to puddings, this modified starch has excellent
540
potential as an additive for a wide range of foods, such as fruit jelly, soups, noodles,
541
and various other foods.
542
28 Page 28 of 34
543 544
Acknowledgements.
545
Foundation and Doctoral Foundation of Huanggang Normal University (No
546
2011CB082, 2012015603, 2013016803, 10CB145). We also thank Dr. Ian Wyman
547
for revising this manuscript.
cr
ip t
We thank the financial support by the Natural Science
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Simsek, S., Ovando-Martinez, M., Whitney, K., & Bello-Perez, L. A. (2012). Effect of acetylation, oxidation and annealing on physicochemical properties of bean starch. Food Chemistry, 134(4), 1796-1803.
Singh, J., Kaur, L., & Singh, N. (2004). Effect of Acetylation on Some Properties of Corn and Potato Starches. Starch - Stärke, 56(12), 586-601.
Singh, N., Chawla, D., & Singh, J. (2004). Influence of acetic anhydride on physicochemical, morphological and thermal properties of corn and potato starch. Food Chemistry, 86(4), 601-608. Sodhi, N. S., & Singh, N. (2005). Characteristics of acetylated starches prepared using starches separated from different rice cultivars. Journal of Food Engineering, 70(1), 117-127. Sweedman, M. C., Tizzotti, M. J., Schafer, C., & Gilbert, R. G. (2013). Structure and physicochemical properties of octenyl succinic anhydride modified starches: a review. Carbohydrate Polymers, 92(1), 905-920. Varavinit, S., Anuntavuttikul, S., & Shobsngob, S. (2000). Influence of freezing and thawing
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techniques on stability of sago and tapioca starch pastes. Starch - Stärke, 52(6-7), 214-217. Wani, I. A., Sogi, D. S., & Gill, B. S. (2012). Physicochemical properties of acetylated starches from some Indian kidney bean (Phaseolus vulgaris L.) cultivars. International Journal of Food Science & Technology, 47(9), 1993-1999. Yamazaki, E., Sago, T., Kasubuchi, Y., Imamura, K., Matsuoka, T., Kurita, O., Nambu, H., & Matsumura, Y. (2013). Improvement on the freeze-thaw stability of corn starch gel by the
ip t
polysaccharide from leaves of Corchorus olitorius L. Carbohydrate Polymers, 94(1), 555-560.
Zięba, T., Szumny, A., & Kapelko, M. (2011). Properties of retrograded and acetylated starch preparations: Part 1. Structure, susceptibility to amylase, and pasting characteristics. LWT - Food Science and Technology, 44(5), 1314-1320.
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Preparation, Physicochemical Characterization and Application of
702
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Acetylated
Lotus Rhizome Starches
Suling Sun1, Ganwei Zhang1*, Chaoyang Ma2
1
Hubei Key Laboratory of Economic Forest Germplasm Improvement and
707
Resources Comprehensive Utilization, Huanggang Normal University, 438000
708
Huanggang, China
709 710
2
State Key Laboratory of Food Science and Technology, School of Food Science and Technology, Jiangnan University, 214122 Wuxi, China
33 Page 33 of 34
711 712
Highlights:
715
Acetylated lotus rhizome starches were prepared and physicochemically characterized.
cr
714
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The properties were greatly improved after acetylation.
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Acetylated lotus rhizome starches could be used as food additives in puddings.
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34 Page 34 of 34
S0144-8617(15)00719-5 http://dx.doi.org/doi:10.1016/j.carbpol.2015.07.090 CARP 10192
To appear in: Received date: Revised date: Accepted date:
16-2-2015 27-7-2015 28-7-2015
Please cite this article as: Sun, S., Zhang, G., and Ma, C.,Preparation, Physicochemical Characterization and Application of Acetylated Lotus Rhizome Starches, Carbohydrate Polymers (2015), http://dx.doi.org/10.1016/j.carbpol.2015.07.090 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.
Preparation, Physicochemical Characterization and Application of Acetylated
2
Lotus Rhizome Starches
3
Suling Sun1, Ganwei Zhang1*, Chaoyang Ma2
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1
4 1
Hubei Key Laboratory of Economic Forest Germplasm Improvement and Resources
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Comprehensive Utilization, Huanggang Normal University, 438000 Huanggang,
7
China
State Key Laboratory of Food Science and Technology, School of Food Science and
an
2
9
Technology, Jiangnan University, 214122 Wuxi, China
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8
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10 Abstract
12
characterized and used as food additives in puddings. The percentage content of the
13
acetyl groups and degree of substitution increased linearly with the amount of acetic
15 16 17
te
Ac ce p
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Acetylated lotus rhizome starches were prepared, physicochemically
d
11
anhydride used.
The introduction of acetyl groups was confirmed via Fourier
transform infrared (FT-IR) spectroscopy. The values of the pasting parameters were lower for acetylated starch than for native starch. Acetylation was found to increase
the light transmittance (%), the freeze-thaw stability, the swelling power and the
18
solubility of the starch.
19
acetylated lotus rhizome starches as food additives indicated that puddings produced
20
from the modified starches with superior properties over those prepared from native
∗
Sensorial scores for puddings prepared using native and
Corresponding author, email: [email protected], fax: 86-0713-8833606
1
Page 1 of 34
21
starch.
22 Keywords: Lotus rhizome starch, acetylation, physicochemical properties, pudding
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1 Introduction Starch is a class of carbohydrate-based polymers composed of anhydroglucose
46
(AGU) units that are linked together by alpha-1,4 and alpha-1,6 glucosidic bonds
47
(Sweedman, Tizzotti, Schafer & Gilbert, 2013).
48
limitations, such as low paste transparency, high paste temperature, high paste
49
viscosity, susceptibility to retrogradation, and syneresis of their gels and thus have
50
limited use for certain applications (Saartrat, Puttanlek, Rungsardthong & Uttapap,
51
2005; Sodhi & Singh, 2005). In order to decrease these undesirable properties of
52
native starch and improve its properties, modified starches have been developed.
cr
45
d
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an
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Native starches have certain
Native starches can be modified through various techniques, including physical,
54
chemical, and enzymatic methods, or combinations of these methods (Arijaje, Wang,
56 57 58
Ac ce p
55
te
53
Shinn, Shah & Proctor, 2014; Ashogbon & Akintayo, 2014; Dupuis, Liu & Yada, 2014; Kittisuban, Lee, Suphantharika & Hamaker, 2014; Martinez, Pico & Gomez, 2015; Martínez, Rosell & Gómez, 2014; Rolland-Sabaté et al., 2012).
Among these starch
modification methods, the acetylation technique was developed in 1865 (Golachowski,
59
Zieba, Kapelko-Zeberska, Drozdz, Gryszkin & Grzechac, 2015; Schutzenberger,
60
1865). This method is a chemical modification strategy in which the molecular
61
structure of the starch is altered via the conversion of the hydroxyl groups into acetate
62
ester groups (El Halal et al., 2015). The introduction of acetyl groups generally
3 Page 3 of 34
63
improves the physical and chemical properties of the modified starch over those of the
64
native form.
65
enhance the clarity of pastes of the starch, provide the starch with stability against
66
retrogradation, and allow it to withstand freeze-thaw processes (Kalita, Kaushik &
67
Mahanta, 2014). Various starches, such as corn starch (Singh, Kaur & Singh, 2004;
68
Singh, Chawla & Singh, 2004), potato starch (Mbougueng, Tenin, Scher & Tchiégang,
69
2012), barley starch (El Halal et al., 2015), wheat starch (Ackar, Subaric, Babic,
70
Milicevic & Jozinovic, 2014), cassava starch (Rolland-Sabaté et al., 2012), rice starch
71
(Kalita, Kaushik & Mahanta, 2014; Shon & Yoo, 2006) and many other kinds of
72
starches (Betancur, Chel & Canizares, 1997; Nunez-Santiago, Bello-Perez & Tecante,
73
2004; Saartrat, Puttanlek, Rungsardthong & Uttapap, 2005; Varavinit, Anuntavuttikul
74
& Shobsngob, 2000) have been acetylated and their physicochemical properties
75
investigated.
77 78 79
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However, there have been no reports on the preparation of acetylated
Ac ce p
76
For example, acetylation can lower the gelatinization temperature,
lotus rhizome starches.
The lotus plant (Nelumbo nucifera Gaertn.), an aquatic perennial from the family
Nelumbonaceae, is of significant economic importance and is widely cultivated in China, India, Japan and Australia (Cai, Cai, Man, Yang, Wang & Wei, 2014; Cai, Cai,
80
Man, Yang, Zhang & Wei, 2014; Man, Cai, Cai, Xu, Huai & Wei, 2012).
In addition,
81
starch can be extracted from lotus rhizomes.
82
available in China and are marketed as part of the daily breakfast meal, fast food
83
products, traditional confectioneries as well as food additives, and they are especially
These starches are commercially
4 Page 4 of 34
popular among children and the elderly (Geng, Zongdao & Yimin, 2007; Man, Cai,
85
Cai, Xu, Huai & Wei, 2012). The production of lotus rhizome starch is rising each
86
year in order to meet market demand. There have been various studies focusing on
87
the physicochemical properties of native lotus rhizome starches (Cai, Cai, Man, Yang,
88
Wang & Wei, 2014; Geng, Zongdao & Yimin, 2007; Man, Cai, Cai, Xu, Huai & Wei,
89
2012). With regard to the preparation of modified lotus rhizome starches, however,
90
there has been only a few reports describing methods involving acid treatment and
91
enzymatic degradation (Cai, Cai, Man, Yang, Zhang & Wei, 2014; Lin, Chang, Lin,
92
Jane, Sheu & Lu, 2006). In addition, there have been no reports describing the
93
applications of modified lotus rhizome starches for food products or their relevance to
94
other fields.
d
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us
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84
In this study, the lotus rhizome starches were acetylated with acetic anhydride,
96
and the physicochemical properties of the acetylated lotus rhizome starches were
98 99 100
Ac ce p
97
te
95
subsequently investigated. The modified products were used as food additives for the preparation of puddings. The appearance and quality of the puddings were also evaluated by sensory analysis methods, and it was found that these modified starches enhanced the attractiveness of the resultant puddings.
101 102 103 104
2 Materials and methods 2.1 Materials Lotus (N. nucifera Gaertn.) plants were cultivated and the rhizomes were
5 Page 5 of 34
harvested in Huanggang, Hubei Province, China. Starch was isolated according to a
106
procedure reported by Lin and coworkers (Lin, Chang, Lin, Jane, Sheu & Lu, 2006).
107
Acetic anhydride (Aladdin, 99%) was of analytical grade and was distilled before use.
108
Sodium hydroxide (Aladdin, 99%) and hydrochloric acid (Aladdin, 99%) were both
109
of analytical grade and used as received.
110
2.2 Preparation of lotus rhizome starch acetate
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111
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105
The method reported by Singh et al. was used to prepare the acetylated starches (Singh, Chawla & Singh, 2004).
113
rhizome starch (containing 13.5 wt% water) was dispersed into 235 mL of distilled
114
water in a 500 mL four-neck flask equipped with a mechanical stirrer. The mixture
115
was stirred at room temperature for 3 h before a 3% (wt%) NaOH solution was added
116
to adjust the pH of the suspension to 8.0. Acetic anhydride (2.03 g, ~2.0 wt% of dry
117
starch) was slowly added dropwise into the starch slurry, while a 3% (wt%) NaOH
119 120 121
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118
In a typical procedure, 115.7 grams of lotus
an
112
solution was used to keep the pH within the range of 8.0~8.4.
The reaction was
allowed to continue for 30 min after all of the acetic anhydride had been added. This reaction mixture was then adjusted to pH 6.5 with 0.1 M HCl. The mixture was subsequently centrifuged at 1917 g and the precipitate was obtained. The precipitate
122
was dispersed in distilled water and centrifuged again.
The washing step was
123
repeated three times and the final product was dried at 35 °C in an oven for 72 h. A
124
series of products were prepared in this manner using various amounts of acetic
125
anhydride (4.0, 6.0, 8.0, and 10.0 wt% of dry starch).
6 Page 6 of 34
126
2.3 Measurement of the degree of acetylation The percentage content of acetyl groups (acetyl %) in the final product and the
128
degree of substitution (DS) achieved during the acetylation were determined
129
according to Ogawa’s method (Ogawa et al., 1999). Starch acetate (5.0 g) was
130
mixed with 50.0 mL of distilled water in a 250 mL flask.
131
phenolphthalein were added into the suspension as an indicator, and then a 0.1 M
132
NaOH solution was added until the solution exhibited a red color.
133
stirred at room temperature for 30 min after 25.0 mL of a 0.45 M NaOH solution had
134
been added.
135
during the saponification reaction.
136
titrated with a 0.2 M HCl solution until the indicator exhibited a colour change.
137
blank test using native starch was also performed by following the same method.
138
The percentage content of acetyl groups (acetyl %) in the modified starch (dry basis)
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127
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Five drops of
an
The mixture was
M
The flask was sealed to prevent evaporation of the produced acetate The final mixture containing excess alkali was
142
Ac ce p
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d
A
143
correspond to the molar concentration (in mol/L) of the HCl solution and the sample
144
weight in g (dry basis).
139
was calculated according to the equation:
Acetyl % =
140 141
145
(VB − VS ) × cHCl × 0.043 ×100 mS
Here, VB and VS correspond to the volume (in mL) of HCl used in the blank test
and in the sample titration, respectively.
The terms cHCl and mS respectively
The degree of substitution (DS) was calculated according to the equation:
7 Page 7 of 34
DS= 146
The DS can also be determined via 1H NMR characterization (Chi et al., 2008).
147
The following equation could be used:
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148
(162 × Acetyl% ) ⎡⎣ 4300 − ( 42 × Acetyl% ) ⎤⎦
4A 3B + A
DS=
150
where A denotes the sum of the integrations of the methyl protons at 2.01–2.08
151
ppm; B denotes the sum of the integrations of the OH and H-1 protons for the
152
anhydroglucose unit moiety observed above 4.5 ppm.
153
2.4
an
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Infrared spectral analysis
FT-IR spectra were recorded using a Bruker FT-VERTEX 70 instrument at a
155
scanning range of 400-4,000 cm-1, with a resolution of 2 cm-1. Native and acetylated
156
lotus rhizome starches were mixed with KBr and pressed to form a KBr matrix prior
157
to FT-IR characterization.
158
2.5 NMR analysis
160 161 162 163
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The 1H NMR spectra were recorded using a Bruker AV400 spectrometer
(Ettlingen, Germany). Native or acetylated lotus rhizome starches were dissolved in DMSO-d6 at 75 °C to obtain clear solutions.
2.6 Size exclusion chromatography (SEC)
The
weight-average
molecular
weight
was
determined
using
a
164
HPSEC-MALLS-RI system. The native and modified lotus rhizome starch samples
165
(9.0 mg, dry basis) were thoroughly dissolved in 10.0 mL of DMSO with 50 mmol/L
166
NaNO3
(4.25g NaNO3 was dissolved in 1.0 L DMSO) in boiling water under 8 Page 8 of 34
constant stirring for 2 h, and then continuously stirred at 25 °C for 24 h. The
168
samples were filtered through a 0.45 μm organic filter before analysis. The system
169
consisted of a pump (LC-20A, Shimadzu, Co., Kyoto, Japan), a MALLS detector
170
(Dawn DSP, Wyatt Tech., Santa Barbara, CA, USA), and a RI detector (Waters 2414
171
differential refractometer). The columns used were Styragel HMW7 and Styragel
172
HMW6 columns (Styragel, Waters, Milford, MA) that were connected in series and
173
kept at 40 °C. The mobile phase was DMSO with 50 mmol/L NaNO3 solution at a
174
flow rate of 0.6 mL/min. Standard dextran samples (Sigma-Aldrich, St. Louis, MO,
175
USA) with various molecular weights (Mw) were used for the Mw calibration.
176
2.7 Pasting properties
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The pasting properties of the native and modified lotus rhizome starch samples
178
were determined using a model RVA 3C Rapid Visco Analyser (Newport Scientific
179
Pty Ltd, Warriewood, Australia).
181 182 183
te
A sample of starch (2.15 g, dry basis) and a
Ac ce p
180
d
177
weighed amount of distilled water were mixed and stirred in an aluminum RVA sample container to produce an 8.0 wt% starch slurry. The test was developed according to the general pasting method (STD 2). The slurries were first kept at 50 °C for 1 min, heated to 95 °C within 7.5 min, kept at 95 °C for 5 min, cooled to
184
50 °C within 7.5 min and subsequently kept at 50 °C for 2 min. This operation was
185
performed in triplicate and the average values were reported.
186
2.8 Transmittance (%)
187
The light transmittance (%) of the native and modified lotus rhizome starches
9 Page 9 of 34
was measured by the method reported by Lawal (Lawal, 2004). Native and modified
189
starch samples (0.40 g, dry basis) and 40 mL of distilled water were mixed together in
190
50 mL test tubes that were plugged with cotton. These test tubes were subsequently
191
heated and vigorously shaken in a boiling water bath for 30 min. After the samples
192
had cooled to room temperature, the percentage transmittance (%) was determined at
193
650 nm against a blank water sample with a Cary 100 spectrophotometer (Varian, Inc.
194
Corporate, USA). In order to monitor the tendency for retrogradation, the samples
195
were also stored at 4 °C and the percentage transmittance (%) was measured at 24 h
196
intervals. This operation was repeated twice and the average value was reported.
197
2.9 Freeze-thaw stability
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Freeze-thaw stabilities of the native and modified lotus rhizome starches were
199
estimated according to the method reported by Varavinit (Varavinit, Anuntavuttikul &
200
Shobsngob, 2000). A 30 g starch sample that had been dispersed into 470 mL of
202 203 204
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Ac ce p
201
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198
water was fully gelatinized at 90 °C for 30 min and was subsequently cooled to 25 °C. Common 50 mL plastic centrifuge tubes were accurately weighed and 25.00 g of the gelatinized starch paste was added into each of these tubes.
The tubes were
subsequently tightly capped and frozen at –18 °C for six days. All of the tubes were
205
removed from the refrigerator and thawed at room temperature for 24 h. One of the
206
tubes was centrifuged at 3,600 rpm for 15 min.
207
subsequently removed and then the tube was weighed. The percentage of syneresis
208
was then calculated as the ratio of the weight of the liquid decanted to the total weight
The clear supernatant was
10 Page 10 of 34
of the paste prior to centrifugation and multiplied by 100. The remaining tubes were
210
then placed back in the freezer for further freeze-thaw cycling. Ten freeze-thaw
211
cycles were performed in this case. In addition, another two batches of the paste
212
from the same starch sample were subjected to the same procedure, and the reported
213
syneresis value thus represents the average value obtained from the three experiments.
214
2.10 Solubility and swelling power
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215
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The swelling power and solubility of the starch samples were evaluated via triplicate
217
(Nunez-Santiago, Bello-Perez & Tecante, 2004).
218
placed into a 50 mL plastic centrifuge tube along with a magnetic stir bar. The
219
mixture and the tube was weighed before 40 mL of distilled water was added into this
220
tube. This sample slurry was then heated at 90 °C for 30 min under stirring. The
221
supernatant was carefully collected via centrifugation at 3600 rpm for 15 min after the
223 224 225
to
a
previously
reported
procedure
A starch sample (0.40 g) was
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according
Ac ce p
222
measurements
an
216
mixture had cooled to room temperature and had been kept at this temperature for at least 30 min. This sample was subsequently dried overnight in an oven at 100 °C for 24 h in order to determine the mass of the soluble portion. The swollen starch sediment was also weighed after it had been fully dried. The solubility of the native
226
or modified starch could be calculated as the mass ratio of the dried supernatant to
227
that of the initial dry sample. In addition, the swelling power of the native or
228
modified starch could be calculated as the number of grams of the swollen starch
229
sediment per gram of the corresponding starch.
11 Page 11 of 34
230
2.11 Pudding sample preparation and sensory analysis
Pudding samples were prepared using native or acetylated lotus rhizome starches
232
as additives. The recipe was modified according to a previously reported procedure
233
(Gurmeric, Dogan, Toker, Senyigit & Ersoz, 2012). In a typical case, 20.0 g of corn
234
starch, 5.0 g of acetylated lotus rhizome starch (with an acetyl % value of 2.38 %) and
235
1.0 g of vanilla were dispersed into 50.0 mL of milk at room temperature. This
236
mixture was then added to 450 mL of boiled milk containing 25 g of sugar. The
237
mixture was stirred for 1 min and then portions of this pudding were packaged in 25
238
mL randomly coded glass containers.
239
and stored in a refrigerator for 24 h prior to analysis. Pudding samples prepared
240
using different starch additives were all prepared a similar manner.
an
us
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231
d
M
The pudding was cooled to room temperature
The sensory analysis experiments were conducted by following a previously
242
reported procedure (Gurmeric, Dogan, Toker, Senyigit & Ersoz, 2012). Initially,
244 245 246
Ac ce p
243
te
241
twelve undergraduate students were selected as panelists.
These students were
enrolled in the Food Science and Technology Specialty at our university, and they had all been provided training with sensory evaluation techniques in their specialty courses.
Further training was also provided to facilitate the evaluation of the
247
categories targeted in this study. The following quality attributes were used for the
248
sensory evaluation of the prepared puddings (Alamri, Mohamed & Hussain, 2014;
249
Ares, Baixauli, Sanz, Varela & Salvador, 2009): color, external thickness,
250
cohesiveness, melting behavior, smoothness, and general acceptability of the product.
12 Page 12 of 34
251 252
Further details of these six attributes are listed below. 1. Color: This attribute described the attractiveness of the sample in its initial
appearance.
254
2.
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253
External thickness: The external thickness described the viscosity or the
ability of the product to flow, as evaluated visually as well as by manipulation of the
256
product in the mouth. 3.
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257
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255
Cohesiveness: This attribute related to the texture of the pudding.
A
moderate value was targeted, since an excessively low cohesiveness would yield
259
puddings with a too loose or runny texture that would readily break apart.
260
Meanwhile, an excessively high value would indicate that the pudding had a
261
rubber-like or overly firm texture.
264 265 266 267 268
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263
4. Melting behavior: This attribute described the length of time that the sample
retained its thickness in the mouth.
Ac ce p
262
an
258
5.
Smoothness: The smoothness described the presence or absence of
detectable particles in the pudding, and this factor ranged from gritty to smooth. This attribute was evaluated by pressing the sample against the roof of the mouth 6. General acceptability: This attribute evaluated the overall acceptability of the
product.
269
At the beginning of this evaluation, the prepared pudding samples were
270
randomly delivered to the panelists at 15 °C. The panelists gargled each sample
271
using warm water. The panelists were asked to score each sample according to the
13 Page 13 of 34
above quality attributes by completing a provided form. These evaluations were
273
performed using a scale of ranging between 1 and 9, in which a value of 1 reflected a
274
very low score and 9 indicated a very high score. The sensory data was processed
275
using the Senstools.NET v. 1.2.2.0 program to prepare an intuitive graph.
276 277
us
278
3 Results and Discussion
cr
ip t
272
3.1 Preparation of the acetylated starches
Acetylation is an important method for modifying native starches, which can
280
endow starches with improved properties and broaden their range of applications.
281
Here, acetic anhydride was used to prepare acetylated lotus rhizome starch samples.
282
The effect of the amount of acetic anhydride used on the percentage content of the
283
acetyl groups (acetyl %) and the degree of substitution (DS) of the modified starch is
284
shown in Table 1.
286 287
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Ac ce p
285
an
279
Table 1 Recipes and properties for the produced native and modified lotus rhizome
The amount of acetic anhydride (wt%)
starch samples.
Titration
NMR
Acetyl %
DS
DS
SEC Mw (g/mol)
0
---
---
---
4.04×107
2.0
0.70
0.027
0.029
3.67×107
4.0
1.47
0.056
0.060
3.55×107
6.0
1.91
0.073
0.076
3.07×107
8.0
2.38
0.092
0.097
2.60×107
10.0
2.61
0.101
0.105
2.50×107
14 Page 14 of 34
288
--- The value was not statistically significant. The acetyl % and DS values that were determined via titration ranged from 0.70 to
290
2.61, and 0.027 to 0.101, respectively, and increased linearly with the acetic anhydride
291
contents. We noticed that the DS values of the acetylated lotus rhizome starches
292
were different from those observed among acetylated potato starches (Singh, Chawla
293
& Singh, 2004), acetylated corn starches (Singh, Chawla & Singh, 2004), acetylated
294
canna starches (Saartrat, Puttanlek, Rungsardthong & Uttapap, 2005), acetylated high-,
295
medium-, and low-amylose rice starches (Colussi et al., 2014), and acetylated yellow
296
pea starches (Huang, Schols, Jin, Sulmann & Voragen, 2007), prepared under similar
297
acetylation conditions.
298
different. Therefore, we can conclude that the DS values of acetylated starches are
299
determined not only by the type of reagent or the reaction conditions (Golachowski,
300
Zieba, Kapelko-Zeberska, Drozdz, Gryszkin & Grzechac, 2015), but also by the
302 303 304
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an
M
te
d
The DS values of these acetylated starches were also
Ac ce p
301
ip t
289
botanical origin of the starches. As shown in Table 1, the DS values that were determined via 1H NMR spectroscopy were similar to those obtained via the titration
method. This consistency suggested indicated that both methods provided accurate data. The DS values determined via 1H NMR spectroscopy were slightly higher than
305
those determined via the titration method because the end units of the starch
306
molecular chain had four acetyl groups (Chi et al., 2008).
307
acetyl content limit permitted by the FDA for food starches is 2.5% ( Code of Federal
308
Regulations, 1994; Sodhi & Singh, 2005). Therefore, the use of 8.0 wt% acetic
The maximum
15 Page 15 of 34
309
anhydride for the preparation protocol was advisable in our case (thus yielding starch
310
samples with an acetyl % value of 2.38, corresponding to a DS value of 0.092).
Fig. 1. FT-IR spectra of the native and modified lotus rhizome starches with different DS values (0.056 and 0.092).
te
312 313 314
d
M
an
us
cr
ip t
311
316 317 318 319
Ac ce p
315
The introduction of acetyl groups to the modified starches was also confirmed by
FT-IR analysis. Fig. 1 shows the FT-IR spectra of the native and modified starches bearing different DS values. The peak at 1731 cm-1 is attributed to the absorbance of the ester carbonyl of the acetyl moiety, while the peak at 1249 cm-1 corresponds to the
320
vibration absorbance of the C–O–C bonds between starch and the acetyl group. The
321
appearance of these two peaks in the modified starch as new signals that were not
322
observed in the native starch indicated that the acetyl groups were covalently bound to
323
the modified starch.
The peak intensity at 1731 and 1249 cm-1 increased when the
16 Page 16 of 34
324
DS was changed from 0.056 to 0.092. Similar results have also been reported by
325
many
326
Mendez-Montealvo & Rodriguez-Ambriz, 2010; Chi et al., 2008; Mbougueng, Tenin,
327
Scher & Tchiégang, 2012; Sodhi & Singh, 2005). Therefore, FT-IR analysis also
328
provided a rapid and convenient method for evaluating the acetylation extent of the
329
modified starch samples.
researchers
(Bello-Pérez,
Agama-Acevedo,
Zamudio-Flores,
us
cr
ip t
other
331
333 334 335 336
Fig. 2.
1
H NMR spectra of the native and modified lotus rhizome starches (a and c)
Ac ce p
332
te
d
M
an
330
with different degrees of substitution. The structure of acetylated lotus rhizome starch is also shown (b).
The introduction of acetyl groups to the modified starches was further verified by
337
1
H NMR analysis. Fig. 2a shows the 1H NMR spectra of the native and modified
338
starches at different degrees of substitution. In comparison to the spectrum of native
339
starch, new broad peaks at 2.01–2.08 ppm appeared in the spectrum of acetylated
340
lotus rhizome starches.
These peaks corresponded to the protons of the acetyl 17 Page 17 of 34
341
groups, and their integrations obviously increased when the DS value was changed
342
from 0.056 to 0.092.
343
different positions within the starch molecule were replaced by acetyl groups (Fig. 2b).
344
The methyl proton signals of the acetyl groups placed at C-6, C-2 and C-3 of the
345
native lotus rhizome starches were arranged according Kapelko’s report (Zięba,
346
Szumny & Kapelko, 2011), as shown in Fig. 2c. The signals corresponding to the
347
methyl protons of acetyl groups placed at C-6, C-2 and C-3 exhibited an integration
348
ratio of 10.5:5.5:0.9 (C-6:C-2:C-3) when the DS value was 0.092. Meanwhile, an
349
almost identical ratio of 10.7:5.3:1.0 was obtained when the DS value was 0.056.
350
This suggested that the acetylation reaction mainly occurred at the C-6 and C-2
351
positions of the lotus rhizome starch molecule in our case.
d
M
an
us
cr
ip t
The broad multiplet peak also indicated that protons at
The weight-averaged molecular weights (Mw) of native and acetylated lotus
353
rhizome starches were measured via HPSEC-MALLS-RI and the results are presented
355 356 357
Ac ce p
354
te
352
in Table 1. The Mw decreased with increases in the DS. This suggested that starch depolymerization had occurred during the process of acetylation, Similar results were also reported by many other researchers (Bello-Pérez, Agama-Acevedo, Zamudio-Flores, Mendez-Montealvo & Rodriguez-Ambriz, 2010; Berski et al., 2011;
358
Golachowski, Zieba, Kapelko-Zeberska, Drozdz, Gryszkin & Grzechac, 2015;
359
Lehmann & Volkert, 2009; Simsek, Ovando-Martinez, Whitney & Bello-Perez, 2012).
360
We must take note of two points regarding the HPSEC-MALLS-RI results. First, it
361
should be noted that the Mw value determined via SEC characterization likely
18 Page 18 of 34
differed from the actual molecular weight of the starch samples. The SEC system
363
was calibrated using a series of dextran samples, and thus the calibration provided the
364
relationship between the molecular weight and the hydrodynamic volumes of the
365
dextran standards, rather than starch.
366
hydrodynamic volume and molecular weight for dextran differs from that for the
367
starch samples, the SEC measurements thus did not provide an exact molecular
368
weight for the starch samples. Second, the decrease in the Mw was modest. The
369
Mw was 4.04×107 for the native starch, and 2.50×107 for the acetylated starch of DS =
370
0.101.
371
statistical
372
depolymerization should be slight.
373
3.2 Pasting properties of native and modified lotus rhizomerhizome starches
375 376 377 378
an
us
cr
Because this relationship between the
for
the
HPSEC-MALLS-RI
Considering a 10%
measurements,
the
starch
te
d
variation
M
The two numbers had the same order of magnitude.
The pasting properties of the native and acetylated lotus rhizome starches were
Ac ce p
374
ip t
362
investigated and the results are shown in Table 2. The pasting parameters, such as the peak viscosity, breakdown, final viscosity, setback and pasting temperature were lower for acetylated starch than for native starch. These differences indicated that the acetylation treatment could indeed change the pasting properties of the lotus
379
rhizome starches.
Similar results have also been reported by other researchers
380
(Simsek, Ovando-Martinez, Whitney & Bello-Perez, 2012). There are two factors
381
that may account for the low viscosity of the acetylated starches.
382
introduction of acetyl groups weakened and disintegrated the ordered structure of the
First, the
19 Page 19 of 34
native starch during the modification process (Saartrat, Puttanlek, Rungsardthong &
384
Uttapap, 2005). Second, the acetylation process resulted in depolymerization of the
385
starch samples, as we have descried earlier. The depolymerization resulted in a
386
reduction of the molecular weight and thus caused the viscosity to decrease. We also
387
found that there was a relatively weak correlation between the acetic anhydride
388
content and the viscosity parameters such as the viscosity, breakdown, final viscosity
389
and setback for the modified starches.
391 392 393
cr
us
an
Table 2. Pasting properties of native and acetylated lotus rhizome starches.
Breakdown (RVU)
Final viscosity (RVU)
Setback (RVU)
Pasting Temperature (°C)
---
614.7±1.4
451.8±0.7
323.1±1.3
160.3±0.9
68.6±1.0
0.027
556.0±05
389.0±2.1
264.0±0.7
97.0±0.5
66.3±1.3
0.056
560.6±0.8
405.7±0.6
256.7±1.1
101.8±1.9
64.6±0.8
0.073
581.5±1.1
397.8±0.1
275.9±2.3
92.2±0.6
63.8±0.3
0.092
543.8±0.9
388.9±0.5
241.2±1.1
86.3±0.7
62.9±0.7
0.101
583.0±0.3
405.2±1.6
278.8±0.7
101.1±0.3
62.0±1.7
te
d
M
DS
Peak viscosity (RVU)
Ac ce p
390
ip t
383
--- Native lotus rhizome starch. The pasting temperatures of the native and acetylated lotus rhizome starches
gradually decreased from 68.6 to 62.0 °C as the DS was increased. The low pasting
394
temperature of acetylated starches was also reported by many other researchers
395
(Lawal, 2004; Shon & Yoo, 2006; Singh, Kaur & Singh, 2004; Singh, Chawla &
396
Singh, 2004; Sodhi & Singh, 2005). The introduced acetyl moieties were distributed
397
throughout the granules and prevented the formation of hydrogen bonds between
20 Page 20 of 34
different starch molecules (Han, Liu, Gong, Lü, Ni & Zhang, 2012; Saartrat, Puttanlek,
399
Rungsardthong & Uttapap, 2005; Wani, Sogi & Gill, 2012), which allowed the
400
acetylated granules to swell and gelatinize more readily. Due to their improved
401
gelatinization behavior, the acetylated starches can potentially be processed at lower
402
temperatures, thus enhancing their potential for applications in the food industry.
403
3.3 Light transmittance (%) of native and modified lotus rhizome starches
us
cr
ip t
398
Acetylation can enhance the transparency of starch gels and improve the
405
appearance of starch-based foods by providing the surfaces of the foods with a glossy
406
appearance. Table 3 shows the changes in the light transmittance (%) of gels of the
407
modified starches that were observed as the DS was increased.
M
Table 3. Effect of the DS on the light transmittance (%) of gels of the modified lotus
d
408
an
404
rhizome starches. Transmittance at 640 nm (%)
Ac ce p
DS
te
409
410
0 days
3 days
5 days
10 days
20 days
30 days
---
39.7
33.2
32.7
31.9
26.5
23.3
0.027
50.3
44.1
43.1
41.2
40.2
38.2
0.056
61.2
56.3
55.6
54.9
52.1
47.6
0.073
70.1
66.3
65.2
64.8
63.2
61.2
0.092
78.9
75.3
74.8
73.2
73.1
72.5
0.101
83.2
82.8
82.2
81.5
81.3
80.2
--- Native lotus rhizome starch.
411
It was apparent that the light transmittance (%) increased with the DS, as shown
412
in Table 3. There were two kinds of explanations for this behavior. One is that the
413
introduction of acetyl groups can promote hydrogen bonding interactions between 21 Page 21 of 34
414
water molecules and the modified starch molecules (Betancur, Chel & Canizares,
415
1997), or influence water penetration and absorption on the starch granules and
416
ultimately enhance the swelling of the starch
417
Tchiégang, 2012), thus resulting in a higher light transmittance (%).
418
explanation is that the introduction of acetyl groups causes repulsions between
419
adjacent starch molecules and thus reduces interchain association, which resulted in
420
good light transmittance (%) (Han, Liu, Gong, Lü, Ni & Zhang, 2012; Wani, Sogi &
421
Gill, 2012).
422
the acetyl groups are not hydrophilic but hydrophobic. The light transmittance (%)
423
values of the gels of the starch samples generally decreased from their initial values
424
during storage. The light transmittance (%) values remained relatively high and
425
decreased only slightly by 3.6% over 30 days (from 83.2% to 80.2%) in the case of
426
the modified starches (with a DS of 0.101). In contrast, the light transmittance (%)
428 429 430 431
ip t
us
cr
Another
te
d
M
an
The latter explanation is more reasonable than the former one because
Ac ce p
427
(Mbougueng, Tenin, Scher &
values of the native lotus rhizome decreased dramatically by 41.3% from an initial value of 39.7% to 23.3% after 30 days. This behavior may have resulted from aggregation of the starch molecules, which was apparently inhibited by the acetylation treatment (Singh, Chawla & Singh, 2004).
3.4 Freeze-thaw stability of native and modified lotus rhizome starches
432
The ability of starch to withstand freezing and thawing without exhibiting
433
undesirable physical changes has been commonly known as “freeze–thaw” stability,
434
and this parameter can be used to evaluate the tendency of starch to retrograde
22 Page 22 of 34
(Yamazaki et al., 2013). When a starch gel is frozen, the formation of ice crystals
436
creates starch-rich regions in the gel matrix. In these starch-rich regions, the water
437
remains unfrozen and chain associations are facilitated. Upon thawing, bulk phase
438
water is easily released from the polymeric network, via a phenomenon known as
439
syneresis (Abd Karim, Norziah & Seow, 2000). Therefore, the amount of syneresis
440
exhibited by a starch sample has been assumed to be directly related to the tendency
441
of a starch to retrograde. In this research, the syneresis of the starch samples were
442
measured after various freeze-thaw cycles and the results of these experiments are
443
shown in Fig. 3.
444 445 446
Ac ce p
te
d
M
an
us
cr
ip t
435
Fig. 3.
Effect of freeze-thaw cycles on the gel syneresis behavior of native and modified lotus rhizome starches with different DS values.
447 448
Acetylation greatly changed the freeze-thaw stability of the starch samples, and
449
this was reflected by a decrease in the syneresis as the DS was increased. The 23 Page 23 of 34
syneresis observed after six freeze-thaw cycles decreased from 36% to 3% upon
451
progressing from native lotus rhizome starch to the modified starch with the highest
452
DS value of 0.101. In the cases of the modified starch samples with the DS values
453
of 0.092 and 0.101, no change in the syneresis (%) was observed after four
454
freeze-thaw cycles. The occurrence of syneresis in gels that had been subjected to
455
freeze-thaw treatment is attributed to a greater degree of molecular associations
456
between different starch chains (Saartrat, Puttanlek, Rungsardthong & Uttapap, 2005).
457
The significant reduction in syneresis that was observed after acetylation may be
458
attributed to inhibition of interactions between the starch molecules.
459
interactions occurred via hydrogen bonding between hydroxyl groups, which had
460
important roles in promoting the aggregation of the starch molecules. The inhibition
461
of the hydrogen bonding interactions between the starch molecules thus enhanced the
462
water-retaining capabilities of the hydroxyl groups. This ability of the acetylated
464 465 466
cr
us
an
te
d
M
These
Ac ce p
463
ip t
450
starch samples to resist syneresis has also been reported by many other researchers (Mbougueng, Tenin, Scher & Tchiégang, 2012; Saartrat, Puttanlek, Rungsardthong & Uttapap, 2005; Simsek, Ovando-Martinez, Whitney & Bello-Perez, 2012; Singh, Kaur & Singh, 2004; Singh, Chawla & Singh, 2004; Sodhi & Singh, 2005). Freezing is an
467
import method that is used in food processing and preservation, despite the fact that it
468
can cause serious structural damage to the food and alter its physical or textural
469
properties. Given the importance of freezing, minimizing the detrimental effects
470
induced by freezing and thawing have thus become vital yet challenging tasks in the
24 Page 24 of 34
food processing field.
Acetylation can endow starches with good freeze-thaw
472
stability, and this strategy thus has potential applications in the food industry.
473
3.5 Swelling power and solubility of native and modified lotus rhizome starches
ip t
471
When starch is heated in an excess amount of water, the starch polymer
475
molecules become solvated and both crystalline and amorphous structures are
476
disrupted. This phenomenon causes an increase in granule swelling and enhances
477
the solubility of the starch (Lee, Kumar, Rozman & Azemi, 2005). The swelling
478
power and solubility of the native and acetylated lotus rhizome starches were
479
investigated over a temperature range from 45 to 95 °C.
480
experiments are summarized in Fig. 4.
The results of these
481 482 483
Ac ce p
te
d
M
an
us
cr
474
Fig. 4. Swelling power and solubility of the native and modified lotus rhizome
starches.
484 485
The swelling power and solubility of native rhizome starches increased with the
486
temperature. The swelling power values ranged from 2.5 to 4.3 below 55 °C and
487
from 17.1 to 30.2 above 65 °C. The solubility values ranged from 1.4 to 1.8 below
25 Page 25 of 34
55 °C and from 3.1 to 9.5 above 65 °C. A similar increasing trend was observed
489
with regard to the swelling power and solubility of the acetylated lotus rhizome
490
starches. It was believed that an increase in the temperature weakened the hydrogen
491
bonding interactions between granules of native and modified starches and thus
492
improved their swelling power and solubility(Lawal & Adebowale, 2005).
493
shown in Fig. 4, the swelling power and solubility values of modified starches were
494
much larger than those of native starch samples. There are a number of possible
495
explanations for this behavior.
496
decreased after acetylation. This enhanced the swelling and solubility values of the
497
acetylated starches in comparison with those of the native starch samples at the same
498
temperature. Second, the introduction of acetyl groups to starch could disorganize
499
the intragranular structure and disrupt hydrogen bonds in the starch granules. This
500
situation would facilitate the access of water to amorphous domains of the acetylated
502 503 504
us
cr
As
te
d
M
an
First, the pasting temperatures of the starches
Ac ce p
501
ip t
488
starches (Wani, Sogi & Gill, 2012). Third, starch depolymerization occurred during acetylation, and consequently the acetylated starches were more readily swollen and solubilized in water.
3.6 Sensory analysis of the Pudding Samples
505
Pudding samples were prepared using native or acetylated lotus rhizome starches
506
as ingredients. Sensory analysis, including assessments of the appearance, taste or
507
smell, consistency in the mouth, consistency of the appearance, adhesiveness and
508
general acceptability, were conducted to evaluate the potential applicability of the
26 Page 26 of 34
509
acetylated starches as pudding ingredients.
510
samples are shown in Fig. 5.
The sensory scores of the pudding
d
M
an
us
cr
ip t
511
514 515 516 517
Fig. 5. Sensory scores of the pudding samples prepared using different lotus
Ac ce p
513
te
512
rhizome starches as additives.
As mentioned above, the acetylated lotus rhizome starches had good paste
transparency, swelling power, solubility and freeze-thaw stability. These modified
518
starches can endow the food product with good appearance and quality when applied
519
in the food industry.
520
prepare puddings, the resultant puddings exhibited much better appearance and
521
quality than was observed among the puddings prepared using native lotus rhizome
When the acetylated lotus rhizome starches were used to
27 Page 27 of 34
starch. The scores shown in Fig. 5 support this conclusion.
Across a wide range of
523
parameters, sensorial scores increased with the DS of the modified lotus rhizome
524
starches. As mentioned earlier, the maximum acetyl content permitted by the FDA
525
is 2.5% (Code of Federal Regulations, 1994; Sodhi & Singh, 2005). The modified
526
lotus rhizome starch with a DS value of 0.092 was within this limit and would thus be
527
suitable for use as an additive for the preparation of puddings. Conclusions
us
528
cr
ip t
522
In summary, we have reported the preparation and physicochemical
530
characterization of acetylated lotus rhizome starches as well as a preliminary
531
investigation their applications as additives in puddings. The introduction of acetyl
532
moieties to lotus rhizome starches yielded increases in paste transparency, swelling
533
power, solubility, and the freeze-thaw stability, while also providing decreases in the
534
pasting temperature, paste viscosity and syneresis. It was shown that puddings could
536 537 538
M
d
te
Ac ce p
535
an
529
be prepared with acetylated lotus rhizome starch. Sensory analysis demonstrated that these acetylated starches provided the pudding samples with good appearance and quality. Acetylation could thus endow lotus rhizome starch with superior physical and chemical properties, and this strategy thus has strong potential for application in
539
the food industry.
In addition to puddings, this modified starch has excellent
540
potential as an additive for a wide range of foods, such as fruit jelly, soups, noodles,
541
and various other foods.
542
28 Page 28 of 34
543 544
Acknowledgements.
545
Foundation and Doctoral Foundation of Huanggang Normal University (No
546
2011CB082, 2012015603, 2013016803, 10CB145). We also thank Dr. Ian Wyman
547
for revising this manuscript.
cr
ip t
We thank the financial support by the Natural Science
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Preparation, Physicochemical Characterization and Application of
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Acetylated
Lotus Rhizome Starches
Suling Sun1, Ganwei Zhang1*, Chaoyang Ma2
1
Hubei Key Laboratory of Economic Forest Germplasm Improvement and
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Resources Comprehensive Utilization, Huanggang Normal University, 438000
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Huanggang, China
709 710
2
State Key Laboratory of Food Science and Technology, School of Food Science and Technology, Jiangnan University, 214122 Wuxi, China
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Highlights:
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Acetylated lotus rhizome starches were prepared and physicochemically characterized.
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The properties were greatly improved after acetylation.
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Acetylated lotus rhizome starches could be used as food additives in puddings.
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