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Structural and functional properties of starches from Chinese chestnuts
Food Hydrocolloids 43 (2015) 568e576
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Structural and functional properties of starches from Chinese chestnuts Chang Liu a, b, 1, Shujun Wang a, *, 1, Xuedong Chang b, Shuo Wang a, * a b
Key Laboratory of Food Nutrition and Safety, Ministry of Education, Tianjin University of Science & Technology, Tianjin 300457, China College of Food Science and Technology, Hebei Normal University of Science and Technology, Qinhuangdao City 066600, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 23 December 2013 Accepted 14 July 2014 Available online 22 July 2014
Structural and functional properties of starches isolated from four varieties of chestnuts grown in China were characterized in this study. The starch granules exhibited a variety of shapes, varying from round, croissant-like, irregular to triangular. The amylose content of four chestnut starches was about 21e22%. Average particle diameter of the four starches varied between 10.8 and 18.1 mm. The X-ray patterns of four chestnut starches were of C-type, with relative crystallinity ranging between 26 and 29%. Although there were only small differences between the starches in amylose content, they displayed significant variability in physicochemical and functional properties, such as swelling power, pasting characteristics, thermal and textural properties, freeze-thaw stability, and in susceptibility to in vitro attack by enzymes. Average particle diameter of four starch granules was negatively correlated with swelling power at 92.5 C (r ¼ 0.956, p < 0.05), and positively correlated with conclusion temperature in the DSC (r ¼ 0.988, p < 0.05). Correlation between swelling power at 92.5 C and conclusion temperature was also significant (r ¼ 0.973, p < 0.05). This study provides sufficient information on properties of Chinese chestnut starches, which would be very helpful for their application in food and other industries. © 2014 Elsevier Ltd. All rights reserved.
Keywords: Chestnut Starch Morphology Amylose Functional properties
1. Introduction The chestnut (Castanea mollissima Bl.), belonging to the Fagaceae family, is one of the major nuts in China. It has a growing history of over 2000 years in China and makes great contribution to the national economy. The chestnut fruit is considered a high nutritional value food and has long been used as one of the Traditional Chinese Medicines for health care in China (Zhang, Chen, & Zhang, 2011). Chestnut fruit is also an important and popular food, which is consumed widely throughout Europe, America, and Asia (De Vasconcelos, Bennett, Rosa, & FerreiraCardoso, 2010). As one of the oldest edible fruits in northern hemisphere, chestnut was consumed as extensively as potato in the past (Ferreira-Cardoso, Sequeira, Torres-Pereira, Rodrigues, & Gomes, 1999). Although chestnuts are mainly consumed freshly after roasting, boiling or stir-frying with syrup, some processed chestnut products need to be reheated before eating. There is increasing evidence showing that the consumption of chestnuts has become more and more important for human nutrition due to * Corresponding authors. E-mail addresses: [email protected] (S. Wang), [email protected] (S. Wang). 1 Equal contribution. http://dx.doi.org/10.1016/j.foodhyd.2014.07.014 0268-005X/© 2014 Elsevier Ltd. All rights reserved.
the health benefits provided by the presence of bioactive components, including lectin, cysteine proteinase inhibitor and quercetin (Blomhoff, Carlsen, Andersen, & Jacobs, 2006). The chemical composition of chestnuts boasts the highest content in polymeric carbohydrates, considerable levels of vitamins, fibres, and acceptable content in lipids and adequate minerals (Borges, Carvalho, rdez, & Queijeiro, 2004). Correia, & Silva, 2007; Miguelez, Berna Recently, chestnut has received much more attention, as can be seen from the increasing publications. On one hand, chestnut presents a large potential for commercial use since it is a good source of starch. On the other hand, the consumption of chestnut has been shown to have many nutritional benefits. Starch is the main storage carbohydrate of higher plants and the main source of energy in human diets. It is also a cheap raw material with distinct physiochemical properties that are very important for its application in food and non-food industries. Native starch is highly variable between and within plant species. This variability is evident in granular structure and functional properties (Wang, Sharp, & Copeland, 2011). The functional properties of starch granules include swelling power, starch solubility, gelatinization, retrogradation, syneresis, and rheological behaviour, which are generally determined by the multiple characteristics of starch structure.
C. Liu et al. / Food Hydrocolloids 43 (2015) 568e576
500 ml of 0.15% NaOH and settled for 2 h at 4 C. The supernatant was decanted, the sedimented starch was resuspended in 500 ml of deionized water, and the pH was adjusted to 6.5 with 0.1 M HCl. The starch suspension was allowed to sediment and the supernatant was discarded. The sedimented starch was washed several times with distilled water until the densely deposited white starch was obtained, and then freeze dried in a Freeze Dryer (LGJ-10 freeze drier, Four-Ring Science Instrument Plant Beijing Co. Lts, Beijing, China) at 50 C.
Table 1 Chemical composition of chestnut fruits. Varieties
Total starch content (%)a
Banhong Yanlong Yankui Zaofeng
44.8 42.4 50.8 53.8
± ± ± ±
0.8b 1.0b 1.7a 1.6a
Protein (%)a 9.5 8.9 7.7 8.5
± ± ± ±
0.3a 0.4 ab 0.3c 0.2bc
Lipid (%)a 2.1 2.3 2.3 2.4
± ± ± ±
0.1a 0.2a 0.1a 0.2a
Ash (%)a 1.9 2.0 2.2 2.3
± ± ± ±
569
0.1a 0.2a 0.2a 0.1a
Values are means ± SD. Means with the same letters in a column do not differ significantly (p < 0.05). a Dry weight basis.
2.3. Determination of the chemical composition of chestnuts and isolated starches
Starch is the main constituent of chestnut fruit. The starch content in chestnut fruit ranges from 38 to 80% (Borges, Gonçalves, Carvalho, Correia, & Silva, 2008; Miguelez et al., 2004). Although the structural and functional properties of chestnut starches have ~o-da-Costa, 2010; Correia, Cruz-Lopes, been studied (Correia & Beira ~o-da-Costa, 2012; Cruz, Abraa ~o, Lemos, & Nunes, 2013; & Beira Yang, Jiang, Prasad, Gu, & Jiang, 2010; Yoo, Lee, Kim, & Shin, 2012; Zhang et al., 2011), there have been few comparative studies on the properties of starches from Chinese chestnut varieties. To extend the application of chestnut, the knowledge on the functional properties of chestnut starch, including its susceptibility to the enzymatic digestion, is extremely important. As a result, one aim of the present study was to characterize the structural and functional properties of starches from four Chinese chestnut varieties and to analyze the relationships between these properties. Another important aim was to compare the functional properties of chestnut starches and commonly used corn starches for the potential utilization of chestnut starch in food and other industries.
Total and damaged starch content were determined using Megazyme Total Starch and Starch Damage Assay Kits (Megazyme International Ireland Ltd. Bray Co., Wicklow, Ireland), respectively. The analyses were performed according to the instructions supplied with the kits. Amylose content was determined by iodine binding method according to Williams, Kuzina, and Hlynka (1970). Nitrogen, lipid and ash content were determined according to AOAC official procedures (methods 954.01, 920.39 and 923.03) (AOAC, 1997). Protein content was obtained by multiplying the nitrogen content by 6.25. Moisture content was determined by oven drying of the starch at 105 C until constant weight (925.40 AOAC method) (AOAC, 2000). 2.4. Morphology of starch Chestnut starch was imaged using the SU-1510 Scanning Electron Microscope (Hitachi Company, Japan). Starch samples were mounted on a specimen holder using a double-sided carbon adhesive tape and sputter-coated with gold. An accelerating voltage of 5 kV was used during scanning.
2. Materials and methods 2.1. Samples Four Chinese chestnut varieties (Banhong, Zaofeng, Yanlong, Yankui) were obtained from chestnut storage and processing center of Hebei province, China. Yanlong is an advanced line from the breeding program of Hebei Normal University of Science and Technology. It was identified by Committee of Forestry Varieties of Hebei Province in 2009, and had Plant Breeders' Rights Application Number (S-SV-CM-003-2009). The chestnuts were grown and harvested at Yanshan Mountain in 2012 season. The harvested fruits were collected and stored at 4 C.
2.5. Particle size distribution
2.2. Starch extraction
X-ray diffraction analysis was performed using a D/max2500vk/pc X-ray diffractometer (Rigaku Corporation, Tokyo, Japan) operating at 40 V and 30 mA. Starches were equilibrated over a saturated potassium chloride (KCl) solution at room temperature for one week before analysis (Wang, Yu, Zhu, Yu, & Jin, 2009). The intensity was measured from 3 to 40 as a function of 2q and at a scanning speed of 1 /min and a step size of 0.02 . The degree of crystallinity was determined quantitatively following the n, & An ~o n, 2004). method reported previously (Ribotta, Cuffini, Leo The crystallinity of starch was calculated as a ratio of the crystalline
Particle size distribution of starch granules was measured using Laser Diffraction Particle Size Analyzer LA-920 (Horiba Instruments Ltd., Japan) according to the instructions supplied with the instrument. The starch was evenly dispersed in ethanol with magnetic agitation to attain a transmittance of 80%. 2.6. X-ray diffraction
Starch was isolated according to the method of Wang et al. (2011) with modifications as follows. The chestnuts (700 g) were rinsed, peeled and homogenized in a kitchen blender with 1.5 L distilled water for 1e2 min at maximum speed. The starch slurry was passed through a 140 mesh filtrating cloth. The resulting starch suspension was allowed to settle overnight at 4 C. The supernatant was decanted, and the brownish grey layer on top of the white starch sediment was removed. The starch pellet was dispersed in
Table 2 Chemical composition of chestnut starches. Varieties
Moisture (%)
Banhong Yanlong Yankui Zaofeng
5.52 5.23 5.70 5.93
± ± ± ±
0.24a 0.36a 0.11a 0.3 a
Protein (%)a 0.20 0.10 0.13 0.15
± ± ± ±
0.04a 0.03a 0.05a 0.06a
Lipid (%)a 0.79 0.62 0.73 0.65
± ± ± ±
0.08a 0.04a 0.06a 0.05a
Ash (%)a 0.07 0.10 0.14 0.09
± ± ± ±
0.02a 0.03a 0.05a 0.02a
Amylose (%) 21.16 21.80 22.27 21.67
Values are means ± SD. Means with the same letters in a column do not differ significantly (p < 0.05). a Dry weight basis.
± ± ± ±
0.38a 0.18a 0.25a 0.15a
Damage starch (%) 3.63 4.94 3.25 2.22
± ± ± ±
0.21b 0.28a 0.25c 0.10d
Mean particle size (mm) 12.68 10.76 12.52 18.10
± ± ± ±
0.05b 0.03c 0.06b 0.25a
570
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area to the total area using the JADE 5.0 software (Materials Data Inc, Livermore, CA, USA). 2.7. Swelling power Starch swelling power was determined in excess water at temperatures from 50 to 92.5 C according to the method of Konik-Rose et al. (2001) with some modifications (Wang & Copeland, 2012a). The water/starch ratio used in the swelling power test was 25:1, namely 1 mL water/40 mg starch. Starch swelling power was calculated as the ratio of the weight of the swollen starch to the initial dry weight of starch. 2.8. Syneresis The starch suspension (6%, w/v, dry weight basis) was heated for 30 min in a boiling water bath with constant stirring, and then the starch paste was transferred into a mould and cooled to 20 C. The syneresis of starch gels were measured at room temperature respectively. The other moulds were frozen in a chest freezer at 20 C for 22 h and then thawed at 30 C in a water bath for 2 h to reach an equilibration. Syneresis was measured as % amount of water released after centrifugation at 986 g for 20 min. The freezethaw cycle was repeated for up to 5 times to compare the freezethaw stability of chestnut starch gels. 2.9. Thermal properties Thermal properties of starches were studied using a differential scanning calorimeter (200 F3, Netzsch, Germany) equipped with a thermal analysis data station. The operating conditions of thermal transition were described elsewhere (Wang & Copeland, 2012b). Briefly, about 3 mg of starch were weighed into a 40 mL aluminium DSC crucibles, Distilled water was added to the starch in the DSC pans with a microsyringe to obtain a water:starch ration of 2:1 (w/ w). The sealed pans were allowed to stand overnight at room temperature before DSC analysis. An empty pan was used as a reference. The pans were heated from 30 to 120 C at a scanning rate of 10 C/min. The transition temperatures reported were the onset (To), peak (Tp) and conclusion (Tc) of the gelatinization endotherm. DH represents the required energy for disrupting hydrogen bonds within the crystalline zones. Each test was performed in duplicates. The gelatinization temperature range (R) and peak height index (PHI) were determined according to Equations (1) and (2) described by Krueger's method (Krueger, Knutson, Inglett, & Walker, 1987).
R ¼ 2 Tp To PHI ¼ DH
Tp To
(1)
(2)
2.10. Pasting properties of starch The pasting profiles of starches were recorded using a Rapid Visco Analyser (Perten Instruments Ltd., Australia). Starch slurries containing 9% w/w starch (dry weight) in a total weight of 28 g were prepared in the aluminium canisters. Starch slurries were held at 50 C for 1 min before heating at a rate of 12 C/min to 95 C, holding at 95 C for 3 min, and then cooling at a rate of 12 C/min to 50 C and held at 50 C for 2 min. The speed of the mixing paddle was 960 rpm for the first 10 s, then 160 rpm for the remainder of Fig. 1. SEM images of various chestnut starches (2000): A: Banhong; B: Yanlong; C: Yankui; D: Zaofeng.
C. Liu et al. / Food Hydrocolloids 43 (2015) 568e576
571
37 C with magnetic stirring. Aliquots (0.1 ml) were taken at intervals and mixed with 0.9 ml of 95% ethanol. The amount of released glucose was measured by a glucose oxidase/peroxidase (GOPOD) kit (Megazyme, K-GLUC). Starch classifications based on the rate of hydrolysis were: rapidly digested starch (RDS, digested within 20 min), slowly digested starch (SDS, digested between 20 and 120 min) and resistant starch (RS, undigested starch after 120 min). 2.13. Statistical analysis All analyses were replicated at least twice and mean and standard deviation values are reported. One-way analysis of variance (ANOVA) test was applied to compare all the data among the four varieties and to analyze the correlation between structure and functionality using SPSS Version 10.0 statistical software program (SPSS Inc., Chicago, Illinois, USA).
Fig. 2. X-ray diffractograms of four chestnut starches. A: Banhong; B: Yanlong; C: Yankui; D: Zaofeng.
3. Results and discussion 3.1. Composition of chestnuts and isolated starches
the experiment. Parameters recorded were pasting temperature (PT), peak viscosity (PV), trough viscosity (TV), final viscosity (FV), breakdown viscosity (BD, which is PV minus TV) and setback viscosity (SB, which is FV minus TV). 2.11. Textural analysis Measurement of force in compression was performed according to the method of Wang, Yin, Zhang, Xie, and Sun (2008). The texture of starch gels was determined in a TMS-PRO Stable Micro Systems texture analyzer (Food Technology Corporation, Virginia, USA) with a P/0.5R cylinder probe and 300 N load cell at room temperature (25 C). A standard two-cycle program was used to compress the gels for a 65% strain at 30 mm/min test speed, 60 mm/min pre-test speed, 120 mm/min post-test speed, 2 s pause time and 0.1 N trigger force. Texture parameters of hardness, adhesiveness, cohesiveness, springiness, gumminess and chewiness of gels were derived from the curves by the instrument software. 2.12. In vitro starch digestibility In vitro starch digestion was determined according to the method of Wang et al. (2011), which was modified from Englyst, Kingman, and Cummings (1992). Amylase solution was prepared by suspending 1.3 g of porcine pancreatic a-amylase (28 U/mg, Sigma A3176) in 12 ml of water at 37 C with magnetic stirring for 10 min. The mixture was centrifuged (1500 g for 10 min) and 0.1 ml of amyloglucosidase (3260 U/ml, Megazyme) was added to 9 ml of the supernatant. 100 mg chestnut starch was dispersed in 4 ml of 0.1 M sodium acetate buffer (pH 5.2) and 1 ml of the prepared enzyme solution was added. The mixture was incubated at
The chemical composition of chestnuts and isolated starches are presented in Table 1 and Table 2, respectively. The total starch content of four chestnut varieties ranged from 42.4% for Yanlong to 53.8% for Zaofeng. Total protein content of the chestnuts varied from 7.7% for Yankui to 9.5% for Banhong. There were small differences between chestnuts in lipid content and ash content, ranging from 2.1 to 2.4% and from 1.9 to 2.3%, respectively. These values were in the ranges reported in other studies (Borges et al., 2008; Miguelez et al., 2004). Isolated chestnut starches contained 0.1e0.2% of protein, 0.07e0.14% of ash and 0.62e0.79% of lipids (Table 2). The amylose content of four chestnut starches ranged from 21.2 to 22.3%, with no statistically significant differences being noted. Our results were consistent with the report by Demiate, Oetterer, and Wosiacki (2001). In other studies, the amylose content of chestnut starch was reported to be lower (Zhang et al., 2011) or higher (Correia, Cruz-Lopes, 2012; Yoo et al., 2012) than that of our starches. These differences can be attributed to the different geographical origin of the chestnuts, the different methods used for starch isolation, or the different methods used for amylose quantification. The damaged starch content of four chestnut starches was in the range of 2.2e4.9%, indicating the small damage to starch granules caused by the isolation method. In previous studies (Correia, Cruz~o-da-Costa, 2012), the alkaline and Lopes, 2012; Correia & Beira enzymatic methods for chestnut starch isolation were shown to result in high amount of damaged starch (>40%). 3.2. Granular morphology of chestnut starches The starch granules exhibited a variety of shapes, varying from round, croissant-like, irregular to triangular (Fig. 1). The surface of
Table 3 Swelling power of chestnut starches in distilled water. Varieties
Temperature ( C)
Banhong Yanlong Yankui Zaofeng
2.40 2.44 2.25 2.26
50
60 ± ± ± ±
0.05a 0.10a 0.03a 0.02a
5.21 5.19 4.78 4.57
70 ± ± ± ±
0.10a 0.05a 0.09b 0.08c
8.35 7.99 7.59 7.37
80 ± ± ± ±
0.05a 0.23a 0.25b 0.16b
Values are means ± SD. Means with the same letters in a column do not differ significantly (p < 0.05).
13.11 12.12 12.34 12.26
92.5 ± ± ± ±
0.93a 0.22a 0.26a 0.56a
19.04 18.91 18.45 16.28
± ± ± ±
0.15a 0.50a 0.76a 0.3 b
572
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Table 4 Thermal properties of the four starches from different chestnut varieties. Varieties
To ( C)
Banhong Yanlong Yankui Zaofeng
59.6 59.5 61.2 60.5
± ± ± ±
Tp ( C) 0.3c 0.2c 0.1a 0.5b
64.2 63.7 64.9 65.3
± ± ± ±
DH (J/g)
Tc ( C) 0.1c 0.2d 0.1b 0.1a
68.9 68.5 69.2 70.6
± ± ± ±
0.2b 0.1c 0.1b 0.3a
10.8 10.2 9.9 9.7
± ± ± ±
0.6a 0.4a 0.4a 0.5a
R ( C) 9.3 8.4 7.4 9.7
± ± ± ±
PHI (J/g C) 0.3a 0.0b 0.1c 0.7a
2.3 2.4 2.6 2.0
± ± ± ±
0.2a 0.1a 0.1a 0.0b
Values are means ± SD. Means with the same letters in a column do not differ significantly (p < 0.05).
starch granules appeared to be smooth and showed no evidence of ruptures, pores and channels. Four chestnut starch granules contained both populations of large and small granules. Some of the larger-sized starch granules had deep grooves (inset in Figs. 1A, B and D), and some were found to be fragmented (inset in Fig. 1C). Our results on the granular morphology of four Chinese chestnut starches were quite different from those reported previously, in which high amount of small irregularly-shape granules were shown (Correia, Cruz-Lopes, 2012; Cruz et al., 2013; Yoo et al., 2012). The granule size of chestnut starches varied greatly from about 1 to 16 mm as seen from SEM photographs. Similar results were also reported for other chestnut starches (Correia, Cruz-Lopes, 2012; Cruz et al., 2013; Yoo et al., 2012; Zhang et al., 2011). Yanlong starch was observed to contain less large-sized granules, whereas Zaofeng seemed to have more large-sized granules. The SEM observation was in general agreement the results of average particle size of starch granules, which followed the order of Yanlong (10.76 mm) < Banhong (12.52 mm) z Yankui (12.68 mm) < Zaofeng (18.10 mm) (Table 2). The range of particle size was from 0.8 to 51.5 mm (data not shown).
3.3. Starch crystallinity The X-ray diffraction patterns of chestnut starches are presented in Fig. 2. The X-ray diffraction patterns of chestnut starches were characterized by peaks at 15.4 , 17.0 , 20.0 and 23.0 2q. The X-ray diffraction profiles showed a strong peak at 23.0 2q and a weak shoulder peak at 17.0 2q (typical of A-type diffraction peaks), and a weak singlet at 5.6 2q (characteristic of B-type polymorphs), indicating that the chestnut starches were C-type crystalline starch. Our observation was in agreement with the other reports (Correia, Cruz-Lopes, 2012; Cruz et al., 2013; Yang et al., 2010; Yoo et al., 2012). The crystalline polymorph of chestnut starch was shown to vary with water content. At low water content, native chestnut starch presented a typical C-type X-ray diffraction pattern, which transformed into a B-type X-ray diffraction pattern as the water content increased (Cruz et al., 2013). The diffraction peak at 20.0 2q suggested the occurrence of crystalline amyloseelipid complexes in the granules. The relative crystallinity of Banhong starch, Yanlong, Yankui and Zaofeng starch was 28.5, 27.7, 26.3 and 29.0%, respectively.
3.4. Swelling power Swelling power of four chestnut starches was measured at several temperatures in the range 50e92.5 C (Table 3). The swelling power increased with increasing temperature from 50 to 92.5 C. The maximum swelling power of chestnut starch was observed at 92.5 C. At 50 C, which is below the onset gelatinization temperature of four chestnut starches, swelling power was similar. At 60 C, Banhong and Yanlong had higher swelling power than Yankui and Zaofeng. Swelling power at 92.5 C ranged from about 16.28 (Banhong) to 19.04 g/g (Zaofeng). These values were close to that observed for chestnut starch from var. Longal (Cruz et al., 2013). The swelling power of native starch granules is primarily a property of amylopectin molecules, with amylose acting as a dilute (Tester & Morrison, 1990) or the inhibiting force of amylopectin swelling (Wang & Copeland, 2012c). As there were no significant differences in amylose content, the differences in swelling power could be attributed to the fine structure of amylopectin molecules.
3.5. Thermal properties Thermal transition parameters of native chestnut starches are shown in Table 4. Differences between the starches were noted in the DSC transition temperatures (To, Tp and Tc), the transition temperature range (R) and peak height index (PHI). Yanlong had the lowest To (59.5 C), Tp (63.7 C) and Tc (68.5 C), while Zaofeng had the highest Tp (65.4 C) and Tc (70.6 C). Although the enthalpy changes of thermal transitions were in the range from 9.7 (Zaofeng) to 10.8 J/g (Banhong), no statistically significant differences were observed between the starches. This observation was in agreement with the small differences in starch crystallinity. The enthalpy change of starch granules was proposed to reflect the quantity of starch crystallites/double helices (Cooke & Gidley, 1992). Yankui had the narrowest transition temperature range (R), while the
Table 5 Syneresis properties of chestnut gels influenced by repeated freeze-thaw cycles. Varieties
Syneresis (%)
Banhong Yanlong Yankui Zaofeng
0.1 0.0 0.2 0.0
1st cycle ± ± ± ±
0.1a 0.0a 0.1a 0.0a
2nd cycle 3.2 2.3 4.5 5.9
± ± ± ±
0.2c 0.1d 0.2b 0.3a
3rd cycle 4.1 3.1 5.4 6.5
± ± ± ±
0.2c 0.2d 0.3b 0.2a
4th cycle 5.9 4.0 6.7 7.3
± ± ± ±
0.3b 0.2c 0.3a 0.3a
5th cycle 6.5 4.6 8.3 7.8
± ± ± ±
0.2b 0.2c 0.4a 0.3a
Values are means ± SD. Means with the same letters in a column do not differ significantly (p < 0.05).
Fig. 3. RVA pasting profiles of four chestnut starches.
C. Liu et al. / Food Hydrocolloids 43 (2015) 568e576
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Table 6 Pasting characteristics of starches from chestnut varieties. Varieties
Peak viscosity (cP)
Banhong Yanlong Yankui Zaofeng
2658 3301 3115 2803
± ± ± ±
43.8d 38.9a 21.9b 21.2c
Trough viscosity (cP) 2117 2376 2434 2086
± ± ± ±
76.4b 2.8a 19.8a 10.6b
Breakdown viscosity (cP) 541 925 681 718
± ± ± ±
32.5c 36.1a 9.4b 10.6b
Final viscosity (cP) 3802 4328 4451 3855
± ± ± ±
14.1c 19.8b 18.4a 29.7c
Setback viscosity (cP) 1685 1952 2017 1770
± ± ± ±
90.5b 22.6a 29.7a 40.3b
Pasting temperature ( C) 69.4 69.4 70.2 70.6
± ± ± ±
0.1b 0.0b 0.1 ab 0.3a
Values are means ± SD. Means with the same letters in a column do not differ significantly (p < 0.05).
broadest range was observed for Zaofeng. These values were in agreement with early studies on chestnut starches from Castanea crenata (Yoo et al., 2012). 3.6. Syneresis of starch pastes The syneresis of starch gels from the four chestnut varieties is presented in Table 5. The syneresis was nearly zero for all the chestnut starches after one freeze-thaw cycle, consistent with the observation of no exudation of free water from the starch gels. The syneresis of starch gels increased with storage time. Yanlong showed the lowest degree of syneresis (4.6%), whereas the highest value was observed for Yankui (8.3%) after five freeze-thaw cycles. Our results were similar with the report of Correia, Nunes, and Beir~ ao-da-Costa (2012), but lower than the results of Demiate et al. (2001). As compared with native corn starch and pea starch, chestnut starch presented a lower syneresis (data not shown). The low syneresis or exudation of water from starch gel during freezethaw storage was indicative of the slow retrogradation of starch gel due to the strong interaction between dispersed amylose/amylopectin and water molecules. The low syneresis of four chestnut starches also indicated that the chestnut starch would form a stable elastic soft gel during storage. During storage of a freshly cooked starch paste, retrogradation/recrystallization of starch molecules would occur, the extent to which retrogradation occurs was largely dependent on the storage time. Short-term storage leads to retrogradation of mainly amylose, whereas recrystallization of amylopectin side chains was much slower (Wang & Copeland, 2013).
3.8. Textural characteristics The textural properties of native starch gels varied with chestnut varieties (Table 7). For four chestnut starches, the gel of Banhong was the hardest (hardness of 1.27 N, adhesiveness of 0.91 mJ and cohesiveness of 0.41). The gel of Zaofeng was the softest (hardness of 0.86 N, adhesiveness of 0.79 mJ and cohesiveness of 0.33). The native chestnut starch gels showed the higher textural values as compared to native corn starch (data not shown). Starches that form the harder gels tend to have higher amylose content and longer amylopectin chains (Mua & Jackson, 1997). As there were slight differences in amylose content of four chestnut starches (Table 2), the significant differences in gel textural characteristics was then attributed to the length of amylopectin chains. 3.9. In vitro digestion properties The extent of hydrolysis of the chestnut starches by porcine pancreatic a-amylase and amyloglucosidase at different time intervals is shown in Fig. 4. Yankui had higher rapidly digestible starch (13.8%), lower resistant (77.6%) and slowly digestible starches (8.6%) compared to other starches. Banhong starch had approximately 17% higher RS content compared to Zaofeng starch (Table 8). Starch from Zaofeng variety was hydrolyzed to a greater extent (38% after 3 h) than others, whereas Banhong starch displayed the lowest extent of hydrolysis after 3 h (20%). In comparison with the chestnut starch reported by Pizzoferrato, Rotilio, and Pai (1999), the chestnut starches in the present study had lower amount of RDS and higher amount of RS.
3.7. Pasting properties 3.10. Correlation between properties of chestnut starches The overall shape of the RVA pasting curves was similar for the four starches (Fig. 3). However, significant differences were observed in pasting parameters (Table 6). Banhong starch showed the lowest pasting viscosities. The peak, trough and breakdown viscosities of Yanlong were higher than those of the other three starches, but the final and setback viscosities were lower than those of Yankui. The pasting temperatures of Banhong and Yanlong starches were the lowest (69.4 C), whereas Zaofeng starch had the highest pasting temperature (70.6 C). The pasting temperatures of starches were similar to the results of Demiate et al. (2001), but higher than the results of Correia, Nunes (2012), Zhang et al. (2011) and Cruz et al. (2013). The pasting viscosities of chestnut starches differed from those of early studies (Correia, Nunes, 2012; Yoo et al., 2012; Zhang et al., 2011). In addition to the granular structure, the differences in pasting viscosities could also be due to the different RVA analysis methods.
Native chestnut starch granules isolated from four varieties were characterized in this study. Average particle diameter of four starch granules was significantly negatively correlated with swelling power at 92.5 C (r ¼ 0.956, p < 0.05) (Table 9). The negative correlation indicates that small granules can absorb and hold more water within swollen starch molecules upon heating and cooling. Smaller granules in waxy and normal barley starches (Tang, Mitsunaga, & Kawamura, 2004), in potato and sweet potato starches (Chen, Schols & Voragen, 2003), and in wheat starches (Salman et al., 2009) were observed to have higher swelling power than larger granules. Greater hydration and swelling of smallgranule starches may be attributed to the higher specific surface areas. Small granules can absorb more water in comparison with large granules, which facilitated a more effective interaction berez-Pachecoa et al., 2014). tween granules and water molecules (Pe
Table 7 Textural characteristics of starches from chestnut varieties. Varieties
Hardness (N)
Banhong Yanlong Yankui Zaofeng
1.27 0.97 1.12 0.86
± ± ± ±
0.21a 0.13b 0.13 ab 0.10b
Adhesiveness (mJ) 0.91 0.69 1.08 0.79
± ± ± ±
0.05 ab 0.16b 0.03a 0.17b
Cohesiveness 0.41 0.31 0.41 0.33
± ± ± ±
0.04a 0.11a 0.03a 0.01a
Springiness (mm) 9.15 7.64 7.68 9.10
Values are means ± SD. Means with the same letters in a column do not differ significantly (p < 0.05).
± ± ± ±
0.60a 0.43b 0.31b 0.59a
Gumminess (N) 0.52 0.30 0.46 0.29
± ± ± ±
0.05a 0.09b 0.03a 0.03b
Chewiness (mJ) 4.69 2.22 3.52 2.61
± ± ± ±
0.75a 0.57c 0.25b 0.35c
0.6c 0.7b 0.4a 0.2b
5.5 10.4 8.6 20.9
RS ± ± ± ±
0.3d 0.5b 0.4c 0.6a
84.9 78.1 77.6 67.5
± ± ± ±
0.7a 0.5b 0.6b 0.5c
Values are means ± SD. Means with the same letters in a column do not differ significantly (p < 0.05).
1 0.591 1 0.028 0.745 1 0.793 0.584 0.223 1 0.064 0.006 0.213 0.213 1 0.987a 0.083 0.080 0.073 0.245 1 0.557 0.600 0.086 0.582 0.683 0.653 1 0.508 0.990b 0.955a 0.207 0.143 0.049 0.267 1 0.884 0.851 0.905 0.907 0.173 0.403 0.340 0.191 1 0.351 0.205 0.418 0.338 0.485 0.854 0.476 0.806 0.002 1 0.655 0.464 0.575 0.210 0.463 0.322 0.916 0.670 0.568 0.007 1 0.901 0.677 0.394 0.313 0.374 0.213 0.090 0.956a 0.919 0.331 0.424 1 0.802 0.495 0.700 0.073 0.296 0.198 0.374 0.457 0.777 0.884 0.146 0.711 1 0.428 0.819 0.973a 0.748 0.293 0.496 0.018 0.372 0.218 0.901 0.528 0.742 0.172 1 0.384 0.310 0.137 0.194 0.822 0.769 0.502 0.856 0.603 0.708 0.412 0.079 0.839 0.349
PV
DH Tc Tp To SP92.5 SP80 RC
AM, total amylose content; MPS, mean particle size; RC, relative crystallinity; SP80, swelling power at 80 C; SP92.5, swelling power at 92.5 C; To, onset temperature; Tp, peak temperature; Tc, conclusion temperature; DH, enthalpy of gelatinisation; PV, peak viscosity; TV, through viscosity; BD, breakdown viscosity; FV, final viscosity; SB, setback viscosity; PT, pasting temperature; SY, syneresis after five freeze-thaw cycles; HD, hardness; ADH, adhesiveness. a p < 0.05. b p < 0.01.
SDS ± ± ± ±
1 0.572 0.095 0.956a 0.367 0.841 0.988a 0.546 0.561 0.693 0.255 0.591 0.459 0.842 0.597 0.531 0.071
9.6 11.5 13.8 11.6
MPS
RDS
Banhong Yanlong Yankui Zaofeng
AM
Varieties
0.122 0.795 0.735 0.102 0.740 0.290 0.032 0.723 0.724 0.799 0.439 0.868 0.927 0.423 0.339 0.334 0.360
Table 8 Englyst digestion values of starch fractions of chestnut starches (excluding free glucose, g/100 g).
Table 9 Pearson correlation coefficients among various properties of different chestnut starches.
Average particle diameter of four starch granules was significantly positively correlated with DSC conclusion temperature Tc (r ¼ 0.988, p < 0.05) (Table 9). DSC thermal transition temperatures are thought to reflect the stability of starch crystallites, with higher stability crystallites showing higher transition temperatures. To has been postulated to represent the melting of the weakest crystallites, whereas Tc represents melting of crystallites of high stability (Jacobs, Eerlingen, Rouseu, Colonna, & Delcour, 1998). The positive correlation between average particle diameter and Tc suggests that crystallites in larger starch granules are more stable than those in smaller granules. Recently, the DSC thermal transition has been proposed to represent water absorption and swelling by starch granules, with the end point corresponding to the completion of these processes under the particular experimental conditions (Wang & Copeland, 2012b). In terms of this proposal, the positive correlation between average particle diameter and Tc suggests that larger starch granules tend to absorb water more slowly and complete the swelling behavior later than the smaller granules, thus leading to higher Tc. Swelling power at 92.5 C was significantly negatively correlated with DSC Tc (r ¼ 0.973, p < 0.05) and there were negative trends for To and Tp (Table 9). A negative correlation was also reported between swelling power and DSC parameters (Sandhu & Singh, 2007; Wang et al., 2011). This correlation indicates that starch granules with higher swelling power present lower Tc. Under the conditions in the DSC, starch granules absorb water and undergo only limited swelling (Wang & Copeland, 2012b; Wang & Copeland, 2013). At the same water/starch ratio, starch granules with higher swelling power were assumed to absorb water and complete the partial gelatinization in the DSC sooner than granules with lower swelling power. As expected, there was a significant positive correlation between pasting temperature and peak temperature in the DSC (r ¼ 0.956, p < 0.05). Analysis of correlations between the pasting parameters
TV
BD
Fig. 4. Kinetics of enzymatic hydrolysis of four chestnut starches.
1 0.253 0.459 0.550 0.056 0.444 0.172 0.619 0.908 0.121 0.892 0.852 0.058 0.217 0.288 0.646
FV
SB
PT
SY
HD
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MPS RC SP80 SP92.5 To Tp Tc DH PV TV BD FV SB PT SY HD ADH
574
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showed that trough viscosity had a positive correlation with final viscosity and setback viscosity, and that there was a positive correlation between final viscosity and setback viscosity (Table 9). There were no significant differences in amylose content of four chestnut starches. Analysis of variance indicated that amylose did not contribute significantly to the variability between starches in the other properties such as swelling power, thermal properties, syneresis, pasting characteristics, gel textural properties, and in vitro digestibility. Our results indicated that the amylopectin molecules, particularly the proportion and placement of A and B chains, are the main determinant of functionality and in vitro digestibility of native starch granules (Syahariza, Sar, Hasjim, Tizzotti, & Gilbert, 2013; Wang et al., 2011). In future, the detailed study of chain length distribution of amylopectin is necessary. 4. Conclusions Native Chinese chestnut starches isolated in this work presented significantly different physico-chemical and functional properties. The starch isolation method that was used in the present study allows producing pure starch with low amount of damaged starch. Four chestnut starches with no significant differences in amylose content displayed variability in swelling power, pasting characteristics, thermal and textural properties, freeze-thaw stability, and in susceptibility to in vitro attack by a-amylase. Correlation analysis indicated average particle diameter of starch granules plays an important role in determining the functional properties of starch granules. In addition, our results suggest that structural characteristics of amylopectin molecules, especially the length and placement of branches, are important determinants of the properties of native starch granules. As compared with corn starch reported in the study and previously (Cruz et al., 2013; Sandhu, Kaur, Singh, & Lim, 2008; Singh, Singh, Kaur, Singh Sodhi, & Singh Gill, 2003), native chestnut starch presented a higher swelling power, the lower pasting and gelatinization temperatures and a better freeze-thaw stability. These characteristics make native chestnut starch a potential technological alternative to corn starch, especially in the processing of starch products at low temperatures, in quality preservation of frozen starch-based products and other industrial applications. Acknowledgements This study was financially supported by the National Natural Science Foundation of China (31371720), the Natural Science Foundation of Tianjin (13JCYBJC38100), and Special National Forestry Public Welfare Industry Research (201304708). SW also greatly appreciates the financial support of Haihe River Scholar Program (000050401) from Tianjin University of Science & Technology. The authors would like to thank Research Centre of Modern Analytical Technique of Tianjin University of Science and Technology, and Analysis and Test Center of Hebei Normal University of Science and Technology for assistance with Scanning Electron Microscope, Particle Size Analyzer and XRD. Abbreviations used DSC PHI R RDS RS RVA SDS SEM
differential scanning calorimetry peak height index the transition temperature range rapidly digestible starch resistant starch rapid visco analyzer slowly digestible starch scanning electron microscope
To Tp Tc XRD
575
the onset peak conclusion X-ray powder diffraction.
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Food Hydrocolloids journal homepage: www.elsevier.com/locate/foodhyd
Structural and functional properties of starches from Chinese chestnuts Chang Liu a, b, 1, Shujun Wang a, *, 1, Xuedong Chang b, Shuo Wang a, * a b
Key Laboratory of Food Nutrition and Safety, Ministry of Education, Tianjin University of Science & Technology, Tianjin 300457, China College of Food Science and Technology, Hebei Normal University of Science and Technology, Qinhuangdao City 066600, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 23 December 2013 Accepted 14 July 2014 Available online 22 July 2014
Structural and functional properties of starches isolated from four varieties of chestnuts grown in China were characterized in this study. The starch granules exhibited a variety of shapes, varying from round, croissant-like, irregular to triangular. The amylose content of four chestnut starches was about 21e22%. Average particle diameter of the four starches varied between 10.8 and 18.1 mm. The X-ray patterns of four chestnut starches were of C-type, with relative crystallinity ranging between 26 and 29%. Although there were only small differences between the starches in amylose content, they displayed significant variability in physicochemical and functional properties, such as swelling power, pasting characteristics, thermal and textural properties, freeze-thaw stability, and in susceptibility to in vitro attack by enzymes. Average particle diameter of four starch granules was negatively correlated with swelling power at 92.5 C (r ¼ 0.956, p < 0.05), and positively correlated with conclusion temperature in the DSC (r ¼ 0.988, p < 0.05). Correlation between swelling power at 92.5 C and conclusion temperature was also significant (r ¼ 0.973, p < 0.05). This study provides sufficient information on properties of Chinese chestnut starches, which would be very helpful for their application in food and other industries. © 2014 Elsevier Ltd. All rights reserved.
Keywords: Chestnut Starch Morphology Amylose Functional properties
1. Introduction The chestnut (Castanea mollissima Bl.), belonging to the Fagaceae family, is one of the major nuts in China. It has a growing history of over 2000 years in China and makes great contribution to the national economy. The chestnut fruit is considered a high nutritional value food and has long been used as one of the Traditional Chinese Medicines for health care in China (Zhang, Chen, & Zhang, 2011). Chestnut fruit is also an important and popular food, which is consumed widely throughout Europe, America, and Asia (De Vasconcelos, Bennett, Rosa, & FerreiraCardoso, 2010). As one of the oldest edible fruits in northern hemisphere, chestnut was consumed as extensively as potato in the past (Ferreira-Cardoso, Sequeira, Torres-Pereira, Rodrigues, & Gomes, 1999). Although chestnuts are mainly consumed freshly after roasting, boiling or stir-frying with syrup, some processed chestnut products need to be reheated before eating. There is increasing evidence showing that the consumption of chestnuts has become more and more important for human nutrition due to * Corresponding authors. E-mail addresses: [email protected] (S. Wang), [email protected] (S. Wang). 1 Equal contribution. http://dx.doi.org/10.1016/j.foodhyd.2014.07.014 0268-005X/© 2014 Elsevier Ltd. All rights reserved.
the health benefits provided by the presence of bioactive components, including lectin, cysteine proteinase inhibitor and quercetin (Blomhoff, Carlsen, Andersen, & Jacobs, 2006). The chemical composition of chestnuts boasts the highest content in polymeric carbohydrates, considerable levels of vitamins, fibres, and acceptable content in lipids and adequate minerals (Borges, Carvalho, rdez, & Queijeiro, 2004). Correia, & Silva, 2007; Miguelez, Berna Recently, chestnut has received much more attention, as can be seen from the increasing publications. On one hand, chestnut presents a large potential for commercial use since it is a good source of starch. On the other hand, the consumption of chestnut has been shown to have many nutritional benefits. Starch is the main storage carbohydrate of higher plants and the main source of energy in human diets. It is also a cheap raw material with distinct physiochemical properties that are very important for its application in food and non-food industries. Native starch is highly variable between and within plant species. This variability is evident in granular structure and functional properties (Wang, Sharp, & Copeland, 2011). The functional properties of starch granules include swelling power, starch solubility, gelatinization, retrogradation, syneresis, and rheological behaviour, which are generally determined by the multiple characteristics of starch structure.
C. Liu et al. / Food Hydrocolloids 43 (2015) 568e576
500 ml of 0.15% NaOH and settled for 2 h at 4 C. The supernatant was decanted, the sedimented starch was resuspended in 500 ml of deionized water, and the pH was adjusted to 6.5 with 0.1 M HCl. The starch suspension was allowed to sediment and the supernatant was discarded. The sedimented starch was washed several times with distilled water until the densely deposited white starch was obtained, and then freeze dried in a Freeze Dryer (LGJ-10 freeze drier, Four-Ring Science Instrument Plant Beijing Co. Lts, Beijing, China) at 50 C.
Table 1 Chemical composition of chestnut fruits. Varieties
Total starch content (%)a
Banhong Yanlong Yankui Zaofeng
44.8 42.4 50.8 53.8
± ± ± ±
0.8b 1.0b 1.7a 1.6a
Protein (%)a 9.5 8.9 7.7 8.5
± ± ± ±
0.3a 0.4 ab 0.3c 0.2bc
Lipid (%)a 2.1 2.3 2.3 2.4
± ± ± ±
0.1a 0.2a 0.1a 0.2a
Ash (%)a 1.9 2.0 2.2 2.3
± ± ± ±
569
0.1a 0.2a 0.2a 0.1a
Values are means ± SD. Means with the same letters in a column do not differ significantly (p < 0.05). a Dry weight basis.
2.3. Determination of the chemical composition of chestnuts and isolated starches
Starch is the main constituent of chestnut fruit. The starch content in chestnut fruit ranges from 38 to 80% (Borges, Gonçalves, Carvalho, Correia, & Silva, 2008; Miguelez et al., 2004). Although the structural and functional properties of chestnut starches have ~o-da-Costa, 2010; Correia, Cruz-Lopes, been studied (Correia & Beira ~o-da-Costa, 2012; Cruz, Abraa ~o, Lemos, & Nunes, 2013; & Beira Yang, Jiang, Prasad, Gu, & Jiang, 2010; Yoo, Lee, Kim, & Shin, 2012; Zhang et al., 2011), there have been few comparative studies on the properties of starches from Chinese chestnut varieties. To extend the application of chestnut, the knowledge on the functional properties of chestnut starch, including its susceptibility to the enzymatic digestion, is extremely important. As a result, one aim of the present study was to characterize the structural and functional properties of starches from four Chinese chestnut varieties and to analyze the relationships between these properties. Another important aim was to compare the functional properties of chestnut starches and commonly used corn starches for the potential utilization of chestnut starch in food and other industries.
Total and damaged starch content were determined using Megazyme Total Starch and Starch Damage Assay Kits (Megazyme International Ireland Ltd. Bray Co., Wicklow, Ireland), respectively. The analyses were performed according to the instructions supplied with the kits. Amylose content was determined by iodine binding method according to Williams, Kuzina, and Hlynka (1970). Nitrogen, lipid and ash content were determined according to AOAC official procedures (methods 954.01, 920.39 and 923.03) (AOAC, 1997). Protein content was obtained by multiplying the nitrogen content by 6.25. Moisture content was determined by oven drying of the starch at 105 C until constant weight (925.40 AOAC method) (AOAC, 2000). 2.4. Morphology of starch Chestnut starch was imaged using the SU-1510 Scanning Electron Microscope (Hitachi Company, Japan). Starch samples were mounted on a specimen holder using a double-sided carbon adhesive tape and sputter-coated with gold. An accelerating voltage of 5 kV was used during scanning.
2. Materials and methods 2.1. Samples Four Chinese chestnut varieties (Banhong, Zaofeng, Yanlong, Yankui) were obtained from chestnut storage and processing center of Hebei province, China. Yanlong is an advanced line from the breeding program of Hebei Normal University of Science and Technology. It was identified by Committee of Forestry Varieties of Hebei Province in 2009, and had Plant Breeders' Rights Application Number (S-SV-CM-003-2009). The chestnuts were grown and harvested at Yanshan Mountain in 2012 season. The harvested fruits were collected and stored at 4 C.
2.5. Particle size distribution
2.2. Starch extraction
X-ray diffraction analysis was performed using a D/max2500vk/pc X-ray diffractometer (Rigaku Corporation, Tokyo, Japan) operating at 40 V and 30 mA. Starches were equilibrated over a saturated potassium chloride (KCl) solution at room temperature for one week before analysis (Wang, Yu, Zhu, Yu, & Jin, 2009). The intensity was measured from 3 to 40 as a function of 2q and at a scanning speed of 1 /min and a step size of 0.02 . The degree of crystallinity was determined quantitatively following the n, & An ~o n, 2004). method reported previously (Ribotta, Cuffini, Leo The crystallinity of starch was calculated as a ratio of the crystalline
Particle size distribution of starch granules was measured using Laser Diffraction Particle Size Analyzer LA-920 (Horiba Instruments Ltd., Japan) according to the instructions supplied with the instrument. The starch was evenly dispersed in ethanol with magnetic agitation to attain a transmittance of 80%. 2.6. X-ray diffraction
Starch was isolated according to the method of Wang et al. (2011) with modifications as follows. The chestnuts (700 g) were rinsed, peeled and homogenized in a kitchen blender with 1.5 L distilled water for 1e2 min at maximum speed. The starch slurry was passed through a 140 mesh filtrating cloth. The resulting starch suspension was allowed to settle overnight at 4 C. The supernatant was decanted, and the brownish grey layer on top of the white starch sediment was removed. The starch pellet was dispersed in
Table 2 Chemical composition of chestnut starches. Varieties
Moisture (%)
Banhong Yanlong Yankui Zaofeng
5.52 5.23 5.70 5.93
± ± ± ±
0.24a 0.36a 0.11a 0.3 a
Protein (%)a 0.20 0.10 0.13 0.15
± ± ± ±
0.04a 0.03a 0.05a 0.06a
Lipid (%)a 0.79 0.62 0.73 0.65
± ± ± ±
0.08a 0.04a 0.06a 0.05a
Ash (%)a 0.07 0.10 0.14 0.09
± ± ± ±
0.02a 0.03a 0.05a 0.02a
Amylose (%) 21.16 21.80 22.27 21.67
Values are means ± SD. Means with the same letters in a column do not differ significantly (p < 0.05). a Dry weight basis.
± ± ± ±
0.38a 0.18a 0.25a 0.15a
Damage starch (%) 3.63 4.94 3.25 2.22
± ± ± ±
0.21b 0.28a 0.25c 0.10d
Mean particle size (mm) 12.68 10.76 12.52 18.10
± ± ± ±
0.05b 0.03c 0.06b 0.25a
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area to the total area using the JADE 5.0 software (Materials Data Inc, Livermore, CA, USA). 2.7. Swelling power Starch swelling power was determined in excess water at temperatures from 50 to 92.5 C according to the method of Konik-Rose et al. (2001) with some modifications (Wang & Copeland, 2012a). The water/starch ratio used in the swelling power test was 25:1, namely 1 mL water/40 mg starch. Starch swelling power was calculated as the ratio of the weight of the swollen starch to the initial dry weight of starch. 2.8. Syneresis The starch suspension (6%, w/v, dry weight basis) was heated for 30 min in a boiling water bath with constant stirring, and then the starch paste was transferred into a mould and cooled to 20 C. The syneresis of starch gels were measured at room temperature respectively. The other moulds were frozen in a chest freezer at 20 C for 22 h and then thawed at 30 C in a water bath for 2 h to reach an equilibration. Syneresis was measured as % amount of water released after centrifugation at 986 g for 20 min. The freezethaw cycle was repeated for up to 5 times to compare the freezethaw stability of chestnut starch gels. 2.9. Thermal properties Thermal properties of starches were studied using a differential scanning calorimeter (200 F3, Netzsch, Germany) equipped with a thermal analysis data station. The operating conditions of thermal transition were described elsewhere (Wang & Copeland, 2012b). Briefly, about 3 mg of starch were weighed into a 40 mL aluminium DSC crucibles, Distilled water was added to the starch in the DSC pans with a microsyringe to obtain a water:starch ration of 2:1 (w/ w). The sealed pans were allowed to stand overnight at room temperature before DSC analysis. An empty pan was used as a reference. The pans were heated from 30 to 120 C at a scanning rate of 10 C/min. The transition temperatures reported were the onset (To), peak (Tp) and conclusion (Tc) of the gelatinization endotherm. DH represents the required energy for disrupting hydrogen bonds within the crystalline zones. Each test was performed in duplicates. The gelatinization temperature range (R) and peak height index (PHI) were determined according to Equations (1) and (2) described by Krueger's method (Krueger, Knutson, Inglett, & Walker, 1987).
R ¼ 2 Tp To PHI ¼ DH
Tp To
(1)
(2)
2.10. Pasting properties of starch The pasting profiles of starches were recorded using a Rapid Visco Analyser (Perten Instruments Ltd., Australia). Starch slurries containing 9% w/w starch (dry weight) in a total weight of 28 g were prepared in the aluminium canisters. Starch slurries were held at 50 C for 1 min before heating at a rate of 12 C/min to 95 C, holding at 95 C for 3 min, and then cooling at a rate of 12 C/min to 50 C and held at 50 C for 2 min. The speed of the mixing paddle was 960 rpm for the first 10 s, then 160 rpm for the remainder of Fig. 1. SEM images of various chestnut starches (2000): A: Banhong; B: Yanlong; C: Yankui; D: Zaofeng.
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37 C with magnetic stirring. Aliquots (0.1 ml) were taken at intervals and mixed with 0.9 ml of 95% ethanol. The amount of released glucose was measured by a glucose oxidase/peroxidase (GOPOD) kit (Megazyme, K-GLUC). Starch classifications based on the rate of hydrolysis were: rapidly digested starch (RDS, digested within 20 min), slowly digested starch (SDS, digested between 20 and 120 min) and resistant starch (RS, undigested starch after 120 min). 2.13. Statistical analysis All analyses were replicated at least twice and mean and standard deviation values are reported. One-way analysis of variance (ANOVA) test was applied to compare all the data among the four varieties and to analyze the correlation between structure and functionality using SPSS Version 10.0 statistical software program (SPSS Inc., Chicago, Illinois, USA).
Fig. 2. X-ray diffractograms of four chestnut starches. A: Banhong; B: Yanlong; C: Yankui; D: Zaofeng.
3. Results and discussion 3.1. Composition of chestnuts and isolated starches
the experiment. Parameters recorded were pasting temperature (PT), peak viscosity (PV), trough viscosity (TV), final viscosity (FV), breakdown viscosity (BD, which is PV minus TV) and setback viscosity (SB, which is FV minus TV). 2.11. Textural analysis Measurement of force in compression was performed according to the method of Wang, Yin, Zhang, Xie, and Sun (2008). The texture of starch gels was determined in a TMS-PRO Stable Micro Systems texture analyzer (Food Technology Corporation, Virginia, USA) with a P/0.5R cylinder probe and 300 N load cell at room temperature (25 C). A standard two-cycle program was used to compress the gels for a 65% strain at 30 mm/min test speed, 60 mm/min pre-test speed, 120 mm/min post-test speed, 2 s pause time and 0.1 N trigger force. Texture parameters of hardness, adhesiveness, cohesiveness, springiness, gumminess and chewiness of gels were derived from the curves by the instrument software. 2.12. In vitro starch digestibility In vitro starch digestion was determined according to the method of Wang et al. (2011), which was modified from Englyst, Kingman, and Cummings (1992). Amylase solution was prepared by suspending 1.3 g of porcine pancreatic a-amylase (28 U/mg, Sigma A3176) in 12 ml of water at 37 C with magnetic stirring for 10 min. The mixture was centrifuged (1500 g for 10 min) and 0.1 ml of amyloglucosidase (3260 U/ml, Megazyme) was added to 9 ml of the supernatant. 100 mg chestnut starch was dispersed in 4 ml of 0.1 M sodium acetate buffer (pH 5.2) and 1 ml of the prepared enzyme solution was added. The mixture was incubated at
The chemical composition of chestnuts and isolated starches are presented in Table 1 and Table 2, respectively. The total starch content of four chestnut varieties ranged from 42.4% for Yanlong to 53.8% for Zaofeng. Total protein content of the chestnuts varied from 7.7% for Yankui to 9.5% for Banhong. There were small differences between chestnuts in lipid content and ash content, ranging from 2.1 to 2.4% and from 1.9 to 2.3%, respectively. These values were in the ranges reported in other studies (Borges et al., 2008; Miguelez et al., 2004). Isolated chestnut starches contained 0.1e0.2% of protein, 0.07e0.14% of ash and 0.62e0.79% of lipids (Table 2). The amylose content of four chestnut starches ranged from 21.2 to 22.3%, with no statistically significant differences being noted. Our results were consistent with the report by Demiate, Oetterer, and Wosiacki (2001). In other studies, the amylose content of chestnut starch was reported to be lower (Zhang et al., 2011) or higher (Correia, Cruz-Lopes, 2012; Yoo et al., 2012) than that of our starches. These differences can be attributed to the different geographical origin of the chestnuts, the different methods used for starch isolation, or the different methods used for amylose quantification. The damaged starch content of four chestnut starches was in the range of 2.2e4.9%, indicating the small damage to starch granules caused by the isolation method. In previous studies (Correia, Cruz~o-da-Costa, 2012), the alkaline and Lopes, 2012; Correia & Beira enzymatic methods for chestnut starch isolation were shown to result in high amount of damaged starch (>40%). 3.2. Granular morphology of chestnut starches The starch granules exhibited a variety of shapes, varying from round, croissant-like, irregular to triangular (Fig. 1). The surface of
Table 3 Swelling power of chestnut starches in distilled water. Varieties
Temperature ( C)
Banhong Yanlong Yankui Zaofeng
2.40 2.44 2.25 2.26
50
60 ± ± ± ±
0.05a 0.10a 0.03a 0.02a
5.21 5.19 4.78 4.57
70 ± ± ± ±
0.10a 0.05a 0.09b 0.08c
8.35 7.99 7.59 7.37
80 ± ± ± ±
0.05a 0.23a 0.25b 0.16b
Values are means ± SD. Means with the same letters in a column do not differ significantly (p < 0.05).
13.11 12.12 12.34 12.26
92.5 ± ± ± ±
0.93a 0.22a 0.26a 0.56a
19.04 18.91 18.45 16.28
± ± ± ±
0.15a 0.50a 0.76a 0.3 b
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Table 4 Thermal properties of the four starches from different chestnut varieties. Varieties
To ( C)
Banhong Yanlong Yankui Zaofeng
59.6 59.5 61.2 60.5
± ± ± ±
Tp ( C) 0.3c 0.2c 0.1a 0.5b
64.2 63.7 64.9 65.3
± ± ± ±
DH (J/g)
Tc ( C) 0.1c 0.2d 0.1b 0.1a
68.9 68.5 69.2 70.6
± ± ± ±
0.2b 0.1c 0.1b 0.3a
10.8 10.2 9.9 9.7
± ± ± ±
0.6a 0.4a 0.4a 0.5a
R ( C) 9.3 8.4 7.4 9.7
± ± ± ±
PHI (J/g C) 0.3a 0.0b 0.1c 0.7a
2.3 2.4 2.6 2.0
± ± ± ±
0.2a 0.1a 0.1a 0.0b
Values are means ± SD. Means with the same letters in a column do not differ significantly (p < 0.05).
starch granules appeared to be smooth and showed no evidence of ruptures, pores and channels. Four chestnut starch granules contained both populations of large and small granules. Some of the larger-sized starch granules had deep grooves (inset in Figs. 1A, B and D), and some were found to be fragmented (inset in Fig. 1C). Our results on the granular morphology of four Chinese chestnut starches were quite different from those reported previously, in which high amount of small irregularly-shape granules were shown (Correia, Cruz-Lopes, 2012; Cruz et al., 2013; Yoo et al., 2012). The granule size of chestnut starches varied greatly from about 1 to 16 mm as seen from SEM photographs. Similar results were also reported for other chestnut starches (Correia, Cruz-Lopes, 2012; Cruz et al., 2013; Yoo et al., 2012; Zhang et al., 2011). Yanlong starch was observed to contain less large-sized granules, whereas Zaofeng seemed to have more large-sized granules. The SEM observation was in general agreement the results of average particle size of starch granules, which followed the order of Yanlong (10.76 mm) < Banhong (12.52 mm) z Yankui (12.68 mm) < Zaofeng (18.10 mm) (Table 2). The range of particle size was from 0.8 to 51.5 mm (data not shown).
3.3. Starch crystallinity The X-ray diffraction patterns of chestnut starches are presented in Fig. 2. The X-ray diffraction patterns of chestnut starches were characterized by peaks at 15.4 , 17.0 , 20.0 and 23.0 2q. The X-ray diffraction profiles showed a strong peak at 23.0 2q and a weak shoulder peak at 17.0 2q (typical of A-type diffraction peaks), and a weak singlet at 5.6 2q (characteristic of B-type polymorphs), indicating that the chestnut starches were C-type crystalline starch. Our observation was in agreement with the other reports (Correia, Cruz-Lopes, 2012; Cruz et al., 2013; Yang et al., 2010; Yoo et al., 2012). The crystalline polymorph of chestnut starch was shown to vary with water content. At low water content, native chestnut starch presented a typical C-type X-ray diffraction pattern, which transformed into a B-type X-ray diffraction pattern as the water content increased (Cruz et al., 2013). The diffraction peak at 20.0 2q suggested the occurrence of crystalline amyloseelipid complexes in the granules. The relative crystallinity of Banhong starch, Yanlong, Yankui and Zaofeng starch was 28.5, 27.7, 26.3 and 29.0%, respectively.
3.4. Swelling power Swelling power of four chestnut starches was measured at several temperatures in the range 50e92.5 C (Table 3). The swelling power increased with increasing temperature from 50 to 92.5 C. The maximum swelling power of chestnut starch was observed at 92.5 C. At 50 C, which is below the onset gelatinization temperature of four chestnut starches, swelling power was similar. At 60 C, Banhong and Yanlong had higher swelling power than Yankui and Zaofeng. Swelling power at 92.5 C ranged from about 16.28 (Banhong) to 19.04 g/g (Zaofeng). These values were close to that observed for chestnut starch from var. Longal (Cruz et al., 2013). The swelling power of native starch granules is primarily a property of amylopectin molecules, with amylose acting as a dilute (Tester & Morrison, 1990) or the inhibiting force of amylopectin swelling (Wang & Copeland, 2012c). As there were no significant differences in amylose content, the differences in swelling power could be attributed to the fine structure of amylopectin molecules.
3.5. Thermal properties Thermal transition parameters of native chestnut starches are shown in Table 4. Differences between the starches were noted in the DSC transition temperatures (To, Tp and Tc), the transition temperature range (R) and peak height index (PHI). Yanlong had the lowest To (59.5 C), Tp (63.7 C) and Tc (68.5 C), while Zaofeng had the highest Tp (65.4 C) and Tc (70.6 C). Although the enthalpy changes of thermal transitions were in the range from 9.7 (Zaofeng) to 10.8 J/g (Banhong), no statistically significant differences were observed between the starches. This observation was in agreement with the small differences in starch crystallinity. The enthalpy change of starch granules was proposed to reflect the quantity of starch crystallites/double helices (Cooke & Gidley, 1992). Yankui had the narrowest transition temperature range (R), while the
Table 5 Syneresis properties of chestnut gels influenced by repeated freeze-thaw cycles. Varieties
Syneresis (%)
Banhong Yanlong Yankui Zaofeng
0.1 0.0 0.2 0.0
1st cycle ± ± ± ±
0.1a 0.0a 0.1a 0.0a
2nd cycle 3.2 2.3 4.5 5.9
± ± ± ±
0.2c 0.1d 0.2b 0.3a
3rd cycle 4.1 3.1 5.4 6.5
± ± ± ±
0.2c 0.2d 0.3b 0.2a
4th cycle 5.9 4.0 6.7 7.3
± ± ± ±
0.3b 0.2c 0.3a 0.3a
5th cycle 6.5 4.6 8.3 7.8
± ± ± ±
0.2b 0.2c 0.4a 0.3a
Values are means ± SD. Means with the same letters in a column do not differ significantly (p < 0.05).
Fig. 3. RVA pasting profiles of four chestnut starches.
C. Liu et al. / Food Hydrocolloids 43 (2015) 568e576
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Table 6 Pasting characteristics of starches from chestnut varieties. Varieties
Peak viscosity (cP)
Banhong Yanlong Yankui Zaofeng
2658 3301 3115 2803
± ± ± ±
43.8d 38.9a 21.9b 21.2c
Trough viscosity (cP) 2117 2376 2434 2086
± ± ± ±
76.4b 2.8a 19.8a 10.6b
Breakdown viscosity (cP) 541 925 681 718
± ± ± ±
32.5c 36.1a 9.4b 10.6b
Final viscosity (cP) 3802 4328 4451 3855
± ± ± ±
14.1c 19.8b 18.4a 29.7c
Setback viscosity (cP) 1685 1952 2017 1770
± ± ± ±
90.5b 22.6a 29.7a 40.3b
Pasting temperature ( C) 69.4 69.4 70.2 70.6
± ± ± ±
0.1b 0.0b 0.1 ab 0.3a
Values are means ± SD. Means with the same letters in a column do not differ significantly (p < 0.05).
broadest range was observed for Zaofeng. These values were in agreement with early studies on chestnut starches from Castanea crenata (Yoo et al., 2012). 3.6. Syneresis of starch pastes The syneresis of starch gels from the four chestnut varieties is presented in Table 5. The syneresis was nearly zero for all the chestnut starches after one freeze-thaw cycle, consistent with the observation of no exudation of free water from the starch gels. The syneresis of starch gels increased with storage time. Yanlong showed the lowest degree of syneresis (4.6%), whereas the highest value was observed for Yankui (8.3%) after five freeze-thaw cycles. Our results were similar with the report of Correia, Nunes, and Beir~ ao-da-Costa (2012), but lower than the results of Demiate et al. (2001). As compared with native corn starch and pea starch, chestnut starch presented a lower syneresis (data not shown). The low syneresis or exudation of water from starch gel during freezethaw storage was indicative of the slow retrogradation of starch gel due to the strong interaction between dispersed amylose/amylopectin and water molecules. The low syneresis of four chestnut starches also indicated that the chestnut starch would form a stable elastic soft gel during storage. During storage of a freshly cooked starch paste, retrogradation/recrystallization of starch molecules would occur, the extent to which retrogradation occurs was largely dependent on the storage time. Short-term storage leads to retrogradation of mainly amylose, whereas recrystallization of amylopectin side chains was much slower (Wang & Copeland, 2013).
3.8. Textural characteristics The textural properties of native starch gels varied with chestnut varieties (Table 7). For four chestnut starches, the gel of Banhong was the hardest (hardness of 1.27 N, adhesiveness of 0.91 mJ and cohesiveness of 0.41). The gel of Zaofeng was the softest (hardness of 0.86 N, adhesiveness of 0.79 mJ and cohesiveness of 0.33). The native chestnut starch gels showed the higher textural values as compared to native corn starch (data not shown). Starches that form the harder gels tend to have higher amylose content and longer amylopectin chains (Mua & Jackson, 1997). As there were slight differences in amylose content of four chestnut starches (Table 2), the significant differences in gel textural characteristics was then attributed to the length of amylopectin chains. 3.9. In vitro digestion properties The extent of hydrolysis of the chestnut starches by porcine pancreatic a-amylase and amyloglucosidase at different time intervals is shown in Fig. 4. Yankui had higher rapidly digestible starch (13.8%), lower resistant (77.6%) and slowly digestible starches (8.6%) compared to other starches. Banhong starch had approximately 17% higher RS content compared to Zaofeng starch (Table 8). Starch from Zaofeng variety was hydrolyzed to a greater extent (38% after 3 h) than others, whereas Banhong starch displayed the lowest extent of hydrolysis after 3 h (20%). In comparison with the chestnut starch reported by Pizzoferrato, Rotilio, and Pai (1999), the chestnut starches in the present study had lower amount of RDS and higher amount of RS.
3.7. Pasting properties 3.10. Correlation between properties of chestnut starches The overall shape of the RVA pasting curves was similar for the four starches (Fig. 3). However, significant differences were observed in pasting parameters (Table 6). Banhong starch showed the lowest pasting viscosities. The peak, trough and breakdown viscosities of Yanlong were higher than those of the other three starches, but the final and setback viscosities were lower than those of Yankui. The pasting temperatures of Banhong and Yanlong starches were the lowest (69.4 C), whereas Zaofeng starch had the highest pasting temperature (70.6 C). The pasting temperatures of starches were similar to the results of Demiate et al. (2001), but higher than the results of Correia, Nunes (2012), Zhang et al. (2011) and Cruz et al. (2013). The pasting viscosities of chestnut starches differed from those of early studies (Correia, Nunes, 2012; Yoo et al., 2012; Zhang et al., 2011). In addition to the granular structure, the differences in pasting viscosities could also be due to the different RVA analysis methods.
Native chestnut starch granules isolated from four varieties were characterized in this study. Average particle diameter of four starch granules was significantly negatively correlated with swelling power at 92.5 C (r ¼ 0.956, p < 0.05) (Table 9). The negative correlation indicates that small granules can absorb and hold more water within swollen starch molecules upon heating and cooling. Smaller granules in waxy and normal barley starches (Tang, Mitsunaga, & Kawamura, 2004), in potato and sweet potato starches (Chen, Schols & Voragen, 2003), and in wheat starches (Salman et al., 2009) were observed to have higher swelling power than larger granules. Greater hydration and swelling of smallgranule starches may be attributed to the higher specific surface areas. Small granules can absorb more water in comparison with large granules, which facilitated a more effective interaction berez-Pachecoa et al., 2014). tween granules and water molecules (Pe
Table 7 Textural characteristics of starches from chestnut varieties. Varieties
Hardness (N)
Banhong Yanlong Yankui Zaofeng
1.27 0.97 1.12 0.86
± ± ± ±
0.21a 0.13b 0.13 ab 0.10b
Adhesiveness (mJ) 0.91 0.69 1.08 0.79
± ± ± ±
0.05 ab 0.16b 0.03a 0.17b
Cohesiveness 0.41 0.31 0.41 0.33
± ± ± ±
0.04a 0.11a 0.03a 0.01a
Springiness (mm) 9.15 7.64 7.68 9.10
Values are means ± SD. Means with the same letters in a column do not differ significantly (p < 0.05).
± ± ± ±
0.60a 0.43b 0.31b 0.59a
Gumminess (N) 0.52 0.30 0.46 0.29
± ± ± ±
0.05a 0.09b 0.03a 0.03b
Chewiness (mJ) 4.69 2.22 3.52 2.61
± ± ± ±
0.75a 0.57c 0.25b 0.35c
0.6c 0.7b 0.4a 0.2b
5.5 10.4 8.6 20.9
RS ± ± ± ±
0.3d 0.5b 0.4c 0.6a
84.9 78.1 77.6 67.5
± ± ± ±
0.7a 0.5b 0.6b 0.5c
Values are means ± SD. Means with the same letters in a column do not differ significantly (p < 0.05).
1 0.591 1 0.028 0.745 1 0.793 0.584 0.223 1 0.064 0.006 0.213 0.213 1 0.987a 0.083 0.080 0.073 0.245 1 0.557 0.600 0.086 0.582 0.683 0.653 1 0.508 0.990b 0.955a 0.207 0.143 0.049 0.267 1 0.884 0.851 0.905 0.907 0.173 0.403 0.340 0.191 1 0.351 0.205 0.418 0.338 0.485 0.854 0.476 0.806 0.002 1 0.655 0.464 0.575 0.210 0.463 0.322 0.916 0.670 0.568 0.007 1 0.901 0.677 0.394 0.313 0.374 0.213 0.090 0.956a 0.919 0.331 0.424 1 0.802 0.495 0.700 0.073 0.296 0.198 0.374 0.457 0.777 0.884 0.146 0.711 1 0.428 0.819 0.973a 0.748 0.293 0.496 0.018 0.372 0.218 0.901 0.528 0.742 0.172 1 0.384 0.310 0.137 0.194 0.822 0.769 0.502 0.856 0.603 0.708 0.412 0.079 0.839 0.349
PV
DH Tc Tp To SP92.5 SP80 RC
AM, total amylose content; MPS, mean particle size; RC, relative crystallinity; SP80, swelling power at 80 C; SP92.5, swelling power at 92.5 C; To, onset temperature; Tp, peak temperature; Tc, conclusion temperature; DH, enthalpy of gelatinisation; PV, peak viscosity; TV, through viscosity; BD, breakdown viscosity; FV, final viscosity; SB, setback viscosity; PT, pasting temperature; SY, syneresis after five freeze-thaw cycles; HD, hardness; ADH, adhesiveness. a p < 0.05. b p < 0.01.
SDS ± ± ± ±
1 0.572 0.095 0.956a 0.367 0.841 0.988a 0.546 0.561 0.693 0.255 0.591 0.459 0.842 0.597 0.531 0.071
9.6 11.5 13.8 11.6
MPS
RDS
Banhong Yanlong Yankui Zaofeng
AM
Varieties
0.122 0.795 0.735 0.102 0.740 0.290 0.032 0.723 0.724 0.799 0.439 0.868 0.927 0.423 0.339 0.334 0.360
Table 8 Englyst digestion values of starch fractions of chestnut starches (excluding free glucose, g/100 g).
Table 9 Pearson correlation coefficients among various properties of different chestnut starches.
Average particle diameter of four starch granules was significantly positively correlated with DSC conclusion temperature Tc (r ¼ 0.988, p < 0.05) (Table 9). DSC thermal transition temperatures are thought to reflect the stability of starch crystallites, with higher stability crystallites showing higher transition temperatures. To has been postulated to represent the melting of the weakest crystallites, whereas Tc represents melting of crystallites of high stability (Jacobs, Eerlingen, Rouseu, Colonna, & Delcour, 1998). The positive correlation between average particle diameter and Tc suggests that crystallites in larger starch granules are more stable than those in smaller granules. Recently, the DSC thermal transition has been proposed to represent water absorption and swelling by starch granules, with the end point corresponding to the completion of these processes under the particular experimental conditions (Wang & Copeland, 2012b). In terms of this proposal, the positive correlation between average particle diameter and Tc suggests that larger starch granules tend to absorb water more slowly and complete the swelling behavior later than the smaller granules, thus leading to higher Tc. Swelling power at 92.5 C was significantly negatively correlated with DSC Tc (r ¼ 0.973, p < 0.05) and there were negative trends for To and Tp (Table 9). A negative correlation was also reported between swelling power and DSC parameters (Sandhu & Singh, 2007; Wang et al., 2011). This correlation indicates that starch granules with higher swelling power present lower Tc. Under the conditions in the DSC, starch granules absorb water and undergo only limited swelling (Wang & Copeland, 2012b; Wang & Copeland, 2013). At the same water/starch ratio, starch granules with higher swelling power were assumed to absorb water and complete the partial gelatinization in the DSC sooner than granules with lower swelling power. As expected, there was a significant positive correlation between pasting temperature and peak temperature in the DSC (r ¼ 0.956, p < 0.05). Analysis of correlations between the pasting parameters
TV
BD
Fig. 4. Kinetics of enzymatic hydrolysis of four chestnut starches.
1 0.253 0.459 0.550 0.056 0.444 0.172 0.619 0.908 0.121 0.892 0.852 0.058 0.217 0.288 0.646
FV
SB
PT
SY
HD
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MPS RC SP80 SP92.5 To Tp Tc DH PV TV BD FV SB PT SY HD ADH
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showed that trough viscosity had a positive correlation with final viscosity and setback viscosity, and that there was a positive correlation between final viscosity and setback viscosity (Table 9). There were no significant differences in amylose content of four chestnut starches. Analysis of variance indicated that amylose did not contribute significantly to the variability between starches in the other properties such as swelling power, thermal properties, syneresis, pasting characteristics, gel textural properties, and in vitro digestibility. Our results indicated that the amylopectin molecules, particularly the proportion and placement of A and B chains, are the main determinant of functionality and in vitro digestibility of native starch granules (Syahariza, Sar, Hasjim, Tizzotti, & Gilbert, 2013; Wang et al., 2011). In future, the detailed study of chain length distribution of amylopectin is necessary. 4. Conclusions Native Chinese chestnut starches isolated in this work presented significantly different physico-chemical and functional properties. The starch isolation method that was used in the present study allows producing pure starch with low amount of damaged starch. Four chestnut starches with no significant differences in amylose content displayed variability in swelling power, pasting characteristics, thermal and textural properties, freeze-thaw stability, and in susceptibility to in vitro attack by a-amylase. Correlation analysis indicated average particle diameter of starch granules plays an important role in determining the functional properties of starch granules. In addition, our results suggest that structural characteristics of amylopectin molecules, especially the length and placement of branches, are important determinants of the properties of native starch granules. As compared with corn starch reported in the study and previously (Cruz et al., 2013; Sandhu, Kaur, Singh, & Lim, 2008; Singh, Singh, Kaur, Singh Sodhi, & Singh Gill, 2003), native chestnut starch presented a higher swelling power, the lower pasting and gelatinization temperatures and a better freeze-thaw stability. These characteristics make native chestnut starch a potential technological alternative to corn starch, especially in the processing of starch products at low temperatures, in quality preservation of frozen starch-based products and other industrial applications. Acknowledgements This study was financially supported by the National Natural Science Foundation of China (31371720), the Natural Science Foundation of Tianjin (13JCYBJC38100), and Special National Forestry Public Welfare Industry Research (201304708). SW also greatly appreciates the financial support of Haihe River Scholar Program (000050401) from Tianjin University of Science & Technology. The authors would like to thank Research Centre of Modern Analytical Technique of Tianjin University of Science and Technology, and Analysis and Test Center of Hebei Normal University of Science and Technology for assistance with Scanning Electron Microscope, Particle Size Analyzer and XRD. Abbreviations used DSC PHI R RDS RS RVA SDS SEM
differential scanning calorimetry peak height index the transition temperature range rapidly digestible starch resistant starch rapid visco analyzer slowly digestible starch scanning electron microscope
To Tp Tc XRD
575
the onset peak conclusion X-ray powder diffraction.
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