Multiscale Structural Changes of Wheat and Yam Starches during

Subscriber access provided by GAZI UNIV

Article

Multi-scale structural changes of wheat and yam starches during cooking and their effect on in vitro enzymatic digestibility Shujun Wang, Shaokang Wang, Peng Guo, Lu Liu, and Shuo Wang J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.6b04272 • Publication Date (Web): 12 Dec 2016 Downloaded from http://pubs.acs.org on December 13, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Journal of Agricultural and Food Chemistry is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 36

Journal of Agricultural and Food Chemistry

1

Multi-scale structural changes of wheat and yam starches during

2

cooking and their effect on in vitro enzymatic digestibility

3 Shujun Wanga*, Shaokang Wanga, Peng Guoa, Lu Liua, Shuo Wangab*

4 5 6

a

Key Laboratory of Food Nutrition and Safety, Ministry of Education, College of Food

7

Engineering and Biotechnology, Tianjin University of Science & Technology, Tianjin 300457,

8

China

9

b

Beijing Advanced Innovation Center for Food Nutrition and Human Health, Beijing Technology & Business University, Beijing 100048, China

10 11 12 13 14

* Corresponding authors: Dr. Shujun Wang or Dr. Shuo Wang

15

Mailing address: No 29, 13th Avenue, Tianjin Economic and Developmental Area (TEDA), Tianjin

16

300457, China

17

Phone: 86-22-60912486

18

E-mail address: [email protected] or [email protected]

19 20 21 22 1

ACS Paragon Plus Environment


23

ABSTRACT

24

In the present study, the multi-scale structures and in vitro digestibility of wheat and

25

yam starches with different water contents after heating at 100 oC were investigated.

26

After heating for the same time, the degree of gelatinization of both starches increased

27

with increasing water content, followed by the gradual disruption of multi-scale

28

structures of starch granules. At a water content of 37% for wheat and 46% for yam

29

starch, both starches were almost gelatinized completely after heating for 5 min at 100

30

o

31

especially at a water content of above 28%. It is interesting to note that extending heat

32

treatment did not further disrupt the multi-scale structures nor increase the in vitro

33

enzymatic digestibility of both starches with the same water content. In contrast to

34

wheat starch, yam starch showed a higher resistance to heat treatment. From this study,

35

we can conclude that water content plays a more important role in determining the

36

gelatinization behavior and in vitro enzymatic digestibility of starch than the duration

37

of heating.

C. Heat treatment increased greatly in vitro enzymatic digestibility of both starches,

38 39 40

Keywords: starch; water content; duration of heating; multi-scale structure;

41

gelatinization; in vitro enzymatic digestibility

42 43 44 2


Page 2 of 36

Page 3 of 36


45

INTRODUCTION

46

Starch is the main component of many foods and the source of glycemic

47

carbohydrates in the human diet. The rate of digestion and absorption of starch is

48

determined by the state of starch in foods and has a relationship to major

49

nutrition-related health problems.1,2 Starch is a heterogeneous polymer which contains

50

amylose and amylopectin. Amylose is mainly made up of the linear α-1,4-D-glucan

51

chains connected with a small number of branched chains by α-1,6-glycosidic bond.

52

Amylopectin is a moderately branched macromolecule composed of backbone chains

53

and side chains that are linked by an average of 5% of α-1,6-glucosidic bonds.

54

Amylose and amylopectin make up approximately 98-99% dry weight of starch.3-6

55

Native starch has a very complex hierarchical structure, ranging in scale from nano- to

56

micrometer, including glucose units, double helices, crystalline and amorphous

57

lamellae, super helices, blocklets, growth rings and intact granules. Each of the

58

structural units plays an important role in determining starch functionality that relates

59

to food processing and digestion.7

60 61

During heating in the presence of water, starch undergoes a series of sequential phase

62

transitions, including glass transition, gelatinization, and/or melting transition.2,8 The

63

multi-scale structures of starch granules are disrupted during cooking or processing,

64

and the degree of disruption is dependent on water content, heating temperature and

65

length. Gelatinization increases the susceptibility of starch to enzymatic digestion.9-13

66

The relationship between degree of gelatinization and starch digestibility has been 3



67

well studied, mostly on starch systems with high moisture contents.11, 14-16 Most starch

68

in food is cooked or processed with limited water (ratio of water:starch < 2:1, w/w),17,

69

18

70

multi-scale structures. Up to now, there is little information on the changes that starch

71

undergoes during thermal processing under water-limited conditions and how these

72

changes influence the susceptibility of starch to enzymic hydrolysis. While the effect

73

of heat-moisture treatment on physicochemical properties of starch has been studied

74

extensively, these studies mainly aim to improving the functionality of

75

hydrothermally-modified starch. 19, 20

which results in partial gelatinization of starch and incomplete disruption of

76 77

Understanding the effect of cooking or processing parameters on starch digestibility is

78

of great importance for optimization of food processing to manipulate starch

79

digestibility in foods.2 Under water limited conditions, starch is not always fully

80

gelatinized, which increases the complexity of understanding starch digestibility in

81

terms of the extent of structural changes induced by processing. In the present study,

82

the effects of water content (19 to 64%, wt%) and duration of heating at 100 oC on

83

gelatinization behavior and in vitro enzymatic digestibility of wheat and yam starches

84

were examined. To the best of our knowledge, this is the first study to investigate the

85

changes of multi-scale structures and in vitro enzymatic digestibility of starches

86

during heating at 100 oC over such a wide range of water content.

87 88

MATERIALS AND METHODS 4


Page 4 of 36

Page 5 of 36


89

Materials. The grains of hard winter wheat were provided by Lixiahe Agricultural

90

Research Institute, Jiangsu Province, China. Yam tubers were purchased from local

91

market in Tianjin, China. Native wheat starch (NWS) and yam starch (NYS) were

92

isolated from wheat grains and yam tubers according to the method of Wang, Wang,

93

Zhang, Li, Yu, and Wang21 and Ek, Wang, Copeland and Brand-Miller.22 The amylose

94

contents of NWS and NYS, as determined by the method of Chrastil,23 were 27.7 and

95

37.1%, respectively. The moisture content of both starches was about 10%. Glucose

96

oxidase/peroxidase kit (GOPOD format) and Aspergillus niger amyloglucosidase

97

(3260U/mL) were purchased from Megazyme International Ireland Ltd. (Bray Co.,

98

Wicklow, Ireland). α-Amylase (Sigma, EC3.2.1.1, type VI-B from porcine pancreas,

99

13 U/mg) was purchased from Sigma Chemical Co. (St. Louis, MO, USA). All other

100

chemical reagents were of analytical grade.

101 102

Heat treatment of starch-water mixtures. Unlike common heat-moisture treatment,

103

which is often conducted by heating starch-water mixtures in a sealed glass container

104

using an oven,24 heat treatment of starch-water mixtures in the present study was

105

performed as follows. Wheat and yam starches (5 g) were weighed exactly into a

106

polypropylene bag, and a certain amount of distilled water was added to obtain water

107

contents of 19%, 28%, 37%, 46%, 55%, and 64% (w/v, dry weight basis). The starch

108

samples were mixed thoroughly during the addition of water. The bags were sealed

109

and allowed to stand at room temperature for 2 h before heating in a boiling water

110

bath for 5 min, 10 min, 20 min and 30 min. As a control, both native starches were 5



Page 6 of 36

111

placed in the bags and hermetically heated in the same way. After heating, the samples

112

were immediately frozen in liquid nitrogen for about 10 min, freeze-dried, ground into

113

a powder and passed through a 100 µm sieve. As there were no significant differences

114

in structural properties and in vitro enzymatic digestibility between native starch and

115

control samples, only the data for native starch are presented. The samples in the

116

figures were named as NWS (NYS)-water content (%)-heating time (min), which

117

means that native wheat or yam starch with the specified water contents was heated at

118

100 oC for the times indicated.

119 120

Differential scanning calorimetry. Thermal properties of starch samples were

121

analyzed using a differential scanning calorimeter (200 F3, Netzsch, Germany)

122

equipped with a thermal analysis data station. Approximately 3 mg of starch samples

123

were weighed accurately into 40 µL aluminum pans. Distilled water was added with a

124

pipette to obtain a starch: water ratio of 1:5 (w/v) in the DSC pans according to a

125

method described previously.6 The pans were sealed and allowed to stand at room

126

temperature for 12 h before DSC analysis. The pans were heated from 20 to 100 oC at

127

a heating rate of 10 oC /min. An empty aluminum pan was used as the reference. All

128

measurements were performed in triplicate. The degree of gelatinization (DG) of each

129

sample was calculated according to the formula:13, 25

130

DG (%) = (1 −∆H heated starch/∆H native starch) ×100

131

where ∆H

132

enthalpy change of native starch.

heated starch

is the enthalpy change of heated starch, ∆H

6


native starch

is the

Page 7 of 36


133 134

Attenuated

Total

Reflectance-Fourier

transform

infrared

(ATR-FTIR)

135

spectroscopy. The short-range molecular order of double helices in starch was

136

determined using a Thermo Scientific Nicolet IS50 FTIR spectrometer (Thermo

137

Fisher Scientific, USA). Starch (150 mg) was pressed into round tablets and scanned

138

between 4000 and 400 cm-1. The spectra were obtained at a resolution of 4 cm-1 with

139

an accumulation of 32 scans against air as the background. The FTIR spectra were

140

baseline-corrected automatically by OMNIC 8.0 and deconvoluted from 1200 to

141

800cm-1 with a half-bandwidth of 19 cm-1 and an enhancement factor of 1.9. The

142

ratios of absorbances at 1047/1022 cm-1 were obtained to estimate the short-range

143

ordered structure of starch. 26

144 145

Laser confocal micro-Raman (LCM-Raman) spectroscopy. Raman spectra were

146

obtained using a Renishaw Invia Raman microscope

147

Gloucestershire, United Kingdom) equipped with a Leica microscope (Leica

148

Biosystems, Wetzlar, Germany) and a 785 nm green diode laser source was used. The

149

Raman system was calibrated with a silicon semiconductor using the Raman peak at

150

520 cm−1. The spectra from 4000 to 400 cm-1 were collected from at least five

151

different spots with a resolution of approximately 7 cm-1. The full width at half

152

maximum (FWHM) of the band at 480 cm-1 was obtained using the software of WIRE

153

2.0, which is usually used to characterize the change of molecular order during

154

gelatinization or retrogradation.7, 27 7


system (Renishaw,


155 156

X-ray diffraction. X-ray diffraction analysis was performed using a Bruker D8 Focus

157

X-ray diffractometer (Bruker AXS, Germany) operating at 40 kV and 40 mA with Cu

158

Kα radiation (λ=0.154 nm). Starch samples were equilibrated over a saturated NaCl

159

solution at room temperature for one week before analysis. The X-ray diffraction

160

pattern was obtained from 4° to 35° (2θ) at a scanning speed of 1°/min and a step size

161

of 0.02°. The relative crystallinity was quantified as the ratio of the crystalline area to

162

the total area between 4o and 35o (2θ) using the Origin software (Version 8.0,

163

Microcal Inc., Northampton, MA, USA).

164 165

Field-emission scanning electron microscopy. The freeze-dried samples were

166

mounted on a stub with double-sided adhesive tapes, sputter-coated with gold before

167

imaging using a field-emission scanning electron microscope (1530, LEO, Germany).

168

An accelerating voltage of 5 kV was used during imaging.

169 170

In vitro starch digestion. In vitro enzymic digestion of starch was determined

171

according to the method described elsewhere.28 At specified time points during

172

digestion (from 0 min to 120 min), an aliquot (0.05 mL) of the hydrolysate was

173

withdrawn and mixed with 0.95 mL of 95% ethanol to deactivate the enzymes. The

174

amount of glucose released in the digestion solution was measured using the

175

Meagazyme GOPOD kit. The percentage of hydrolysed starch was calculated by

176

multiplying the glucose content with a factor of 0.9. The starch digestograms were 8


Page 8 of 36

Page 9 of 36


177

obtained by plotting the percentage of starch digestion as a function of hydrolysis

178

time.

179 180

Statistical analysis. All analyses were performed at least in triplicate and the results

181

are reported as the mean values and standard deviations. One way analysis of variance

182

(ANOVA) followed by post-hoc Duncan’s multiple range tests (p

Multiscale Structural Changes of Wheat and Yam Starches during

Recommend Documents