Subscriber access provided by Iowa State University | Library
Food and Beverage Chemistry/Biochemistry
Structural changes of starch-lipid complexes during postprocessing and their effect on in vitro enzymatic digestibility Renbing Qin, Jinglin Yu, Yufang Li, Les Copeland, Shuo Wang, and Shujun Wang J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.8b06371 • Publication Date (Web): 11 Jan 2019 Downloaded from http://pubs.acs.org on January 12, 2019
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 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 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.
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 34
Journal of Agricultural and Food Chemistry
1
Structural changes of starch-lipid complexes during post-processing
2
and their effect on in vitro enzymatic digestibility
3 4
Renbing Qinab, Jinglin Yua, Yufang Liab, Les Copelandc, Shuo Wangad*, Shujun Wangab*
5 6
a State
Key Laboratory of Food Nutrition and Safety, Tianjin University of Science &
7
Technology, Tianjin 300457, China
8 9
b School
of Food Engineering and Biotechnology, Tianjin University of Science &
10
Technology, 300457, China
11 12
c
The University of Sydney, Sydney Institute of Agriculture, School of Life and
13
Environmental Sciences, NSW Australia 2006
14 15
d Tianjin
Key Laboratory of Food Science and Human Health, School of Medicine, Nankai
16
University, Tianjin, 300071, China
17 18
* Corresponding authors: Dr. S Wang
19
Mailing address: No 29, 13th Avenue, Tianjin Economic and Developmental Area (TEDA),
20
Tianjin 300457, China
21
Phone: 86-22-60912486
22
E-mail address:
[email protected] 23 24 25
ACS Paragon Plus Environment
Journal of Agricultural and Food Chemistry
26
Abstract: The effects of cooking and storage on the structure and in vitro enzymatic
27
digestibility of complexes formed between fatty acids and debranched Hi-amylose
28
starch (DHA7-FA) were investigated for the first time. Cooking decreased greatly the
29
crystallinity of DHA7-lauric acid (LA) and DHA7-myristic acid (MA) complexes, but
30
had little effect on the crystallinity of DHA7-palmitic acid (PA) and DHA7-stearic
31
acid (SA) complexes. Cooking increased enthalpy change (ΔH) values and
32
short-range molecular order of DHA7-FA complexes. Cooking decreased in vitro
33
enzymatic digestibility of DHA7-FA complexes, with the extent of the effect
34
decreasing with increasing fatty acid chain length. Holding the samples 4 oC for 24 h
35
after cooking did not affect greatly the long- and short-range molecular order nor in
36
vitro enzymatic digestibility of DHA7-FA complexes. From this study, we conclude
37
that cooking disrupted the long-range crystalline structure of DHA7-LA and
38
DHA7-MA complexes, but enhanced the short-range molecular order of all of the
39
DHA7-FA complexes. The latter effect accounted mainly for the reduced in vitro
40
enzymatic digestibility of DHA7-FA complexes.
41 42
Keywords: Hi-amylose starch; amylose-fatty acid complexes; cooking; structure; in
43
vitro digestibility
ACS Paragon Plus Environment
Page 2 of 34
Page 3 of 34
Journal of Agricultural and Food Chemistry
45
INTRODUCTION
46
Starch and lipids are major components of foods that play important roles in their
47
texture, flavor and nutritional quality. Amylose-lipid complexes can be formed during
48
food processing or on subsequent cooling and storage.1 The formation of these
49
complexes has attracted much attention over many years because of their impact on
50
starch rheological properties,2-3 retrogradation,4 digestibility in vivo5 and enzymatic
51
digestibility in vitro.6-7 Complexes between amylose and lipids are also now classified
52
as a type of resistant starch (RS), namely RS5.8-10 RS escapes digestion in the small
53
intestine and enters the large intestine, where it is fermented by the gut microbiota to
54
produce short-chain fatty acids (SCFAs),11-16 which play an important role in
55
intestinal health and the general well-being of the host.17-25
56 57
Due to its many supposed human health benefits, increasing the RS content in foods is
58
the subject of much research26-28. Previous studies have focused mainly on the
59
preparation of RS by different methods, or its formation during processing of
60
ingredients into foods.29-34 Little information is available on the effect of further
61
handling (i.e., “post-processing”) of foods on the properties of RS, and in turn the
62
textural and nutritional value of these food products. Many cooked starchy foods,
63
such as Western oven-baked breads, Chinese steamed breads, some frozen foods or
64
rice dishes, are reheated before being consumed by humans. Hence, it is of interest to
65
increase our understanding of the changes that RS undergoes during this
66
“post-processing” stage. Amylose-lipid complexes, which are now considered an
ACS Paragon Plus Environment
Journal of Agricultural and Food Chemistry
67
important resistant starch form (RS5) that can occur in processed foods, and that can
68
be formed experimentally under controlled conditions, provides a good model system
69
to investigate structural and functional changes of RS after reheating. Thus, the
70
objective of this study was to investigate the effects of cooking and storage on
71
structure-function relationships of RS5 relevant to its in vitro enzymatic digestibility.
72
The results will be of significance for better understanding the changes of RS5 during
73
post-processing and for better control of starch digestion during food processing.
74 75
MATERIALS AND METHODS
76
Materials
77
High-amylose maize starch VII (HA7, amylose content 68.7%) was a gift of
78
Ingredion Inc. (Westchester, IL, USA). Lauric acid (C12:0, LA), myristic acid (C14:0,
79
MA), palmitic acid (C16:0, PA), stearic acid (C18:0, SA), pullulanase (EC 3.2.1.41,
80
activity of pullulanase was 1498 NPUN/mL (New Pullulanase Unit Novo).) and
81
α-amylase (EC 3.2.1.1, type VI-B from porcine pancreas, 13 U/mg) were purchased
82
from Sigma Chemical Co. (St. Louis, MO, USA). The glucose oxidase/peroxidase kit
83
(GOPOD format) and Aspergillus niger amyloglucosidase (3260 units/mL) were
84
purchased from Megazyme International Ireland, Ltd. (Bray Co., Wicklow, Ireland).
85
All other chemicals were of analytical grade and were from Sigma-Aldrich Chemical
86
Corporation (Shanghai, China).
87 88
Preparation of RS5
ACS Paragon Plus Environment
Page 4 of 34
Page 5 of 34
Journal of Agricultural and Food Chemistry
89
RS5 was prepared according to the method of Hasjim et al.8 with minor modifications
90
as follows. The HA7 slurry (10% w/v) in 0.2 M sodium acetate buffer (pH 5.0) was
91
heated at 130 °C for 60 min to completely gelatinize the starch. The starch paste was
92
cooled to 60 °C and debranched by pullulanase (80 NPUN /g starch) for 12 h with
93
agitation. The debranched starch suspension was re-heated at 130 °C for 30 min, after
94
which the respective fatty acid (FA; 10% w/w, dry starch basis) was added to the
95
suspension and maintained at 90 °C for an additional 1 h. The mixtures were cooled
96
to 25 °C with stirring for 2 h. The resulting starch-lipid complex was recovered by
97
centrifugation (2000 g, 20 min) and washed with 50% ethanol. This step was repeated
98
three times to remove uncomplexed FAs and to obtain salt-free complexes. The
99
amylose-FA complexes, referred to generically as DHA7-FA, were freeze-dried,
100
ground using a mortar and pestle, and stored at 4 °C until further analysis.
101 102
Post-processing of RS5
103
Post-processing of RS5 was performed according to a method described previously35
104
with modifications. RS5 (1 g) was weighed accurately into a polypropylene bag and
105
mixed thoroughly with 3 ml of distilled water. The bags were sealed and allowed to
106
stand at room temperature for 2 h before heating in a boiling water bath for 10 min.
107
Some of the heated samples (designated DHA7-FA-100) were frozen immediately in
108
liquid nitrogen for about 10 min, whereas others were kept at 4 °C for 24 h
109
(DHA7-FA-100-4) before freezing. Both sets of samples were freeze-dried, ground
110
into powders, and passed through a 100 μm sieve.
ACS Paragon Plus Environment
Journal of Agricultural and Food Chemistry
111 112
X-ray Diffraction Analysis (XRD)
113
Relative crystallinity of the RS5 samples was determined by an X-ray diffractometer
114
(D8 Advance, Bruker, Germany) operating at 40 kV and 40 mA with Cu-Kα radiation
115
(λ= 0.15406 nm). The samples were equilibrated over a saturated NaCl solution at
116
room temperature for 7 days before analysis. The XRD spectra were obtained from 4
117
to 35° (2θ) at a scanning rate of 2°/min and a step size of 0.02°. The relative
118
crystallinity was calculated as the ratio of the crystalline area over the total area under
119
the X-ray diffractograms using the software of TOPAS 5.0 (Bruker, Germany).
120
V-type crystallinity and B-type crystallinity were calculated respectively as the ratio
121
of area of V-crystal peaks (7.5, 12.9 and 19.8°) and B-crystal peaks (5.6, 16.9, and
122
22.6°) to the total area under XRD curves.
123 124
Laser Confocal Micro-Raman Spectroscopy
125
Raman spectra were recorded using a Renishaw Invia Raman microscope system
126
(Renishaw, Gloucestershire, U.K.) equipped with a Leica microscope (Leica
127
Biosystems, Wetzlar, Germany), and a 785 nm green diode laser source was used.
128
Each spectrum of starch samples (4000-400 cm-1) was collected from at least five
129
different spots with a resolution of approximately 7 cm-1. The full width at half
130
maximum (FWHM) of the band at 480 cm-1 was calculated using the software of
131
WIRE 2.0, which is taken as an indicator of the short-range ordered structure in
132
starch.36
ACS Paragon Plus Environment
Page 6 of 34
Page 7 of 34
Journal of Agricultural and Food Chemistry
133 134
Differential Scanning Calorimetry (DSC)
135
Thermal properties of samples were measured using a Differential Scanning
136
Calorimeter (200F3, Netzsch, Germany) equipped with a thermal analysis data
137
station. RS5 samples (3 mg) were weighed accurately into 40 μL aluminum pans, and
138
deionized water was added to give a water/starch ratio of 3:1 (w/w). The RS5-water
139
mixtures were allowed to stand overnight at room temperature before DSC
140
measurement. The samples were heated from 20 to 135 °C at a heating rate of
141
10 °C/min. An empty aluminum pan was used as the reference. The values of the
142
thermal transition temperatures (onset, To; peak, Tp; conclusion, Tc) and enthalpy
143
change (H) of RS5 were determined from the data recording software.37
144 145
In Vitro Enzymatic Digestibility of RS5
146
The in vitro digestibility of RS5 samples was analyzed according to the procedure of
147
Wang et al.38 Starch (100 mg, dry weight basis) was suspended in 4.0 mL of 0.1 M
148
sodium acetate buffer (pH 5.2) and 1.0 mL of freshly prepared enzyme solution
149
containing 1645 units of amylase and 41 units of amyloglucosidase was added. The
150
starch/enzyme mixtures were incubated at 37 °C with stirring at 260 rpm for 3 h. At
151
specific time points (from 0 to 180 min), an aliquot (0.05 mL) of the hydrolysate was
152
withdrawn and mixed with 0.95 mL of 95% ethanol to deactivate the enzymes. The
153
amount of glucose released was determined using the Megazyme GOPOD kit. The
154
percentage of hydrolyzed starch was calculated by multiplying the glucose content
ACS Paragon Plus Environment
Journal of Agricultural and Food Chemistry
155
with a factor of 0.9. Starch classifications based on the rate of hydrolysis were:
156
rapidly digested starch (RDS, digested within 20 min), slowly digested starch (SDS,
157
digested between 20 and 120 min) and resistant starch (RS, undigested starch after
158
120 min). The hydrolysis index (HI) was derived from the ratio between the area
159
under the hydrolysis curve (0~180 min) of each RS5 samples and the corresponding
160
area of white bread expressed as a percentage over the same period. From the HI
161
obtained in vitro, the estimated glycemic index (eGI) value was then calculated using
162
the empiric formula proposed by Granfeldt et al.39
163
eGI = 8.198 + 0.862 × HI.
164 165
Statistical Analysis
166
All analyses were performed at least in triplicate, and the results are reported as the
167
mean values and standard deviations. In the case of XRD, only one measurement was
168
performed. One way analysis of variance (ANOVA) followed by post-hoc Duncan’s
169
multiple range tests (p 0.05). ND, not detected To: transition onset temperature, Tp: transition peak temperature, ∆H: transition enthalpy *indicates type I complex, +indicates type II complex.
ACS Paragon Plus Environment
Page 33 of 34
563 564
565 566 567 568 569
Journal of Agricultural and Food Chemistry
Table 3. In vitro digestibility and estimated glycemic index of RS5 samples before and after cooking or followed by storage Samples
RDS (%)
SDS (%)
RS (%)
HI
DHA7-LA
25.9±1.0f
27.6±1.3f
46.4±0.5b
51.4±0.5i
52.5±0.4i
DHA7-LA-100
22.9±0.3a
18.8±0.8b
58.4±1.1fg
37.6±0.9a
40.6±0.8a
DHA7-LA-100-4
23.3±0.6ab
17.4±0.1ab
59.4±0.6g
38.0±0.3ab
40.9±0.3ab
DHA7-MA
25.2±0.6def
31.0±1.6g
43.9±1.0a
53.6±0.6j
54.4±0.5j
DHA7-MA-100
24.7±0.8cde
23.0±0.4d
52.3±0.5d
45.0±0.5f
47.0±0.4f
DHA7-MA-100-4
24.3±0.6bcd
21.0±0.6c
54.7±0.3e
43.7±0.2e
45.8±0.2e
DHA7-PA
25.8±0.3ef
25.3±0.5e
48.9±0.8c
50.3±0.6h
51.6±0.5h
DHA7-PA-100
24.2±1.1bcd
23.2±1.2d
52.6±0.3d
44.9±0.3f
46.9±0.2f
DHA7-PA-100-4
24.8±0.6cdef
23.3±1.2d
51.9±0.6d
46.1±0.9g
47.9±0.8g
DHA7-SA
24.6±0.2cde
17.9±0.3ab
57.5±0.1f
42.2±0.3d
44.6±0.3d
DHA7-SA-100
23.6±0.9abc
18.0±1.2ab
58.4±1.0fg
38.7±0.4bc
41.6±0.4bc
DHA7-SA-100-4
23.9±0.4abcd
16.4±1.4a
59.7±1.1g
39.4±0.5c
42.2±0.5c
eGI
Values are means ± SD. The letters a, b, c, d, e, f, g, h, i, j represent a significant difference between the data in the same column (p< 0.05);
570 571 572 573 574 575 576 577 578 579 580 581 33
ACS Paragon Plus Environment
Journal of Agricultural and Food Chemistry
582 583 584 585 586 587 588 589 590 591 592 593 594 595 596
Table of Contents Graphic
597
34
ACS Paragon Plus Environment
Page 34 of 34
