Effects of Starch on the Digestibility of Gluten under Different Thermal

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Food and Beverage Chemistry/Biochemistry

Effects of starch on the digestibility of gluten under different thermal processing conditions Wenjun Wen, Shijie Li, Ying Gu, Shuo Wang, and Wang junping J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.9b01063 • Publication Date (Web): 26 Apr 2019 Downloaded from http://pubs.acs.org on April 27, 2019

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Journal of Agricultural and Food Chemistry

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Effects of starch on the digestibility of gluten under

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different thermal processing conditions

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Wenjun Wen a, Shijie Li a, Ying Gu a, Shuo Wang b*, Junping Wang a*

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a

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Technology, 29 The Thirteenth Road, Tianjin Economy and Technology

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Development Area, Tianjin, 300457, P.R. China

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b

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300350, P.R. China

State Key Laboratory of Food Nutrition and Safety, Tianjin University of Science &

Medical college, Nankai University, No.38 Tongyan Road, Jinnan District, Tianjin,

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*Corresponding Authors: [email protected]; Fax: (+86 22) 60912487; Tel: (+86

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22) 60912487

ACS Paragon Plus Environment


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Abstract

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Gluten and starch are the primary ingredients of the wheat. The complex reaction

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between the gluten and starch will occur during the thermal food processing, which will

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affect the digestibility. The effects of proteins on the digestibility of starch have been

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reported, but the effects of starch on the digestibility of proteins have not been well-

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researched. In this paper, the effects of starch on gluten digestion during the heating

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process were studied by the gluten-starch simulated system, and it was found that starch

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can enhance gluten digestion. When the complex of gluten-starch being 1:1 is heated at

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100°C, the digestibility of gluten is higher, and more low-molecular weight peptides

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are produced. Results from the digestibility and digestion-peptide mapping of the

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gluten-starch complex at different conditions showed that the addition of starch during

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processing enhanced the digestion performance of gluten. Meanwhile, the secondary

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structure, intrinsic fluorescence, and microscopic structure of the gluten-starch complex

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were investigated to understand the mechanism of the enhancement. The digestion

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performance is related to the secondary structure variation during the thermal

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processing caused by hydration increase and disulfide bonds reduction. The gluten-

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starch-complex spatial structure is looser than gluten after heating, which could expose

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more protease cleavage sites. These results suggest that starch can protect gluten from

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aggregation in water and destroy the spatial structure of gluten with the assistant of

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heating, exposing more cleavage sites and enhancing gluten digestion.

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Keywords: gluten; gluten-starch simulated system; interaction between gluten

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and starch; protein structure analysis; digestibility; thermal processing


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Introduction

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Wheat is one of the most widely cultivated cereals in the world. The major constituents

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of wheat grain are starch (70−80% dry weight) and proteins (10−15% dry weight).1

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Wheat is an important source of protein supplementation, especially in countries

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dominated by plant-based food. Protein provides nutrition for by digestion, meanwhile,

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digestion can induce allergies in some people,2-4 so digestibility is an important

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indicator for the protein nutrition evaluation. Gluten has complex spatial structure,

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meanwhile the proportions of glutamine and proline are about 38% and 20%5 so it is

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more difficult to digestion in the human digestive tract. 6 Protein digestion is influenced by the other components in food (such as polyphenols

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7-9

or other food matrices 10-13) and processing conditions.14-17 The processing can cause

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very complex reactions between food components, which can result to significant

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changes in the digestibility of food components.

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Thermal processing is the important food process. Under the thermal processing, the

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gluten interacts with other components result to spatial structure undergoing changes,

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which can influence the digestibility. There are various interactions between starches

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and proteins, and the effects of proteins on the digestibility of starches have been

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reported,18-22 but few reports exist concerning the effects of starch on protein digestion,

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particularly gluten. In hence, the effects of starch on the digestion of gluten under

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thermal processing needs further investigation, it is great significance to fully

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understand the digestibility of proteins in different foods after thermal processing and

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the nutritional value of proteins in different thermal processed foods.



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The purpose of this study was to investigate the effects of starch on gluten digestion

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and elucidate the interactions between starch and gluten. Based on the digestion,

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absorption and utilization of gluten, we could evaluate the nutritional value of wheat

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products processed through different methods. This study could also serve as a

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reference to improve processing adaptability to increase the digestion and utilization of

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wheat.

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This study will examine the gluten digestive ability in the gluten-starch complex

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formed by wheat starch and gluten at different temperatures and gluten-starch

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proportions in a simulated system. The digestive performance will be indicated by the

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digestibility and peptide mapping after digestion to characterize the effects of starch on

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gluten digestion. The digestibility was measured by the o-phthalaldehyde method

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(OPA), and the peptide mapping was determined by Matrix-Assisted Laser Desorption/

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Ionization Time of Flight Mass Spectrometry (MALDI-TOF-MS). The secondary

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structure was determined by Fourier Transform infrared spectroscopy (FTIR) to study

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the connection between gluten secondary structures and gluten digestibility. The

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difference in the spatial structure of the gluten in different conditions was observed by

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scanning electron microscopy (SEM) to explain the mechanism of starch affecting

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gluten digestion from a spatial perspective. The determination of the intrinsic

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fluorescence of gluten-starch complexes could reveal the mechanism from the protease

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cleavage sites.

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Materials and methods

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Commercial wheat gluten and starch were purchased from the market. The water used


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in this study was made by Milli-Q Ultrapure Water Systems. All chemicals used were

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of analytical grade unless otherwise specified. Pepsin from porcine gastric mucosa

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(>2500 U/mg), trypsin from porcine pancreas (1655 U/mg) and chymotrypsin (>40

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U/mg) were purchased from Sigma-Aldrich Chemical Corporation. The ZipTip C18

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pipette tip was purchased from Merck Millipore Ltd.

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Sample preparation

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Gluten-starch simulated system preparation. Gluten and starch (1.00±0.02 g) were

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mixed with deionized water (10 mL) in different gluten-starch proportions (1:9, 2:8,

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3:7, 4:6, 5:5, 6:4,7:3,8:2, 9:1, w/w). For a large portion of wheat products processed at

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100°C in China, so the 40, 60, 80, and 100°C were selected as heating temperature.

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Different gluten-starch proportions mixture were heated with magnetic stirring for 10

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min, especially the mixture that was treated at 20°C in a constant temperature incubator.

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The gluten as a control was also heated at the same temperatures. The samples after

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heating were lyophilized and ground to powder for further analysis.

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Simulated digestion of sample

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The simulated digestive fluid was configurated according to Gianluca Picariello et al.23

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The weight of gluten-starch complex for digestion was calculated and weighed

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according to the 50 mg gluten in gluten-starch complex to ensure the enzyme hydrolysis

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substrate was consistent. The sample was dissolved in 5 mL simulated gastric fluid

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including 35 mM NaCl, 2.5 mM CaCl2 and pepsin (182 U/mg protein) acidified with

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HCl at pH 2 and digested at 37°C for 1 h at 50 rpm in a constant temperature incubator.

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The in vitro duodenal digestion was carried out on the products from stomach digestion



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supplemented with NaCl, CaCl2, Tris, bile salts, trypsin, and chymotrypsin. The final

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concentrations within the mixture were 7.4 mM bile salts, 7.6 mM CaCl2 and 20.3 mM

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Tris, trypsin (40 U/mg protein) and chymotrypsin (0.5 U/mg protein). The mixture was

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digested at 37°C for 4 h. The reaction was stopped by heating for 5 min in a boiling

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water bath. Digested tubes were centrifuged, and the supernatants were used to quantify

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the degree of hydrolysis (DH).

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Determination of sample digestibility.

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The method was modified according to Wu et al.24 Briefly, hydrolysate aliquots were

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diluted 1/20 in 100 mM sodium bicarbonate and mixed with OPA reagent (100 mM

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sodium tetraborate, 0.01% SDS, 0.05 mg/mL OPA, 0.05 mg/mL DTT) in a 96-well

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plate. The plate was incubated for 10 min at room temperature before measuring

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fluorescence emission (excitation: 340 nm, emission: 450 nm) using a plate reader

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(Varioskan LUX, Thermo Scientific, Waltham, MA, USA). Different concentrations of

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tryptophan (0.001, 0.005, 0.010, 0.020, 0.050, 0.060 mmol/mL) were configured for

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the standard curve. Digestibility is determined by calculating the ratio of free amino

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groups after digestion to the total amino acid content of the protein. All determinations

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were conducted in triplicate. According to Paridhi et al.,25 The DH, or extent of

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proteolytic hydrolysis, was calculated using the following equation:

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DH (%) = (hs/htotal) ×100%

(1)

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where hs is defined as the mmol of free amine groups per gram of protein in the

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sample, and htotal is the mmol of free amino groups per gram of protein, assuming

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complete hydrolysis of the protein (7.96 mmol/g protein). All tubes (representing triple


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samples from above) were measured three times.

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MALDI-TOF-MS analysis of sample digest

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Ten microliters of sample was absorbed by Zip tip C18 pipette tip which was pre-

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equilibrated with acetonitrile and 0.1% TFA. The salt was washed by 0.1% TFA, and

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the target peptides were eluted by the solvent of acetonitrile-water (20:80, v/v). One

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microliter of desalting sample was added to the ground steel BC target (MTP 384,

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Bruker, Bremen, Germany), then 1 μL of the CHCA (α-Cyano-4-hydroxy cinnamic

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acid) matrix solution was added onto the sample.

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MALDI-TOF mass spectra were obtained from an UltrafleXtreme TOF-TOF mass

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spectrometer (Bruker, Bremen, Germany), operating in reflector mode. The m/z mass

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range was 0–5000, and laser intensity was 60%. External calibration was performed

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using Peptide Calibration Standard II (Bruker). Every determination was performed

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four times. The results were analyzed by flex Analysis Batch Process, and the data was

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represented by heat map.

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FTIR analysis of sample

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The FTIR spectra of samples were obtained using a Tensor 27 FTIR spectrometer

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(Bruker, Germany) equipped with a KBr beam splitter and a DLaTGS detector. The

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samples were mixed with KBr powder at a ratio of 1:150 (w/w). After mixing and

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grinding, the fine powders were pressed into the transparent pellets and examined by

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the transmission method. The spectra were scanned from 4000 to 400 cm−1, with an

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accumulation of 64 scans at a resolution of 4 cm−1.

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Intrinsic fluorescence measurement of sample



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Intrinsic fluorescence of proteins is mainly attributed to tryptophan and tyrosine, which

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are hydrophobic amino acids. For measuring intrinsic fluorescence, 5.00 ± 0.02 mg

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sample was dispersed in 1 mL water, centrifuged at 10000 rpm for 5 min, then excited

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at 280 nm, and the fluorescence intensity was recorded at 343 nm (LUMINA

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Fluorescence Spectrometer, Thermo Scientific, Waltham, MA, USA). This was the

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maximum intrinsic fluorescence intensity based on a scan from 295–400 nm.

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Scanning electron microscopy

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The microstructural analysis of the samples was carried out by scanning electron

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microscopy (HITACHI, Japan). The freeze-dried and milled samples were exposed to

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gold sputtering before been photographed. The images were captured and stored at a

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resolution of 1280 x 1024 pixels.

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Statistical analysis

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The experimental data were processed using Origin 8.5 software. Significant

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differences among experimental mean values including the digestibility and the

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intrinsic fluorescence intensity were analyzed by one-way analysis of variance

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(ANOVA) coupled with the Duncan’s test at a statistical significance level of 95% (p

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< 0.05).

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Results

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Gluten digestibility

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Effects of starch on gluten digestibility at different proportions

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Nine different proportions (1:9, 2:8, 3:7, 4:6, 5:5, 6:4,7:3,8:2, 9:1, w/w) of the gluten-

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starch complex were selected to investigate the effects of starch on gluten digestibility


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at different proportions with gluten as a control. The gluten digestibility was determined

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after heating to 100°C, and the results are shown in Fig. 1(a). It was found that after the

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addition of starch, the digestibility of the gluten is higher than without starch. When the

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gluten-starch ratio was from 1:9 to 5:5, the digestibility increased with the increase of

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gluten ratio. When the ratio of gluten-starch was from 5:5 to 9:1, the digestibility

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decreased slightly. The maximum digestibility was obtained at a gluten-starch ratio of

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5:5. The results indicated that the starch could promote the digestion of the gluten, but

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the promoting effect is impacted by different gluten-starch ratios. According to the

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results, we selected the proportion of 5:5 for further research.

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Effects of starch on gluten digestibility at different temperatures

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After having investigated the effects of different gluten-starch ratios on gluten

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digestibility, different temperatures were selected to study the changes of gluten

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digestibility during temperature increase. In this study, selection of 5 gluten-starch

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complexes treated at 20, 40, 60, 80 and 100°C was used to explore the effects of starch

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on gluten digestibility at different temperatures, with the gluten treated at same

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temperatures as control. The results are shown in Fig. 1(b). It was found that the

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digestibility of gluten was higher than gluten-starch complexes when they were treated

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at 20°C and 40°C, but the results were opposite at 60°C, 80°C and 100°C. However,

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when the gluten was heated to 100°C alone, the digestibility was the lowest, while the

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gluten-starch complex had the highest digestibility after heating to 100°C. That means

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heating the gluten alone inhibits gluten digestion, and the starch also inhibits the

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digestion of the protein when the heating temperature is lower than 60°C. Otherwise,



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the starch could increase the digestibility when heating temperature increases.

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Peptide mapping after digestion

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The peptide mapping of gluten-starch complexes at different proportions

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The peptide mapping digested by gluten-starch complex at different proportions was

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compared with the gluten as a control. The MS spectrum is shown in Fig. S1. The

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peptide contents in the range of 700–2500 Da were richer than other ranges at all

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proportions (Fig. 2). Conversely, the peptide mapping of blank was richer from 2000

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to 4000 Da, which indicated that the low molecular weight peptide digestion was

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affected by starch, but the effects were not significantly correlated with the proportion

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of gluten-starch. When the proportion of gluten-starch was close to 1, the contents of

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peptide ranging from 2500 to 3000 Da were higher than others, which means that the

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gluten digests tended to produce more peptides when the content of starch was close to

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gluten.

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The peptide mapping of gluten-starch complex at different temperatures

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The peptide mapping of the gluten-starch complex digested at different temperatures

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was compared to gluten, and the peptides MS spectrum is shown in Fig. S2 and Fig.

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S3. The heat map of peptides is shown in Fig. 3. The peptides molecular ranged from

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700 to 4400 Da. According to the heat map, when the gluten-starch complex was treated

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at 20°C, the peptides abundance was lower than other temperatures, and the peptides

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abundance increased with the heating temperature increase (Fig.3(a)). However, When

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the gluten was treated at 20°C, the peptides abundance was higher than other

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temperatures, and the peptide variety decreased when the heating temperature increased


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(Fig.3(b)). The abundance of peptides ranging from 1300 to 2000 Da changed

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insignificantly between gluten and gluten-starch complex, indicating that the peptides

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digestion within this range are not significantly affected by starch. Specifically, the

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peptides from gluten were mainly concentrated in the range of 1600–3000 Da, while

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the peptides from the gluten-starch complex concentrated from 700 to 2000 Da, which

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showed that the starch can improve the digestive performance of gluten, especially the

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production of low molecular peptides.

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The change of gluten secondary structures

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The FT-IR spectra of different samples was shown in Fig. S4(gluten-starch complex at

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different proportions), Fig. S5(gluten-starch complex at different temperatures), Fig.

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S6(gluten at different temperatures). When heating was applied, the secondary

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structures of gluten were mainly determined by the amount and balance of chain

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entanglements, hydrogen bonds, hydrophobic interactions and SS bridges.26 FTIR is

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one of the methods for the protein secondary structures analysis, in which the

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characteristic absorption spectrum of the protein that can reflect the secondary structure

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of the protein is the amide I band (1600 to 1700 cm-1). For gluten, α-helixes are present

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in the N- and C-terminal domains, while β-turns and β-sheets are in the central repetitive

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domain.27 These central repeat domains containing proline and tyrosine residues could

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form hydrophobic interactions. FTIR measurements were performed on the gluten-

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starch complex at different proportions. The results showed that the proportion of β-

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turns increased with increasing gluten fraction, whereas the proportion of random coils

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decreased with increasing gluten fraction, but the changes of β-sheet and α-helix are



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not obvious (Fig. 4(a)). Furthermore, the secondary structures of the gluten-starch

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complex at different temperatures were different (Fig. 4(b)). The β-turn proportion

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increased while temperature increased, but the proportions of β-sheets and α-helixes

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decreased with increasing temperature. For the gluten (Fig. 4(c)), with increasing

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temperature, the β-turns and random coils decreased while the β-sheets and α-helixes

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increased.

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The change of gluten morphology features

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Fig. 5 shows the morphology features of gluten and gluten-starch complex (5:5, w/w)

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at different temperatures. When mixed with starch, gluten generated many cavities on

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the surface as the absorption sites of starch to form the gluten-starch complex. In the

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complex, the gluten structure was unchanged with increasing temperature obviously,

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but the starch gradually swelled as the temperature increased. At 80°C, the starch has

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been completely gelatinized and separated from the gluten surface, inducing gluten to

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exhibit a porous structure. Especially, when the complex was heated to 100°C, the

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spatial structure of the gluten had been destroyed to be lamellar. However, when the

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gluten was heated alone, its structure was nearly invariable at different temperatures,

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even after heating to 100°C.

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The change of gluten intrinsic fluorescence

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The fluorescence spectra of different samples was shown in Fig. S7(gluten-starch

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complex at different proportions), Fig. S8(gluten-starch complex at different

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temperatures), Fig. S9(gluten at different temperatures). Nine different proportions (1:9,

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2:8, 3:7, 4:6, 5:5, 6:4,7:3,8:2, 9:1, w/w) of the gluten-starch complex were selected to


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investigate the effects of starch on the intrinsic fluorescence of gluten at different

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proportions with gluten as a control. The fluorescence spectra of gluten-starch complex

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at different proportions was shown in Fig. S10. The results shown in Fig. 6(a) reveal

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that the intrinsic fluorescence intensity of the gluten-starch complex is higher than

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gluten. When the proportions of gluten-starch were from 1:9 to 5:5, the fluorescence

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intensity increased with the increase of gluten ratio. The maximum intensity was

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obtained at a gluten-starch ratio of 5:5, and the minimum intensity was obtained from

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gluten. When the ratios were 7: 3, 8:2 or 9:1, the fluorescence intensities were stable.

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Compared to the digestibility of gluten-starch complex, the variation of intrinsic

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fluorescence intensity at different proportions resembles the digestibility variation.

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Selection of 5 gluten-starch complexes treated at different temperatures (20, 40, 60, 80

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and 100°C) were used to measure intrinsic fluorescence at different temperatures, with

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the gluten treated at the same temperatures as control. The fluorescence spectra of

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gluten-starch complex and gluten heated at different temperatures are shown in Fig.

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S11 and Fig. S12. The fluorescence intensity change is shown in Fig. 6(a). After the

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gluten–starch complex was heated at 60°C, the intrinsic fluorescence intensity of

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gluten-starch complex was higher than gluten, especially at 100°C. However, there are

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opposite results at 20°C and 40°C. The trends of temperature effects on digestibility

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and intrinsic fluorescence are similar.

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Discussion

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The effect of starch on gluten digestion was investigated by heating the gluten-starch

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complexes at different temperatures and proportions. According to the digestibility of



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gluten and the peptide mapping after digestion for different ratios of gluten to starch,

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the digestibility at 1:9, 2:8 and 3:7 were significantly lower than that of other ratios,

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and the highest digestibility was obtained when the ratio of gluten to starch was 4:6,

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5:5, and 6:4. Then we selected gluten-starch (w/w, 5/5) for further experiments to

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illustrate the change during different heating temperatures. Compared to the

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digestibility and the peptide mapping after digestion of gluten at different temperatures,

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the gluten digestion performance at 20°C was better than other temperatures, indicating

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that heat treatment inhibited gluten digestion. However, the digestive performance of

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gluten heated with starch at 100°C was better than without starch, which indicated that

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adding starch during the gluten processing promoted gluten digestion.

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In gluten, it was found that the amount of β-sheets decreased with increasing

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hydration level,28 which is in agreement with the results in ω-gliadin.29 At high

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hydration, β-sheets were replaced with β-turns.30 The decreased β-sheet and increased

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β-turn suggested that interaction between gluten and starch increased gluten hydration.

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Previous research has indicated that the disulfide bonds have an effect on the

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conformation of gluten, and the α-helix structure decreased with the reduction of

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disulfide bonds.31 The decreased α-helixes suggest that interaction between gluten and

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starch decreased the disulfide bonds. Analyzing the secondary structure and the

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digestibility, β-sheets and α-helixes were negatively correlated with gluten digestibility,

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while β-turn ratio was positively correlated with protein digestibility at different

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temperature treatments. These findings illustrate that the effect of starch on gluten

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digestibility is mainly related to gluten hydration and disulfide bonds at different


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temperatures. According to the “loop and train” model, random coil structures in the

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glutenin, which are highly compacted and stabilized by hydrogen bonding.27 Under an

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intermediate moisture content environment, hydrogen bonds formed, with competition

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between glutamine side chains and water and lead to the formation of “loops” segments

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which are composed of β-turn structures. Thereby, the proportion of β-turns increased

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with increasing gluten fraction, whereas the proportion of random coils decreased with

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increasing gluten fraction, which demonstrates that the different ratios of gluten to

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starch have an effect on hydrogen bonding. Analyzing the secondary structure with the

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digestibility at different proportions of gluten-starch complex, random coils were

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negatively correlated with the digestibility, while the β-turns were positively correlated

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with gluten digestibility, suggesting that the interaction between gluten and starch

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affected the gluten digestibility by reducing hydrogen bonding.

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From the SEM image, when the gluten-starch complexes were heated at low

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temperatures, starch was adsorbed on the surface of the gluten, which might cause the

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enzymatic cleavage sites on the gluten surface to be occupied by the starch, resulting in

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less digestibility than unheated gluten. After gluten was heated to 100°C, the surface of

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gluten aggregated due to hydrophobic interaction,24 which induced the hydrophilic

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amino acids to become exposed on the surface of gluten. However, the hydrophilic

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amino acids are not digestive cleavage sites. Heating gluten to 100°C alone decreased

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gluten digestibility. The addition of starch kept the spatial structure of gluten, and the

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steric hindrance between starch and gluten32 inhibited gluten aggregation due to

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hydrophobic interaction when heated in water, so the exposed cleavage site was more



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than that of gluten. However, due to the attachment of starch on the surface, it was

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possible to partially hide the digestive cleavage sites, resulting in lower digestibility

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than gluten at lower temperatures. With the increase of temperature, the starch was

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completely swelled and fractured, and the spatial structure of gluten was also destroyed

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in the process of breaking down the starch. When the gluten-starch complex was heated

325

to 100°C, the structure was completely broken and became a lamellar structure, which

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is different from the smooth surface of gluten heated alone, due to the presence of starch

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in the heating process. The starch molecules gradually swelled and destroyed the gluten

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surface until complete gelation, increasing the porosity. After heating to 100°C,

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although the starch has completely gelatinized, the high temperature of 100°C directly

330

destroyed the gluten molecules, resulting in a lamellar structure, and the lamellar

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structure exposed more digestive cleavage sites, increasing the digestibility of gluten.

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The intrinsic fluorescence is due to tyrosine and tryptophan in the protein.33 Since the

333

fluorescence of tyrosine and tryptophan is very sensitive to solvent polarity, the

334

emission spectra is strongly influenced by their microenvironment.34 Therefore, the

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intrinsic fluorescence provides valuable information on the structural particularities of

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the proteins in different conditions. To verify whether the addition of starch affects the

337

exposure of digestive cleavage sites, the intrinsic fluorescence of the gluten-starch

338

complex was able to be determined because tyrosine and tryptophan are the cleavage

339

sites of pepsin and chymotrypsin. From the experimental results, the intrinsic

340

fluorescence of the gluten-starch complex was higher than gluten, which illustrated that

341

the heated gluten-starch complex exposed more tyrosine and tryptophan residues during


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the thermal processing. Therefore, the gluten digestion performance in heated gluten-

343

starch was better than heated gluten. The variable trend of intrinsic fluorescence

344

intensity was consistent with the gluten digestibility, which also demonstrated that.

345

In this paper, the effects of starch on gluten digestion during the heating process were

346

studied, and it was found that starch can enhance gluten digestion. When the complex

347

is heated at 100°C, and the proportion of gluten-starch is 1:1, the digestibility of gluten

348

is higher, and more low-molecular weight peptides are produced. The digestion

349

performance is related to the secondary structure variation during the thermal

350

processing caused by hydration increase and disulfide bonds reduction. The gluten-

351

starch-complex spatial structure is looser than gluten after heating, which could expose

352

more protease cleavage sites. The intrinsic fluorescence intensity characterizes the

353

exposure of protease cleavage sites in the gluten-starch complex more than in gluten.

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This study reveals that starch can protect gluten from aggregation due to hydrophobicity

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in the water at lower temperature. While the temperature increases, the starch absorbed

356

in the gluten surface swells, gelatinizes and destroys the gluten surface. In addition, the

357

structure of the gluten is also destroyed by high temperature, which exposes more

358

cleavage sites and enhances gluten digestion.

359

Conflict of interest

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The authors declare no competing financial interest.

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Acknowledgements This work was supported by “The National Key R&D Program of

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China” (No. 2016YFD0401202); and the Special Project of Tianjin Innovation

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Platform (No.17PTGCCX00230).



364

Supporting information

365

The MS spectrum of different samples digestive peptide mapping

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The FT-IR spectra of different samples

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The fluorescence spectra of different samples


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Figure captions

467

Fig. 1 a. The digestibility of different proportions gluten-starch complex and gluten

468

(Blank) b. The digestibility of gluten-starch complex and gluten heated at different

469

temperatures.

470

The different lowercase letters represent significant differences between the data in the

471

same figure (p < 0.05).

472

Fig. 2 The digestive peptide mapping of different proportions of gluten-starch complex

473

and gluten (Blank).

474

In the heat map, red represents compounds with high content, green represents

475

compounds with low content, and the change of color from green to red indicates the

476

increase of content.

477

Fig. 3 The digestive peptide mapping of gluten-starch complex (a) and gluten (b) heated

478

at different temperatures.

479

In the heat map, red represents compounds with high content, green represents

480

compounds with low content, and the change of color from green to red indicates the

481

increase of content.

482

Fig. 4 The secondary structures of different proportions of gluten-starch complex (a).

483

The secondary structures of gluten-starch complex (b) and gluten (c) heated at different

484

temperatures.

485

Fig. 5 The micro structure of gluten-starch complex and gluten heated at different

486

temperatures. (1), (2), (3), (4), (5) are the gluten-starch complex heated at 20℃, 40℃,


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60℃, 80℃, 100℃, and (6), (7), (8), (9), (10) are the gluten heated at 20℃, 40℃, 60℃,

488

80℃, 100℃.

489

Fig. 6 a. The intrinsic fluorescence intensity of different proportions of gluten-starch

490

complex and gluten (Blank) b. The intrinsic fluorescence intensity of gluten-starch

491

complex and gluten heated at different temperatures.

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The different lowercase letters represent significant differences between the data in the

493

same figure (p < 0.05).

494 495



496

497 498 499 500

Fig. 1


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Fig. 2

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Fig. 5


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Fig. 6

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Table of Contents Graphic

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Effects of Starch on the Digestibility of Gluten under Different Thermal

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