| Starch and polyphenols are common components of plant-based food.In recent years,the interaction between starch and polyphenols has become a research hotspot.It is found that starch and polyphenols can form the starch-polyphenol inclusion complex,which is resistant to digestive enzymes.Thus,this complex is considered as the Type-5 resistant starch.However,its fermentation process was not reported.In addition,the polyphenol structure and amylose content are the key factors which affect formation of the starch-polyphenol inclusion complex.Therefore,debranched rice starch and rice starch and six kinds of polyphenols commonly found in daily diet,including genistein,quercetin,naringin,gallic acid,ferulic acid,and caffeic acid,were used to prepare the starch-polyphenol complexes in this work and the digestibility of the complexes was determined to obtain the highly resistant starch-polyphenol inclusion complex.Moreover,the fermentation process was investigated.The main results were as follows.X-ray diffraction analysis demonstrated that the mixture system of rice starch and polyphenols showed diffraction peaks at 13.0° and 20.0°,and the mixture system of debranched rice starch and polyphenols showed diffraction peaks at 7.5°,13.0° and20.0°.Moreover,the intensity of the diffraction peaks of the mixture system of debranched starch and polyphenols was stronger than that of the mixture system of rice starch and polyphenols.These results indicated that rice starch and debranched rice starch formed V-type inclusion complexes with the six polyphenols mentioned above and the crystallinity of debranched rice starch-polyphenol inclusion complexes was stronger.Differential scanning calorimetry analysis demonstrated that the mixture system of starch and polyphenols exhibited an endothermic peak at 103～117℃,which further confirmed formation of the V-type starch-polyphenol inclusion complex.The polyphenol content in rice starch-polyphenol complexes was in the descending order of the rice starch-caffeic acid complex > the rice starch-genistein complex = the rice starch-naringin complex = the rice starch-gallic acid complex > the rice starch-ferulic acid complex > the rice starch-quercetin complex and the polyphenol content in the debranched rice starch-polyphenol complex was the descending order of the debranched rice starch-genistein complex = the debranched rice starch-naringin complex > the debranched rice starch-ferulic acid complex > the debranched rice starch-gallic acid complex > the debranched rice starch-quercetin complex > the debranched rice starch-caffeic acid complex.In addition,the polyphenol content in debranched rice starch-polyphenol complexes was significantly higher than that in rice starch-polyphenol complexes.In vitro digestion experiments demonstrated that there was no significant difference in the resistant starch content among the six rice starchpolyphenol complexes,while the resistant starch content in debranched rice starchpolyphenol inclusion complexes was the descending order of the debranched rice starch-quercetin complex > the debranched rice starch-genistein complex > the debranched rice starch-ferulic acid complex = the debranched rice starch-caffeic acid complex > the debranched rice starch-naringin complex > the debranched rice starchgallic acid complex.In addition,the resistant starch content of debranched rice starchpolyphenol complexes was significantly higher than that of rice starch-polyphenol complexes,and the resistant starch content of the debranched rice starch-quercetin inclusion complex reached 79.86%.The above results indicated that increasing the amylose content promoted complexation between starch and polyphenols and thus improved the resistance of starch-polyphenol complexes,and the resistance of starchpolyphenol complexes depended on several factors,including the polyphenol content,inhibition of polyphenols on digestive enzymes and the single helix of starch in the starch-polyphenol complex.Subsequently,the six above-mentioned highly resistant debranched rice starchpolyphenol complexes were used to obtain the complex-based resistant starches by in vitro digestion,and the six resistant starches were fermented in vitro.It was found that the debranched rice starch-polyphenol complexes changed from V-type crystallinity to B+V-type crystallinity after digestion.Correspondingly,the complex particles were aggregated into blocks.In addition,all the six complex-based resistant starches were utilized by intestinal flora,and there were no significant differences in gas production,pH value and reducing sugar content among cultures with addition of the six resistant starches.However,fermentation of the debranched rice starch-ferulic acid complexbased resistant starch produced the most acetic acid,propionic acid,butyric acid and total short chain fatty acids during the later fermentation process,which indicated that the debranched rice starch-ferulic acid complex-based resistant starch showed the strongest prebiotic activity.Finally,the fermentation process of debranched rice starch-ferulic acid complexbased resistant starch was compared with that of high amylose corn starch,one kind of Type-2 resistant starch,and high amylose corn starch/ferulic acid mixture.Scanning electron microscopy analysis demonstrated that fermentation damaged high amylose corn starch and the complex-based resistant starch,which indicated that both types of resistant starch were utilized by intestinal flora.During fermentation,the yields of acetate,propionate,butyrate and total short-chain fatty acids were not significantly different between the high amylose corn starch group and the high amylose corn starch/ferulic acid mixture group,while fermentation of the complex-based resistant starch produced the most acetic acid,propionic acid,butyric acid and total short-chain fatty acids,which indicated stronger prebiotic activity of the complex-based resistant starch.The reducing sugar content of the high amylose corn starch/ferulic acid mixture group was significantly higher than that of the high amylose corn starch group,which indicated that the presence of ferulic acid inhibited utilization of resistant starch by intestinal flora.At the phylum level,the presence of the complex-based resistant starch and high amylose maize starch reduced the ratio of Firmicutes to Bacteroidetes,and the ratio of Firmicutes to Bacteroidetes was lowest in the complex-based resistant starch group.In addition,at the genus level,high amylose corn starch/ferulic acid mixture,high amylose corn starch and the complex-based resistant starch significantly promoted the growth of Bacteroidetes,Bifidobacterium,Parabacteria and other beneficial bacteria,which indicated that high amylose corn starch and the complexbased resistant starch changed the composition of intestinal flora to a more beneficial state. |
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