| Resistant starch(RS)has irreplaceable advantages in maintaining blood glucose homeostasis,controlling body weight,and promoting gastrointestinal health.At present,RS is a newly developed food ingredient in China,and there are still some problems such as low active component content and poor heat resistance during the preparation process of RS.At the same time,RS,as a kind of carbohydrate,is often involved in the complex gastrointestinal and digestive system.It is crucial to understand the complex transformation process and its anti-digestion mechanism of RS in the digestive process for its physiological function of intestinal health.However,there are few studies on this aspect,especially lack of study on the dynamic changes of RS along the oral-gastrointestinal tract.Based on this,this study took recrystallized resistant starch(RS3)as the research object,explored the preparation process of RS3 with high RS content and heat resistance.Finally,human fecal microflora and healthy mice were used to explore the fermentation process of RS3 and its effects on the intestinal flora,providing theoretical basis for RS utilization in the future and promoting the functionalization and industrialization development of RS.Recrystallized resistant starch(RS3a)was prepared using ultrasound assisted annealing(ANN)treatment of fractionated debranched starch(DBS)from waxy maize starch.The effects of fractionation,ultrasound,and ANN treatment on the structures and digestibility of RS3a were investigated.The study found that the total ratio of B1 chain and B2 chain of fractionated DBS was as high as 71.1%,indicating that the chain length of fractionated DBS was relatively ordered and fractionated DBS was easy to recrystallize.The ultrasound and ANN treatment increased the relative crystallinity from 31.9%to 78.1%,and retrograded enthalpy changes((35)H)from 9.4 to 25.2 J/g,of RS3a.In addition,RS content of RS3a reached 65.4%,and its digestibility coefficient decreased from 1.3E-02 to 2.7E-03 min-1,indicating that the fractionation of alcohol precipitation combined with ultrasound assisted ANN treatment technology significantly improved resistance to enzymatic hydrolysis of RS3a.Furthermore,heat-resistant recrystallization resistant starch(RS3b)was prepared by low-temperature recrystallization and heat-moisture treatment(HMT)technology of fractionated DBS.The effects of fractionation combined with low temperature recrystallization and HMT on the formation of RS3b were investigated in this study.According to research findings,the relative crystallinity of RS3b increased from 27.6%to 75.1%,and the peak gelatinization temperature of RS3b was up to 115.4°C.At the same time,the RS content of RS3b was up to86.7%.In addition,after cooking at 100°C for 30 min,the RS content of RS3b was still about36.5%,while RS content of the control sample initial DBS was only 17.2%.The results showed that the RS content and thermal stability of RS3b were significantly improved by fractionation combined with low temperature recrystallization and HMT.A simulated oral-gastric-intestinal digestion system was constructed to systematically study the changes of fine structure,thermal properties,and particle morphological characteristics of the digestive products of RS3 groups RS3a,RS3b,and control groups high amylose corn starch(RS2),esterified starch(RS4),starch-lipid complex(RS5)in oral,stomach,and small intestine,and then their digestive degradation process was revealed.The short chains of RS3a and RS3b were easily digested and the starch long chains were hydrolyzed into the appropriate starch chain length(B1 and B2 chains),thus obtaining a more stable structure resistant to enzymatic hydrolysis during their digestion process.The X-ray diffraction peak intensity of RS3a digestive residue in oral phase decreased and increased significantly in small intestine phase,while the diffraction peak intensity of RS3b digestive residue showed an increasing trend with digestive processing from mouth to stomach to small intestine.The diffraction peaks of RS3a and RS3b after intestinal digestion were the shartest,indicating that the starch amorphous area was hydrolyzed first,followed by the irregular accumulated crystals,and finally the digestive residues with relatively uniform crystal structure were obtained in the digestion process.The(35)H of digestive residue of RS3b increased to 20.2 J/g after hydrolysis at the mouth,stomach,and small intestine,further proving that starch amorphous region was hydrolyzed,the proportion of crystalline structure increased,and the double helix content relatively increased.The particle structure of RS3a and RS3b digestive residue was still relatively dense and uniform except that many small nanoparticles were added on their particle surface.The effects of RS3 groups RS3a,RS3b,and control groups RS2,RS4,RS5 on the yield of short chain fatty acid(SCFA)and the growth of beneficial bacteria in intestinal tract were investigated by simulating the intestinal environment with fresh fecal extracts of healthy adults and using the digestive residues treated with simulated oral-gastrointestinal solution as fermentation substrate.According to research findings,the total SCFA yield of RS3a and RS3b was much higher than that of control groups.RS3a had the best effect in promoting the production of acetic acid and valeric acid,and RS3b had the best effect in promoting the production of propionic acid and butyric acid.In addition,both RS3a and RS3b could promote the proliferation of Bifidobacterium in the early fermentation period.However,the proliferation effect of RS3a and RS3b on Bifidobacterium in the later fermentation period was not as good as that of the control groups RS2 and RS4.Meanwhile,RS3a had the most significant effect on the growth of Lactobacillus in the whole fermentation process,while the RS3b and control groups RS2,RS5 had obvious effect on the proliferation of Lactobacillus only in the late fermentation period.The fine structure and properties of obtained digestive products of RS3 groups RS3a,RS3b,and control groups RS2,RS4,RS5 in the stomach,duodenum,and ileum of mice were systematically analyzed by using the anatomical technique of extraction products from gastrointestinal tract,and their in vivo digestive degradation process was further revealed.The study found that RS3a and RS3b could significantly reduce the release level of blood glucose.During in vivo digestion process the proportion of ultra-short chain and A chain of RS3a and RS3b digestive residue gradually increased,the proportion of B1 and B2 chain gradually reduced,and B3+chain proportion was not too obvious changes.The final digestive residues in the ileum(RS3a-I90 and RS3b-I90)could still maintain a high proportion of suitable chain length,accounting for more than 60%.After oral gavage for 30 min,the part of the starch crystalline structure of gastric digestion residue of RS3a and RS3b was acidized.After oral gavage for 60 min,the crystalline structure order of duodenal digestion residue of RS3a(RS3a-D60)increased,while the crystalline structure of duodenal digestion residue of RS3b was more orderly than that of RS3a-D60.After oral gavage for 90 min,the crystalline structure of RS3a-I90 was weakened,indicating that the partial crystal structure had been hydrolyzed.And RS3b-I90 still maintained an orderly crystalline structure,indicating that RS3b was more resistant to enzymatic hydrolysis than RS3a.As a whole,the final digestive residues obtained from in vivo digestion process of RS3a and RS3b could retain stable structures,and then reach the cecum and colon for fermentation and utilization.Finally,in vivo animal experiments were conducted to investigate the effects of RS3 group RS3a,RS3b,and control groups RS2,RS4,RS5 on the basic growth index,metabolites,and intestinal flora composition of mice.It was found that RS could maintain the normal growth of mice and effectively control the weight gain of mice.Meanwhile,RS3a and RS3b significantly improved fecal water content,especially the feces of RS3a group mice were particularly fluffy.RS3a significantly increased the concentrations of acetic acid,propionic acid,and butyric acid,while RS3b group and control groups had less obvious promoting effect.In addition,RS3a significantly interfered with the?-diversity index of intestinal microbiota,and significantly reduced the richness and diversity of intestinal microbiota.At the same time,RS3a reduced the ratio of abundance of Firmicutes and Bacteroidetes,which further confirmed the benefits of RS3a in gastrointestinal health. |
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