Study On The Properties Of Purple Sweet Potato Resistant Starch And Its Hypoglycemia Mechanism In Type 2 Diabetic Mice

Purple sweet potato(Ipomoea batatas cv.)is an important local economic resource in China,belonging to the Convolvulaceae family.Purple sweet potatoes contain abundant fermentable carbohydrates,with over 40% being naturally resistant starch granules,and amylose starch accounts for 18.5%-33.76% of the genotype starch.During the processing,it is easy to retrograde and generate resistant starch(RS).RS,as a new type of dietary fiber,can participate in the body’s glucose and lipid metabolism in various ways.Research on the relationship between RS,gut microbiota,intestinal metabolites,and hypoglycemic effects has become a hot issue in the fields of food science and modern nutrition.Therefore,this thesis systematically studies the structure,physicochemical properties,and in vitro digestion characteristics of three types of purple sweet potato resistant starch.On this basis,16 S r DNA high-throughput sequencing technology and non-targeted metabonomics technology were used to study the effects of purple sweet potato resistant starch on the gut microbial and intestinal microbial metabolism of type 2 diabetes(T2D)mice,revealing the mechanism of the purple sweet potato resistant starch-mediated hypoglycemic effect of T2 D mice through regulating intestinal flora and metabolism.The research results provide new ideas for personalized and precise nutritional design of purple sweet potato starch and have certain theoretical basis and practical guidance for the high-value processing of purple sweet potatoes and the development and utilization of resistant starch.(1)Study on the structure,physicochemical properties,and in vitro digestion characteristics of type 3 purple sweet potato resistant starchUnder different debranching times(0 h,5 h,10 h,15 h,20 h,and 25h),type 3 purple sweet potato resistant starch(PDA 0 h,PDA 5 h,PDA 10 h,PDA 15 h,PDA 20 h,and PDA 25 h)was prepared using the pullulanase debranching method combined with an autoclave.The structure,physicochemical properties,and in vitro digestion characteristics of PDA were systematically studied.The results showed that purple sweet potato starch was polygonal,circular,and bell-shaped,with a smooth surface,while the surface of type 3 purple sweet potato resistant starch particles was rough,irregular,and had a small molecular weight.The starch crystal changes from a C-type structure to a B-type structure,the crystallinity,and the pasting temperature increases with increased debranching time.As debranching time increased,swelling power decreases,and the weak increase in solubility was observed.At different branching times,compared with purple sweet potato starch,the content of resistant starch in type 3 purple sweet potato increased after 5 to 20 h and decreased after 25 h.This indicates that the combination of the pullulanase debranching method and the autoclave method is a good technology for preparing resistant starch,which can improve the content of resistant starch in purple sweet potatoes to a certain extent.Type 3 purple sweet potato resistant starch forms a moderate glycemic index after 5,10,and 15 h of debranching.The results showed that the PDA 15 h starch obtained by the combination of 15 h of pullulanase debranching time and an autoclave has good anti-digestion properties.(2)Study on the structure,physicochemical properties,and in vitro digestion characteristics of type 4 purple sweet potato resistant starchUnder alkaline conditions,type 4 purple sweet potato resistant starch(CLPSPS-0%,CLPSPS-3%,CLPSPS-6%,CLPSPS-9%,and CLPSPS-12%)was prepared using different amounts of sodium trimetaphosphate(accounting for 0%,3%,6%,and 12% of starch dry weight),and their structure,physicochemical properties,and in vitro degradation characteristics were systematically studied.The results showed that the phosphorus content,cross-linking degree,and degree of substitution of type 4 purple sweet potato resistant starch were improved after modification.The structure of cross-linked starch particles gradually aggregates with each other through adhesion.The crystal type of starch did not change after cross-linking,but with the increase of the cross-linking agent,the crystallinity,swelling index,and peak viscosity of type 4 purple sweet potato resistant starch increased,while solubility and glycemic generation index decreased.Compared with CLPSPS-0%,the addition of a cross-linking agent increased the content of resistant starch(from 66.56%to 83.32%),and the addition of a 12% cross-linking agent formed a low glycemic index(56.98).The results showed that CLPSPS-12%,with the addition of 12% sodium trimetaphosphate,exhibited the best anti-digestion properties.(3)Study on the structure,physicochemical properties,and in vitro digestion characteristics of type 5 purple sweet potato resistant starchAdd lauric acid(accounting for 0%,10%,20%,30%,and 40% of starch dry weight)to gelatinized purple sweet potato starch to prepare type5 purple sweet potato resistant starch(PSPS-LA0%,PSPS-LA10%,PSPSLA20%,PSPS-LA30%,and PSPS-LA40%),and systematically study the structure,physicochemical properties,and in vitro digestion characteristics of type 5 purple sweet potato resistant starch.The results showed that an increase in lauric acid content can improve starch complexing(CI: 33.82%to 58.22%).The surface of type 5 purple sweet potato resistant starch particles is polished in a thin sheet shape;spherical aggregates are embedded in the matrix and have micropores.As the concentration of lauric acid increases,the enthalpy change of the complex decreases significantly,but the enthalpy change increases when the concentration of lauric acid is 40%.The swelling and solubility improve with the increase in lauric acid concentration,the freeze-thaw stability decreases at-20 °C,but increases at 4 °C with the increase in lauric acid concentration.RVA exhibits uneven peak viscosity and the formation of viscous peaks during the cooling stage.In addition,the V-shaped diffraction peak and in vitro hydrolytic enzyme resistance of type 5 purple sweet potato resistant starch were significantly higher than PSPS-LA0%,forming a low glycemic index.Among them,PSPS-LA40% prepared with 40% lauric acid showed the best anti-digestion properties.(4)Study on the effects of purple sweet potato resistant starches on the hypoglycemic activity and gut microbiota in type 2 diabetic miceOn the basis of the research in the first three chapters,PDA 15 h,CLPSPS-12%,and PSPS-LA40% were selected as type 3,type 4,and type5 purple sweet potato resistant starch(RS3,RS4,and RS5)samples to study the hypoglycemic effect of three types of purple sweet potato resistant starch on T2 D mice and the influence of gut microbiota,compare and observe the histopathological characteristics of blood vessels,colon,and liver,determine the diversity and composition of gut microbiota,and construct a correlation heatmap between physiological indicators and dominant gut microbiota.The results showed that compared with the diabetes model mice(MC group),the weight change rate of mice in the positive control group(PC group),purple sweet potato resistant starch group(RS3,RS4,and RS5 groups),and high amylose maize starch group(HAMS group)decreased,and the liver index of mice in the RS3,RS4,and HAMS groups decreased,of which RS3 had the best effect.At the same time,purple sweet potato resistant starch can reduce the content of TG and CHO in the serum of diabetes mice and increase the level of glucosylated serum protein.The histopathological results showed that,compared with the NC(normal control)group,MC group mice suffered from vascular and liver damage.Purple sweet potato resistant starch could increase the thickness of the colonic muscle layer,mucosa,and villus length in varying degrees and improve vascular and liver tissue damage in diabetes mice.RS3 and RS4 had better effects.The results of the intestinal flora showed that purple sweet potato resistant starch could improve the richness and diversity of the gut microbiota in diabetes mice.Compared to the MC group,RS3 promoted the proliferation of Lactobacillus and Bacillus in the mouse intestine and inhibited norank＿f＿Muribaculaceae and Faecalibaculum growth.RS4 and RS5 increased the relative abundance of Bifidobacterium,Faecalibaculum,and Akkermansiacea in the intestine and inhibited the growth of Enterococcus.The correlation heatmap results indicate a positive correlation between blood glucose indicators and Faecalibaculum.Purple sweet potato resistant starch can reduce the blood glucose level of diabetes mice,while RS3 is the best.(5)Study on the effect of purple sweet potato starch on gut metabolites and its hypoglycemic mechanism in type 2 diabetic miceThe effects of purple sweet potato resistant starch(RS3,RS4,and RS5)on intestinal metabolites in T2 D mice were studied using untargeted metabonomics technology.The results showed that compared to the MC group,RS3 group mice had different metabolic pathways,including leishmaniasis,aldosterone-regulated sodium reabsorption,the oxytocin signaling pathway,amoebiasis,and ovarian steroid metabolism;the RS4 group includes lysine degradation,necrosis,and linoleic acid metabolism;and the RS5 group includes choline metabolism,glycerol phospholipid metabolism,bile secretion,steroid hormone biosynthesis,and phospholipid signaling pathways in cancer.The correlation analysis results indicate that cyclohexane,2-hydroxycinnamic acid,dioctyl succinate,and P-chlorophenylalanine are negatively correlated with blood glucose.2-Lysophosphatidylcholine is positively correlated with TG,CHO,and HDL-C,while Bifidobacteria and Facalibaculum are negatively correlated with glucose.RS3,RS4,and RS5 can have a potential impact on the average blood glucose level of T2 D mice,while the regulatory mechanism of different types of purple sweet potato resistant starch is different due to the abundance of the intestinal microbiome and the related pathway of metabolites to blood glucose level.RS3 by adjusting Lachnospiraceae＿UCG-006,Lactobacillus,Bacillus,Aerococcus,Leuconostoc,Weissella,Enterococcus,Lachnospiraceae＿NK4A136＿group,and Klebsiella promote the production of metabolites such as 2,3-dihydro-2-oxo-1H-benzimidazol-1-butyric acid,5-hydroxyindoleacetic acid,N-acetyl-L-glutamic acid,steroid hormones,and glycogen synthetase,and inhibit the production of arachidonic acid and prostaglandins,thus playing a hypoglycemic role in T2 D mice.RS4 regulates Faecalibaculum,Romboutsia,Bifidobacterium,Bacteroides,Alloprevotella,Akkermansia,Desulfovibrio,Candidatus＿Arthromitus,Lachnospiraceae＿UCG-001,and other microbiota genera that promote the production of metabolites such as imidazolium acetate ribose,butyric acid,phosphoenolpyruvate carboxyl kinase,tetrahydrodeoxycortisol,and GABA,while inhibiting α-glucosidase and UDP glucose 6 dehydrogenase are metabolized biologically,which plays a hypoglycemic role in T2 D mice.RS5 promotes metabolites such as glucan 1,4-α-glucosidase,steroids,lecithin,and fecal bile pigment by regulating microbiota genera such as Helicobacter,Bacteroides,norank＿f＿Lachnospiraceae,Muribaculum,Faecalibaculum,and Candidatus＿Arthromitus that inhibited α-glucosidase,glucan 1,6-α-glucosidase,adenine,and other metabolites,which play a hypoglycemic role in T2 D mice.The purple sweet potato resistant starch RS3,RS4,and RS5 can regulate or reduce the blood glucose of T2 D mice by regulating different microbiota to promote or inhibit the production of different intestinal metabolites.