| Type 2 diabetes(diabetes mellitus type 2,T2 DM)is a type of disease in which carbohydrates are not properly utilized that is characterized by increasing blood sugar in the body,damaging toβcells,and insufficient insulin secretion.At the same time,it can cause some complications,such as coronary heart disease,diabetes nephropathy and so on,which causes serious harm to the body.Diabetes drugs can effectively improve the symptoms of diabetes,but they are harmful to body,such as causing intestinal flora disorder,liver function attenuation and so on.In recent years,lactic acid bacteria(LAB)with hypoglycemic function can improve carbohydrate metabolism,symptoms of insulin resistance and oxidative stress in patients with type 2 diabetes.Therefore,resources of LAB with hypoglycemic function are the focus of functional product development.So,in this study,LAB isolated from traditional fermentation foods was used as materials in order to screen strains with hypoglycemic function in vitro,and studied hypoglycemic mechanism and finally selected two strains to ferment goat milk,which provided theoretical and experimental basis for further research and development of new hypoglycemic foods.The main findings were as follows:(1)The inhibitory rate ofα-glucosidase andα-amylase activities were used as the indicators for screening hypoglycemic functional strains.Strain ATCC53103 was the control strain and acarbose was the positive control.Comprehensively comparing the inhibitory rate ofα-glucosidase andα-amylase activities,the results showed that cell-free extracellular supernatants(CFS)of seven strains had high inhibitory rate ofα-glucosidase andα-amylase activities,which were strain Y9-3,PC-2,M9-4,JXM94,GC215,L15 and L31.Furthermore,the inhibitory rate ofα-glucosidase andα-amylase activities of seven strains of cell-free extracts(CFE)were determined.But CFE of Y9-3 and PC-2 had no inhibitory effect on the two kinds of enzymes.Five strains with high inhibitory enzyme activity were selected for subsequent researches,which were strain M9-4,JXM94,GC215,L15 and L31.Through 16S r DNA sequence identification,it could be seen that strain M9-4was Lactobacillus paracasei,strain JXM94 and GC215 were Pediococcus lactis,strain L15was Lactobacillus fermentum,and strain L31 was Lactobacillus mali.(2)The probiotic characteristics of five strains of LAB with high in vitro hypoglycemic capacity were investigated and the results showed that strain L15 had the strongest antioxidant ability.The antioxidant ability of strain L31 and M9-4 were similar,and the antioxidant ability of strain GC215 and JXM94 were relatively weaker.The K-B paper diffusion method was used to analyze the tolerance of five strains to twenty kinds of antibiotics and the results showed that five strains have different resistance of 20 antibiotics.The results of acid resistance experiment,it was found that the survival rate of five strains were lower under p H 2.0 conditions and was higher above p H 2.5 condition.Comprehensive results showed that the survival rate in gastrointestinal fluid of strain GC215,JXM94 and L15 were higher than strain L31 and M9-4.The non-specific and specific adhesion results showed that strain L15 had better intestinal colonization ability than other strain.Based on the results of the in vitro hypoglycemic function and probiotic properties of LAB,Pediococcus lactis JXM94 and Lactobacillus paracasei M9-4 were finally selected for the follow-up study.(3)IR-Hep G2 cells were used as the model to analyze the effects of CFS,CFE and living bacteria suspension on hepatic glucose metabolism and hypoglycemic mechanism.The results showed that the CFS,CFE and living bacteria suspension promoted glucose consumption in normal Hep G2 cells and IR-Hep G2 cells.The CFS,CFE and living bacteria suspension increased the glycogen synthesis and activity of PK in IR-Hep G2 cells,promoted glycogen synthesis and glycolytic reactions,reduced hepatic glucose output and accelerated glucose catabolism.At the same time,they decreased the activity of PEPECK in IR-Hep G2 cells,which impeded the gluconeogenesis process.Besides,samples upregulated the m RNA expression of IRS1,PI3K,GYS2 and AKT genes and downregulated the m RNA expression of GSK3β,PEPCK,FOXO1 and G-6-Pase genes.(4)The effects of functional bacteria on the physicochemical quality,flavor substances and onα-amylase andα-glucosidase activities of goat yogurt were studied by using Pediococcus lactis JXM94 and Lactobacillus paracasei M9-4 single bacteria fermentation and mixed with commercial starter to ferment goat yogurt.The results showed that the addition of functional bacteria significantly improved the inhibitory rate ofα-amylase andα-glucosidase activities of fermentation goat milk,and the inhibitory rate ofα-amylase andα-glucosidase activities were in the range of 39.00%～45.97%and 16.85%～23.74%,respectively.In addition,functional bacteria improved the physicochemical and sensory quality of the product.GC-MS chromatography was used to detect JXM94+LB+ST,M9-4+LB+ST and LB+ST fermentation goat yogurt,which contained 33,35 and 29 kinds of flavor substances,respectively.The addition of functional bacteria increased the variety composition of goat yogurt flavor substances.The storage stability results showed that the p H decreased,the acidity increased,the water holding capacity,viscosity and the inhibitory rate ofα-amylase andα-glucosidase activities of fermentation goat milk decreased during the storage periods.At the end of the storage period,the number of viable bacteria of fermented goat yogurt was maintained at 1×10~7CFU/m L.The inhibitory rate ofα-amylase andα-glucosidase activities of fermentation goat yogurt were in the rage of20.41%～36.67%and 15.07%～18.54%,respectively. |
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