The Preparation,physicochemical Properties And Probiotic Activity Of Ginkgo Isomalto Oligosaccharides

Isomalto oligosaccharides are oligosaccharides in which at least one glycosidic bond between glucose residues is an?-1,6 glycosidic bond,and the degree of polymerization is between 2-5.The main components of isomalto oligosaccharides include isomaltose,panose,isomaltotriose,isomalttetraose and isomaltopentaose,which have a wide range of applications in the food processing industry.The main raw material for preparing isomalto oligosaccharides is starch.The source of starch raw materials is mostly food crops,but the shortage of food resources in the world is still serious today.Ginkgo nut is rich in starch and is a good source of woody starch.Therefore,the use of ginkgo starch as a raw material to produce isomalto oligosaccharides,on the one hand,reduces the pressure of insufficient food resources.On the other hand,it also opens up new ways for the utilization of ginkgo resources and improving its economic benefits.In this thesis,the shelled and peeled ginkgo is used as raw material.The ginkgo starch is liquefied,saccharified,and transglycosidized by compound enzymes to produce ginkgo isomalto oligosaccharides.The response surface optimization was carried out for the DE value of the preparation process.The yeast fermentation method was used to separate and purify ginkgo isomalto oligosaccharides.At the same time,the commercially available corn-derived isomaltose was used as a control to measue the physicochemical properties of ginkgo isomalto oligosaccharides and its effect on promoting the proliferation of Lactobacillus plantarum and Bifidobacterium adolescentis.The main findings are as follows:(1)Among the eight ginkgo varieties,the highest amylose content is Dafozhi ginkgo,with an amylose content of 65.6%.Therefore,the Dafozhi ginkgo is used as the raw material to extract starch.The best DE value of ginkgo starch liquefaction is 14%.On the basis of single factor optimization,the optimal liquefaction conditions were obtained through response surface optimization.The p H is 6.0.The temperature is 93.7°C.The starch slurry substrate concentration is 20.9%.The addition of high temperature?-amylase is 21.3 U/g starch and the liquefaction time is 29.4 min.After liquefaction,5 U/g starch of?-amylase and 1 U/g starch of pullulanase were added,and saccharification was performed for 48h.Then the 1.5 U/g starch of?-glucosidase was added for 36h.At this time,the sum of the four functional sugars of panose,isomaltose,isomaltotriose and isomalttetraose is the highest,which is 30.12%.Active dry yeast was used to ferment for 24 hours to reduce the content of metabolizable sugars to refine ginkgo isomalto oligosaccharides.After fermentation,the sum of the four functional sugars reaches 54.00%.(2)Various physical and chemical properties of ginkgo isomalto oligosaccharides were tested,and isomalto oligosaccharides derived from corn were used as a control.The number average molecular weight of the main part of ginkgo isomalto oligosaccharides is 306 D,and the proportion of this part is 93.67%;the phase transition starting temperature of the DSC thermodynamic curve of ginkgo isomalto oligosaccharides is 94.15?,and the phase transition peak temperature T_p is 101.16?,and the termination temperature T_m is 108.14?,which proves that the ginkgo isomalto oligosaccharides has good thermal stability;ginkgo isomalto oligosaccharides solubles in water and insolubles in organic solvents such as ethanol,ethyl acetate,acetone,n-butanol,etc.;the solubility of ginkgo isomalto oligosaccharides can reach 4.31%at 100?and varies with temperature.Ginkgo isomalto oligosaccharides has good hygroscopicity and moisture retention;with addition of Na Cl,its oil absorption has been partially increased;with hydrodynamic analysis,ginkgo isomalto oligosaccharides show the characteristics of a shear thinning pseudoplastic fluid,which belongs to the range of non-Newtonian fluids.Ginkgo isomalto oligosaccharides have a foaming rate of 4.2%and a swelling force of 1.6%;the average particle size of it is 441.0 nm.Under the scanning electron microscope,the ginkgo isomalto oligosaccharides showed a small structured tight network,which was connected by relatively uniform and irregular granules,and the surface of the granules was wrinkled and porous.Ginkgo isomalto oligosaccharides is acid and alkali resistant,and has good stability in the temperature range of 4-70?;it has stronger anti-digestibility than corn isomalto oligosaccharides.In saliva,gastric juice and small intestinal juice,ginkgo isomalto oligosaccharides are hardly decomposed,which proves that it has the basic properties of prebiotics.Ginkgo isomalto oligosaccharides has an inhibitory effect on Streptococcus mutans that causes oral caries,and can be used to replace part of the sucrose and maltose in foods to reduce the occurrence of oral caries.(3)Ginkgo isomalto oligosaccharides have obvious proliferation effects on Lactobacillus plantarum and Bifidobacterium adolescentis.G-IMO-P has the strongest effect on the proliferation of Lactobacillus plantarum and Bifidobacterium adolescentis,followed by G-IMO and C-IMO.When the optimum carbon source concentration of the medium with corn isomalto oligosaccharides C-IMO as the carbon source is 4%,the proliferation effect of Lactobacillus plantarum is the best,and the p H value of the medium reaches the lowest.When the optimal carbon source concentration of the medium with ginkgo isomalto oligosaccharides G-IMO and G-IMO-P as the carbon source is 3%,the proliferation effect of Lactobacillus plantarum is the best,and the p H value of the medium reaches the lowest.When the optimum carbon source concentration of the medium with corn isomalto oligosaccharides C-IMO and ginkgo isomalto oligosaccharides G-IMO as the carbon source is 2%,the proliferation effect of Bifidobacterium adolescentis is the best,and the p H value of the medium reaches the lowest.When the optimal carbon source concentration of the medium with ginkgo isomalto oligosaccharides G-IMO-P as the carbon source is 3%,the proliferation effect of Bifidobacterium adolescentis is the best,and the p H value of the medium reaches the lowest.The change of the p H value of the culture medium and the change structure of the bacterial cell concentration tended to be consistent.Ginkgo isomalto oligosaccharides G-IMO-P can significantly promote the viability of Caco-2 cells,and can inhibit the absorption of glucose by Caco-2 cells and the expression of two glucose transporters SGLT₁ and GLUT₂ m RNA in Caco-2 cells the amount.Therefore,it can be concluded that ginkgo isomalto oligosaccharides has the potential to maintain the stability of postprandial blood sugar.