半乳甘露聚糖的酶法降解及理化性质研究

[Objective]Galactomannan is a natural polysaccharide widely distributed in the endosperm of legume seeds.The aim of this study was to investigate the effect of enzymatic degradation on the structure and physicochemical properties of galactomannans,to provide a feasible method for obtaining galactomannans with specific structure and properties,and to broaden their application in the fields of daily chemicals and pharmaceuticals.[Method]Using a mixture of α-D-galactosidase and β-D-mannanase,the effects of variations in different enzyme degradation conditions(substrate concentration,enzymatic temperature,enzyme concentration and enzymatic time)on the molecular weight and monosaccharide composition of galactomannan were investigated.Meanwhile,samples with molecular weights of 1040 kDa,560 kDa,240 kDa,110 kDa,and 60 kDa were selected to evaluate the effects of molecular weight changes of galactomannans on moisture absorption and retention,antioxidant,and α-glucosidase inhibitory abilities by in vitro experiments.[Result]By changing the conditions of enzymatic degradation,the molecular weight of galactomannan undergoes a different degree of decrease.The molecular weight of galactomannan was reduced from 1040 kDa to 60 kDa,at 37°C when the enzyme concentration was 0.15%.Enzymatic digestion altered the ratio of mannose to galactose in galactomannan,with M/G values ranging from a high of 3.01 to a low of 1.78.The reduction of molecular weight significantly improved the biological activity of galactomannan,which showed the highest scavenging rate of 46.88%and 53.36%for DPPH and ABTS free radicals,respectively,when the molecular weight was 110 kDa,and meanwhile,its inhibition rate of α-glucosidase was up to 81.21%,which demonstrated a good biological activity.In addition,galactomannans with different molecular weights showed better moisturizing properties than sodium alginate in dry environments within 2 h.Among them,galactomannan with a molecular weight of 60 kDa maintained good moisture retention(90.26%)for 24 h.[Conclusion](1)Changes in substrate concentration control the degree of enzymatic degradation of galactomannan by affecting the viscosity of the solution;the higher the viscosity of the solution,the less galactomannan is degraded.(2)Enzyme concentration and enzymatic time were the main factors affecting the degradation of galactomannan.By prolonging the enzyme digestion time,α-D-galactosidase removed α-D-galactoside from the main chain,which provided sufficient space and time for β-D-mannanase to fully degrade the mannan main chain,and the M/G value decreased gradually.(3)The antioxidant and α-glucosidase inhibitory activities of enzymatically cleaved galactomannans were concentration-dependent in all molecular weight classes.Moreover,the decrease in molecular weight of galactomannans had a significant gain in improving their antioxidant and antidiabetic activities.(4)More active hydroxyl groups can be exposed through the degradation of galactomannan,increasing the contact area with water molecules,combining with more water molecules to form hydrogen bonds,and improving the ability of moisture absorption and moisturizing.