| Alginate is a kind of soluble dietary fiber(SDF)and widely exists in seaweed,which was reported for their antibacterial,antidiabetic,anti-obesity and antitumor physiological properties.However,alginate as a biomacromolecule due to its strong hydrophilic and gelation produce extremely high viscosity in aqueous solution even at a low concentration.When alginate was incorporated with food at a physiological effective concentration,it will form an extremely high viscous solution and poor palatability,thus restrict alginate as a nutrition supplementary applied in food system.Therefore,producing low molecular alginate is conducive to promoting the application of alginate as a dietary fiber supplement.In this study,alginate lyase(ALyase)from Vibrio natriegens SK42.001 and cellulase from Aspergillus niger were used to degrade alginate in different ways,and the reaction conditions of different molecular weight fractions were obtained.The molecular weight parameters,chemical structure and chain conformation were characterized.And physiological activity of each fraction was studied.Firstly,the changes of molecular weight parameters of partially degraded alginates(PDA)with Alyase and cellulase were studied by HPSEC-MALLS-RI.One-step and step-by-step methods were used in degradation process.The chain scission models and the degradation conditions of low molecular weight products determined.The results showed cellulase was useless on alginate alone.Alyase showed multiple scission model and central scission model,and step-by-step method improved the utilization rate of Alyase.The degradation conditions of Alyase:one-step and step-by-step degradation were controlled within 2 h and 5 h respectively,and the enzyme amount was 2.56-10.24 U/g.The synergistic effect of Alyase with cellulase was further explored by step-by-step method.The interval addition times were studied at 0 min(iACS),30 min(iACM),60 min(iACE).The results showed Alyase prefer to molecular weight(M_w)?10~5 g/mol,cellulase prefer to 10~4-10~5 g/mol.The PDI values were stable and approached to 2 infinitely in the iACE method,showing a random scission model.In the iACS and iACM methods,the molecular weight components of the products increased,and PDI value increased to 5.14 and 7.02 respectively.Secondly,four PDA were obtained with different enzyme activities(2.56,5.12,7.68,10.24U/g).Four PDA samples were defined as PDA1,PDA2,PDA3 and PDA4 and the absolute molecular weight were 10.48×10~4 g/mol,6.75×10~4 g/mol,4.81×10~4 g/mol and 3.99×10~4 g/mol.The PDI increased from 1.7 to 2.3(<10).The?-D-mannuronate/?-L-guluronate(M/G)ratio increased from 0.8 to 1.8.~1H NMR analysis showed ALyase preferred to G-block.The intrinsic viscosity decreased from 170.9 mL/g to 38.914 mL/g.Analysis of AFM and Huggins theory confirmed PDA1 and PDA2 form a random coil conformation in solution,PDA3 and PDA4formed a spheritic random coil in solution.Finally,the physiological properties of PDA were studied in vitro.Within the glucose concentration of 5-200 mmol/L,the adsorption capacity of PDA3 and PDA4 was higher than that of ALG.PDA4 and ALG were all showed a liner relationship with glucose concentration with slope of 2.3 and 1.4 respectively.While the adsorption capability of PDA1 and PDA2lower than that of ALG.PDA retarded amount of glucose diffusion.Specifically,the retarded amount of glucose diffusion of 5%PDA2 and PDA4 were 28%-34%and 31%-44%,which were higher than that of ALG(22%-27%).PDA inhibited the activity of?-amylase significantly(P<0.05).3%PDA inhibited the activity of glucoamylase(P<0.05).The static rheological properties showed that PDA were shear thinning swelling plastic fluids.The dynamic rheological properties showed that the addition of PDA in corn starch increased the elasticity and reduced the viscosity of the mixed system,and improved the rheological properties of food system.In a word,the study indicates that PDA have potential application value as dietary fiber supplement. |
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