| China is a large producer of starch resources with abundant species.As the rapid development of starch processing technology in recent years,the production of high value-added starch have been widely concerned.The digestibility and retrogradation of starch has been favored by people due to different digestive starch on the needs of different healthy people,and the low retrogradation can extend the shelf life of food.In this paper,corn starch and oat starch were treated with two different forms of amylase respectively.The changes of in vitro digestibility and retrogradation of starch were studied.The physical and chemical indexes were determined and the mechanism of enzymatic hydrolysis was explored.One: The thermostable amylase was transformed by Bacillus subtilis,c?Ltured and purified with the final specific activity is 66.96U/g,the purificative fold of 201.99,the protein molecular weight of 79.1kDa by self-made in aboratory and used to treat corn starch.The digestibility of starch was determined by Englyst method.The content of RDS have increased by 8.96%,SDS decreased by 19.71%,and the RS increased obviously by 10.35%.The gelatinization enthalpy absorption peak decreased from 7.42J/g to 2.43J/g after scanning for 30 days stored at 4?,which indicated that the thermostable amylase could significantly inhibit the retrogradation of corn starch.The content of amylose was reduced from 18.31% to 9.18% and the content of amylopectin was added to 90.82%,determined by Megazyme kit.The content of short chain starch(DP<12)was increased by 13.22% and the content of medium-long-chain starch(13?DP?24)was reduced by 13.22% with the method of HPAEC.The Mw of corn starch treated with amylase was reduced from 6.64×107 g/mol to 2.87×107g/mol.After separating the peak,there are order of magnitude 108 in Peak1 and the 107 in peak2,the effect of thermostable amylase on peak 2 is more obvious.Second,the oat starch was hydrolyzed by commercialized pullulanase which was extracted with weak alkali method in laboratory,the physical and chemical indexes of the starch samples were determined.As a result was determined by Englyst method,the RS content of oat starch increased significantly by 17.83%,and the content of RDS and SDS decreased.The gelatinization enthalpy absorption peak was reduced from 6.11J/g to 2.59 J/g after stored at 4? for 30 days.The amylose content of oat starch was increased by 39.14% and the content of amylopectin was reduced to 50.90% by the method of Megazyme reagent.The amylopectin of small chain(DP<6)was not changed by HPAEC,and the starch in the middle and long chain(6?DP?24)increased by 12.34%,The longer chain(DP?25)starch was reduced from 21.06% to 7.72%,especially for long chain starch(DP?37).The Mw of oat starch decreased from 1.45×108 g/mol to 3.33×106 g/mol,and the Rz decreased,PDI increased significantly.In the determination of static rheology,the data were fitted with Herscehel-Bulkley,showing a significant yield-pseudoplastic fluid,its thixotropic ring area,yield stress ?0,consistency index K was significantly reduced;dynamic rheology The G',G?of the hydrolyzed samples was decreased,indicating that the viscoelasticity was decreased,the viscosity ratio increased and the mobility was enhanced. |
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