Highly Branching Modification Of Starch And The Digestion Performance Of Its Products

The slowly digestible starch(SDS),which has both nutritional and physiological functions,has a wide range of applications in food industry.Generally,a series of physical,chemical,and enzymatic methods have been carried out to increase the SDS content of starch.Among these methods,enzymatic modification of starch has many advantages,such as high reaction efficiency and mild reaction conditions,which make it a suitable candidate for the large-scale industrial production of SDS.1,4-α-glucan branching enzyme(GBE,EC 2.4.1.18)can be used in above process,which catalyzes the hydrolysis ofα-1,4-glucosidic linkages and the formation ofα-1,6-glucosidic linkages,leading to a decrease in the starch digestion rate.GBE modification shows the features of simple operation and high productivity,which has great potential for application.In this study,starch was modified with GBE from Geobacillus thermoglucosidans STB02.Starch with different structures was obtained after modification.The effect of structures on digestive performances of starch was studied.The results may provide useful references for the further development of starch with improved slow digestion properties.Firstly,30%(w/v)starch slurries were modified by GBE without gelatinization.Structures of the modified starch were investigated.After GBE modification,the ratio ofα-1,6-glycosidic linkage and the weight-average molecular weight(M_w)of amylopectin increased,the amylose content and the M_w of amylose decreased.Moreover,cyclic polymers were formed.During the modification of tapioca and waxy corn starch slurry,GBE preferred to cleave the chains with DP>25,and reattached the released chains with DP<13.During the modification of corn starch slurry,GBE preferred to cleave the chains with DP>13,and reattached the released chains with DP<13 or DP 25~36.In summary,the short-chain content of modified starch increased,and the long-chain content decreased.Furthermore,the digestion properties of the modified starch were investigated.After treated for 20 h,the SDS and resistant starch(RS)content of modified starch(RC20)were 34.5%and 26.3%,respectively,which was higher than that of control.Secondly,5%(w/v)starch slurries were gelatinized,and then modified with GBE.Structures of the modified product were investigated.After treated for 10 h,theα-1,6-glycosidic linkage ratio and the short-chain(DP<13)content of modified corn starch(GC10)were 69.0%and 11.5%higher than that of control,the amylose content of GC10 was18.1%lower than that of control.The M_w of amylose and amylopectin were both decreased after modification.It could be indicated that GBE tended to cleave theα-1,4-glucosidic linkage of amylose and amylopectin,and reattached short chains during this modification.Furthermore,the digestion properties of the modified product were investigated.After treated for 10 h,the SDS content and RS content of modified corn starch(GC10)were 55.5%and65.0%higher than that of control.Thirdly,20%(w/v)corn starch slurry was modified with GBE in two stage.After treated with GBE for 10 h,the slurry was gelatinized,and then modified again.The structure of two-staged modified starch were investigated.After treated for 20 h,the M_w of amylopectin was 98.9%lower than that of control,67.6%higher than that of the one-staged modified starch(treated for 20 h);the M_w of amylose were 99.8%lower than that of control,58.7%lower than that of the one-staged modified starch(treated for 20 h).Moreover,during two-staged modification,theα-1,6-glycosidic linkage ratio,short-chain(DP<13)content and amylose content were changed considerably,forming the cluster structures.Furthermore,this modification could most significantly decrease the digestion rate of starch.After treated for20 h,the SDS and RS content of modified starch(TC20)were 115.3%and 112.0%higher than that of control.After the injection of modified starch(TC20),the maximum blood glucose concentration was 22.6%lower than that of control.Lastly,the relationship between molecular structures and digestion properties was studied.The SDS content showed positive correlations with the amylose content(r=0.92,p<0.01)or the average external chain length(r=0.94,p<0.01),and negative correlations with theα-1,6-glycosidic linkage ratio(r=-0.90,p<0.01)or the short chains content(DP<13,r=-0.85,p<0.01).Therefore,the cluster structures formed during GBE modification suppressed the digestion rate of starch.