Preparation And Fractionation Of Spring Dextrin And Its Application In Bread

Spring dextrin(SD)refers to linear dextrins in which the glucose units are linked by ?-1,4 glycosidic bond and have a helical flexible conformation of the amphiphilic polysaccharide polymer,and the specific degree of polymerization of SD has shown excellent properties in inhibiting amylopectin and amylose aging?The property of SD differs due to the different degree of polymerization,and SD has the characteristics of polydispersity.In this paper,the SD was prepared by anhydrous ethanol,and SD was obtained with different relative molecular weight.The effects of different relative molecular weights on the dough characteristics,bread baking characteristics and bread aging properties were also studied.SD was prepared by enzymatic hydrolysis of waxy maize starch with pullulanase alone,and the process parameters were optimized by one-factor-at-a-time method and response surface methodology.The optimal results were observed at conditions of enzyme dosage 420 U·g-1starch,hydrolysis for 6 h at 53.3?,pH 5.0,predicted using mathematical predictive model.Under these conditions,SD purity was 99.2%.The chain-length distribution of SD was also evaluated.Results showed that the proportion of SD with DP<60 were 95.5%,and the relative contents of SD with DP6~12,DP13~24,DP25~36 and DP37~60 were 24.40%,45.08%,19.60% and 10.92%,respectively.SD-F20,SD-F40,SD-F50,SD-F60 and SD-80 were obtained by fractional precipitation of SD with different concentrations of ethanol.Multi-angle laser gel chromatography(HPSEC-MALLS-RI)and high precision spectrophotometer were used to determine the relative molecular weight and chromaticity.Compared with the unrated SD(SD-Y),the relative molecular weight distribution of precipitated components became narrower.With the increase of ethanol concentration,the relative molecular weight of each component decreased.The relative molecular weight gaps between SD-F20 and the other four fractions are large,so the five precipitation fractions were classified to HMW-SD and LMW-SD.Effects of HMW-SD and LMW-SD addition on the dough properties were analyzed by rapid viscosity analyzer(RVA),farinograph and extensograph instruments.The results showed that both HMW-SD and LMW-SD had no significant effect on flour pasting temperature,and could decrease the peak viscosity,valley viscosity,final viscosity,recovery value and disintegration value of flour.Along with increasing two kinds of SD addition,the water absorption and formation time of dough increased,and the degree of weakening decreased.When the addition of HMW-SD and LMW-SD was 3.0%,dough stability time reached the maximum,21.2 and 19.8 min,respectively.The stretch curve area and resistance to extension of the dough was larger than that of the control group with SD addition of 1%~2%.Two kinds of SD had no significant effect on dough extensibility with addition of 1%~2%.Effects of SD on baking performance of bread was analyzed by measuring specific volume,baking loss rate,color,texture profile,cell structure and sensory evaluation of bread.The results indicated that SD could increase the specific volume,reduce the baking loss rate,with effect of LMW-SD better than that of HMW-SD.HMW-SD could brighten the color of bread crumb and LMW-SD had no obvious effect.SD of appropriate amount improved texture profile and bread cell structure with no obvious difference between HMW-SD and LMW-SD.Overall acceptability of bread reached maximum,with high relative molecular weight SD and low relative molecular weight SD addition of 2%.Effects of SD on the changes of firmness,moisture migration and retrogradation of amylopectin of breads during storage were investigated.The results showed that LMW-SD could decrease bread hardening rate constant k and hardness final value F7,reduce rate of bread moisture migration and delay regeneration of amylopectin.HMW-SD could increase the bread hardening rate constant k and hardness final value F7,speed up the regeneration of amylopectin.