| Resistant starch (RS) is defined as the sum of starch and its degradation that cannot beabsorbed in the small intestine by healthy individuals. Since it was first discovered in1985,related studies on RS by food scientists have never been stopped，the application of RS infood industry has gained more and more attention with various physiological functions havebeen found. Especially when used as a new type of ingredients, RS not only has thephysiological functions of dietary fiber, and has excellent processing characteristics. RS hassignificant importance on weight control and the development on food for special populationsuch as diabetics for its slow digestion rate in vivo,which can suppress glycemic index (GI)rising rapidly. Recent years, studies on the preparation of resistant starch have beendeveloping rapidly. As a major power of starch resources in our country, the annualproduction of corn starch reaches to2million tons. Therefore, related studies on thepreparation of corn resistant starch by normal corn starch have significant importance onpromoting the reasonable development and utilization of resources.In this study, normal corn starch was adopted as material and the resistant starch contentin the samples were adopted as the main indicator to explore the effect of various factors onthe resistant starch formation by autoclaving treatment and enzymatic processing. In order toimprove the yield of RS, the optimal parameters for the preparation of resistant starch wereinvestigated by orthogonal test and CCD. For making a preliminary assessment of its value onthe application in food industry, some physical and chemical properties of the samples werealso analyzed. The main conclusions were as followings:Starch concentration, retrogradation time and autoclaving time has significant effect onthe formation of resistant starch in the preparation of RS by autoclaving treatment method.Moreover, the effects of starch concentration and autoclaving time on RS formation were atextremely significant level; the effect of retrogradation time was also at significant level, thesubsequence of effecting was starch concentration> autoclaving time>retrogradation time.The optimal preparation parameters of RS were as follows:30%of starch concentration,30min of autoclaving time,16h of retrogradation time, and the content of prepared RS reachedto4.58±0.08%, almost increased by3times compared to the original maize starch. Moreover,physical properties of the samples obtained by autoclaving also changed compared withoriginal corn starch: the SA and SP index declined and with the increase of resistant starch content, the solubility, swelling degree and transparency was reduced.In present study of preparation of corn resistant starch by pullulan enzymatic treatment,the influence of pullulanase amount, enzyme reaction time, storage time and storagetemperature on maize resistant starch yield were investigated, results showed that the impactof various factors investigated in this study on RS yield were significant.The levels of theseparameters were also optimized by using response surface methodology to enhance the RSyield. After optimization the regression model was obtained:RS%=7.248+0.138X0.065X+0.070X0.008X20.001X212313+0.005X1X2The regression model was highly significant and can describe the relationship between RSyield and the3factors adequately. The optimal preparation conditions of RS were asfollowings: pullulanase additive amount20U/g starch, enzyme reaction time24h, storagetime36h and storage temperature4℃. Treated under these conditions the RS content insamples reached to9.75±0.20%,increased by89.4%compared to the original maizestarch,and also much higher than the samples treated by autoclaving which indicates thatdebranched by pullulanase can obiviously improve the final RS content.Scanning electronmicrographs showed the raw maize starch granule morphological features were damaged andthe RS samples had more irregular shapes and without granular structure and samples withdifferent RS content also showed different granule morphological features. The amylosecontent of each sample changed as the pullulanase adding amount changed and results showedthe highest amylose content was41.23%when the pullulanase adding amount reached to15U/g. Compared with the native starch, the transparency of all samples reduced afterenzymatic treatment and with the increasing of RS content, transparency was also reduced.The gelatinization character of corn resistant starch were determined with Rapid ViscoAnalyser（RVA）,results showed that all the parameters are decreased,which indicates the RSsamples had poor processing property so more work is need to be done to improve the pasteproperties of corn RS sample to improve their applicable properties.In the study of preparation of corn resistant starch by pullulanase combined withthermo-stable α-amylase method, the influence of α-amylase adding amount, reaction time ofα-amylase, pullulanase adding amount and starch concentration on the resistant starch yieldwere investigated. Results showed that impact of the factors investigated in this study on RSyield were significant and for enhancing the RS yield, levels of these parameters were alsooptimized by using response surface methodology. After optimization the regression modelwas obtained:RS%=-5.434+4.624X1+0.225X2+0.322X3+0.530X4-0.808X12-0.009X22-0.005X32-0.028X42The regression model was highly significant and can describe the relationship between RS yield and the4factors investigated adequately. The optimal preparation conditions of RS wereas followings: α-amylase adding amount3U/g, α-amylase reaction time35min, starchconcentration25%and pullulanase adding amount10U/g, treated under these conditions theRS content in samples reached to10.78±0.54%, much higher than the samples treated onlyby pullulanas which indicates that debranched by pullulanase can obiviously improve the finalRS content.Results also indicated that the thermal α-amylase had a significant effect on thepolymerization degree（DP）of starch molecules,and DP of the samples showed an obviousdownward trend as the α-amylase adding amount increased.As the polymerization degree ofstarch molecular had a significant effect on the RS yield,so it was important to take measuresto control the DP in a certain range. The RS content of samples treated by α-amylasecombined with pullulanase improved signicantly compared to that treated only bypullulanase,which indicates that when the original corn starch was enzymatic hydrolyzed byα-amylase and then debranched by pullulanase,the final RS content may obtain a notableimprovement.Results of SEM showed that,the raw maize starch granule morphologicalfeatures were damaged and the RS samples had more irregular shapes and without granularstructure and the broken starch granules content increased as the α-amylase adding amountincreased.The differential scanning calorimeter pattern showed that compared with theoriginal corn starch,the temperatures of the onset, peak, conclusion and enthalpy ofgelatinization were increased.The RS samples exhibited an endothermic transition at100℃~140℃in the DSC thermogram which apparently was due to the melting of recrystallizedamylase,and the parameters increased as the RS content increased,which indicates that theresistant starch with an outstanding thermal stability. |
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