| RS3-type resistant starch is known as retrograde starch.Nowadays,herb species used for production of commercial RS3-type resistant starch are few and high-purity RS3-type resistant starch products are hardly to be found.Euryale ferox salisb is an annual aquatic herbaceous plant,which produces starchy seeds named euryale ferox.Euryale ferox are edible with high health value,therefore,the development prospects are broad with great market potential.In this research,euryale ferox were selected as raw material for preparation of RS3-type resistant starch with the autoclaving method,debranching-autoclaving method and dual-enzyme method,and the purification of RS was determined.Besides,the physicochemical properties,structure and digestibility in vitro of euryale ferox starch,resistance-enhanced starch and RS3-type resistant starch were characterized,and the effects of euryale ferox resistant starch on the digestibility of rice starch and wheat starch were studied.The main research contents and results are as follows:(1)With the euryale ferox starch(ES)as raw material,the optimum technology of resistance enhancement was determined by single factor experiment and response surface methodology.The results showed that:?The optimum technological conditions of autoclaving method were as follows:starch concentration 12%,autoclave temperature 121 ?,autoclave time 30 min,cooling temperature 4 ?,refrigeration time 15 h,drying temperature 81.5 ?.Following the processing parameters shown above,the content of resistant starch in resistance-enhanced euryale ferox starch was(18.19±0.03)%.?The optimal conditions for preparation of debranching-autoclaving method were as follows:starch concentration 26.5%,pullulanase dosage 4 U/g(dry-base starch),pullulanase response time 2.3 h,autoclave temperature 120 ? and autoclave time 23 min.Following the processing parameters shown above,the content of resistant starch in resistance-enhanced euryale ferox starch was(18.34±0.21)%.? The optimal conditions for preparation of dual-enzyme method were as follows:starch concentration 24.5%,middle-temperature ?-amylase dosage 4 U/g(dry-base starch),middle-temperature a-amylase response time 25 min,pullulanase dosage 4 U/g(dry-base starch)and pullulanase response time 1.5 h.Following the processing parameters shown above,the content of resistant starch in resistance-enhanced euryale ferox starch was(18.23±0.07)%.(2)The optimum purification process of euryale ferox RS3 was obtained by analyzing the influencing factors with three kinds of euryale ferox resistance-enhanced starch.The results showed that:?The order,dosage and conditions of enzyme in purification were pepsin(pH 2.0,temperature 40?,response time 1 h,enzyme dosage 15 U/g(dry-base starch)),low temperature alpha-amylase(pH 6.0,temperature 45?,response time 2 h,enzyme dosage 10 U/g(dry-base starch)),glucoamylase(pH 4.6,temperature 60?,response time 2 h,enzyme dosage was 100 U/g(dry-base starch)).?Detergent:distilled water.?Drying method:freeze-drying.Following the processing parameters shown above,the RS purity of resistant starch was 80%-90%.(3)The gelatinization characteristics,thermal properties,crystal structure,grain surface morphology and molecular groups of starch were analyzed by RVA,DSC,XRD,SEM and FT-IR.The results showed that:? there were significant differences(p<0.05)during three kinds of starches in the structure and physicochemical properties;?The structure and physicochemical properties of euryale ferox resistance-enhanced starch by different methods were different,the dual-enzyme euryale ferox resistant starch showed poor swelling and freeze-thaw stability,and the autoclaving euryale ferox resistant starch was with greater heat stability than others;? The three kinds of euryale ferox RS3 wers porous particles on the surface and belong to B+V type crystals,thus they had high thermal stability and resistance to enzymatic hydrolysis.(4)The in vitro digestibility of euryale ferox starch,resistance-enhanced starch and resistant starch were studied by three-stage and two-stage digestion in vitro.The results showed that:?The digestibility of three kinds of starch samples in oral segment was accounted for 50%to 60%.Among three kinds of euryale ferox resistance-enhanced starch,digestion rate of the dual-enzyme euryale ferox resistant starch was the highest.? Compared with euryale ferox starch and resistance-enhanced starch,the digestion rate and glycemic index of euryale ferox RS were significantly lower(p<0.05).? The digested euryale ferox starch and resistance-enhanced starch had great changes in thermal properties,crystal form,particle morphology and molecular structure,but the structure of digested euryale ferox RS3 had no change compared with before.? three kinds of euryale ferox RS3 have different effects on the in vitro digestibility of rice starch and wheat starch.Above,euryale ferox starch is a good raw material for preparing RS3-type resistant starch.The physicochemical and in vitro digestibility of the starches prepared by different resistance-enhanced technologies were significantly changed due to the changes of the crystal form and structure of starch granules.There was no significant difference in three kinds of euryale ferox resistant starch,however they had different effects on the digestibility of the blends with rice starch and wheat starch respectively.This research provides a certain theoretical basis and practical experience of the materials of RS3-type resistant starch and the production of high-purity RS3-typ resistant starch... |
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