Preparation Of Slowly Digestible Rice Starch

Slowly digestible starch(SDS) is a kind of modified starch which is paid more attention these years, it is very important for treatment and prevention of several diseases, such as diabetes, moreover it also use in the athletes, in particular long-distance race athlete's carbohydrate addition extender.The rice starch was prepared with neutral protease, papoid and alkaline protease. The alkaline protease showed the best efficiency. The optimum conditions of preparation of rice starch were as follows: rice flour slurry was treated with 1750u/g alkaline protease at pH8.5, 40℃for 12h. The residual protein content of rice starch was 0.91% and the ratio of extraction of starch was 78.58%.Slowly digestible rice starch was prepared by debranching with pullulanase and annealing. The cooked rice starch were debranched with pullulanase followed by cooling and storing to form slowly digestible starch. Cooling quickly and storing at 4℃were helpful to formation of slowly digestible starch; higher enzyme concentration, less debranching time and storing at 4℃for 3d resulted in maximum quantity of SDS. Rice starch debranched with 20PUN/g pullulanase for 4h followed by cooling and storing at 4℃for 3d, the content of the SDS reached to 50.14%. Moisture content of rice starch was adjusted followed by kept at room temperature for equilibration and then heated, the sample were cooled and air-dried at room temperature. Moisture content of rice starch was adjusted to 60% and then heated at 55℃for 12h, the content of the SDS reached to 7.88%. The content of the SDS prepared by annealing was lower than that prepared by debranching with pullulanase.Properties of slowly digestible rice starch debranched and annealed were investigated, including digestibility, granule morphology, crystallographic structure, amylose content, average degree of polymerization, average molecular quantity and gelatinization. The slowly digestible rice starch prepared by debranching, the digestibility reduced, guanule structure disappeared, crystallographic structure changed, A-type disappeared, crystallinity reduced to about 20%, amylose content ranged from 32.15% to 36.98%, average degree of polymerization ranged from 48.80 to 66.75, average molecular quantity ranged from 7905 to 10813, gelatinization temperature reduced by 8.66℃and enthalpy reduced by 17.11J/g of the sample which had 50.14% SDS. Compared to raw starch, the slowly digestible rice starch prepared by annealing, digestibility, granule morphology, crystallographic structure, crystallinity, amylose content, average degree of polymerization, average molecular quantity and gelatinization temperature did not make difference but enthalpy reduced by 15.30J/g.