| Resistant starch (RS) is defined as the sum of starch and products of starchdegradation not absorbed in the small intestine of healthy individuals. Now, it is a kind ofthe dietary fiber. Recently, researches have proved that RS can not be digested in thesmall intestine, and not supply glucose. However, RS can be fermented in the largeintestine by intestinal microorganisms florae, which produced some short chain fatty acid,such as butyric acid etc. The butyric acid can stimulate the growth rate of the availabilityflorae, and inhibit the growth of cancer cell. All kinds of physiological function about RSare studied both here and aboard. Lots of crystal are produced in the process of preparingthe resistant starch.Why the resistant starch can resist the enzymolysis is ascribe to thecompact structure of crystal. Because of some molecular weight and low water retentionproperty, RS is a suitable material of dietary fiber and processed food.In this study, effects of preparation conditions on the yield of RS of buckwheat werestudied, physico-chemical properties of RS3 were studied by X-ray diffraction apparatus,scanning electron microscope (SEM), Fourier Transformation In fared and Gel PenetrateChromatogram and effects of RS3 on the sensory score and texture properties of steamedbun were primarily discussed. The results were as follows:1. Effects of autoclaved temperature, time, pH value, storage time and concentrationof starch were studied. The yield of RS3 was obviously influenced by autoclavedtemperature and time, and concentration of starch, while influenced by storage time andpH. The relationship of concentration of starch, autoclaved temperature, time and theyield of buckwheat resistant starch was described by a mathematical regression modelbelow: Y=15.8009-0.3541X1+1.1530X2+0.3922X3-0.2200X1X2-00350X1X3-0.0075X2X3-1.9413X12-0.4550X22-1.7434X32The optimum extracting conditions by mathematical simulation were concentrationof starch 59.41％, autoclaved temperature 123.33℃,time 60.79min, when the yield ofthe resistant starch was 16.61％.2. The physico-chemical properties of buckwheat RS3 were studied. Buckwheat starch was proved to be type A crystal mainly by X-ray which differed greatly from thatof RS3 formed in pasting and cooling treatment process, mainly type B or mixture oftype B and V. The RS molecular weight was 13, 550Da(DP=83). SEM indicated thatautoclaved method made the appearance of RS granule different from former buckwheatstarch. It showed that the surface of RS granule exhibited hole and drape, whose shapewas different from that of buckwheat starch, getting together and even inosculated.3. Effects of adding amount of RS3 on the sensory and texture properties of wheatand wheat-buckwheat steamed bun were examined. The results indicated that theaddition of resistant starch would reduce the quality of the steamed bun. It showed thatthe difference of chromatics. The specific volume and springiness decreased with theaddition of RS. The texture properties of steamed bun were affected by the addition ofRS as well as the sensory score. The results showed that the hardness of steamed bunincreased with the addition of RS, while springness decreased. Effects of the addition ofRS on wheat and wheat-buckwheat steamed bun were similar.
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