The Modification Of Yam Starch And Preparation Of Yam Protein Complex

In this paper, firstly, yam starch acetates with different degrees of substitution (DS) were acetylted by the reaction of yam starch with glacial acetic acid/acetic anhydride using sulfuric acid as the catalyst. This study was carried out to understand the changes in physicochemical properties of starch after acetylation. The results showed that the shapes of the yam starch granules were round to oval and most of the starch granules disintegrated with many visible fragments with the increasing DS. The mean particle diameter of starch granule increased ranging from 28.75 to 55.19μm with the increasing DS. The X-ray diffraction (XRD) patterns could be classified as typical of the C-type for yam starch. X-ray diffraction also showed the loss of the ordered C-type starch crystalline structure and the degree of crystallinity of starch decreased from 36.10% to 10.96% with the increasing DS. The thermal analysis results reveal that the starch acetates were more thermally stable than the native starch. The starch acetates showed 50% weight loss at temperatures from 328℃to 372℃while the native starch underwent 50%weight loss at 325℃. The meltage temperature (Tm) of the starch decreased from 273℃to 226℃. And the transition temperature of gelatinization of the yam starch decreased from 65.31℃to 55.13℃with the increasing DS. The native starch showed the higher△Hgel values (14.12 J/g) while the starch acetates showed the lower value (6.059 J/g) with the increasing DS. The RVA parameters suggested that the yam starch show a higher pasting temperature, a higher peak viscosity and a tendency towards high retrogradation, while starch acetates paste showed a lower level of breakdown and setback than the native starch.Moreover, the enzymatic hydrolysis technics of yam starch was optimal, and the morphology and crystallinity properties of enzymatic modified yam starch were also investigated to understand the hydrolysis pattern and mechanism. The optimum liquefaction conditions of yam starch were: the starch concentration 10% liquefaction temperature 90℃,pH6.0,the dose of a-amylase 60U/g and liquefaction time 90 min. The XRD patterns revealed the type of crystallinity of yam starch turn from C to A type after enzymatic hydrolysisFinally, the yam protein complex was prepared and its contents were also analysis. The optimal condition of yam protein complex preparation was as follow: reaction time is 3h and temperature at 50℃, pH=11, using 10 times water to extract. The protein complexes contain 35.2% protein, 25.56% polysaccharide, amino acid 142.52g/kg and several kinds of trace elements.