Physicochemical Properties Of Dioscorea Opposita Thunb. Starch And Resistant Starch

Dioscorea opposita Thunb. not only can decrease blood glucose,but also the function of strengthen the immune system. Therefore, there is a vast range of perspective for exploiting that Dioscorea opposita Thunb. starch widely used in the development of the beverage, the production of degradable films and fat substitutes. With a view to that, This paper mainly studied the physicochemical properties of Dioscorea opposita Thunb. starch and Dioscorea opposita Thunb. resistant starch. Also, deeply research the optimal process of making Dioscorea opposita Thunb. resistant starch through autoclaving and the digestibility of resistant starch. The results of the research are summarized below: 1. Physical and chemical properties of Dioscorea opposita Thunb. starchStarch content of total Dioscorea opposita Thunb. starch was 71.31%. Fat content and protein content was respectively 1.49 and 1.46. Most of Dioscorea opposita Thunb. starch granules were roundness and oval, which the crystalline structure of it was C type. The granules had a clear polarization cross, most of which appeared cross-shaped. Hilum locating at the midpoint, which the granules were around 9-31um in diameter.According to the main outcome measures Dioscorea opposita Thunb. starch paste is with high clarity, retrogradation and gel. Freeze-thaw stability was good that can applied for frozen food. The solubility and swelling power of starch grow as temperature increases.The apparent viscosity of Dioscorea opposita Thunb. starch pastes would decrease as the shearing temperature and shearing time increases. They was in the range of shearing dilution system. The apparent viscosity increase as starch concentration grows. The higher the temperature was, the lower the apparent viscosity of Dioscorea opposita Thunb. starch becomed.Dioscorea opposita Thunb. starch was intense elastic gel, but was soft and high viscosity. It had the property of good heat paste stability but poor cold paste stability. The gelatinization point was high, being from 67.4℃ to 87.8℃, and enthalpy, being 12.53 J/g.2. Autoclave process preparation of Dioscorea opposita Thunb. resistant starchThrough the single factor test, it turned out, in autoclave process preparation, starch content, pH value, pressure heat time, pressure heat temperature and ageing time make a difference on the yield of Dioscorea opposita Thunb. resistant starch. The result of quadratic general rotation design experiment was used to optimize the technological parameters indicated that the influence sequence as followed:starch concentration>pH values> autoclave time.Optimizing the regression model, the optimum of autoclave process preparation for Dioscorea opposita Thunb. resistant starch were obtained:starch content of 25.20%, pH value of 6.26, pressure heat time of 42.85 minutes. On this condition, the yield of Dioscorea opposita Thunb. resistant starch was 25.21%.3. A comparison of physicochemical properties of Dioscorea opposita Thunb. starch and resistant starchDioscorea opposita Thunb. resistant starch exhibited irregular and polygon. X-ray diffraction pattern showed that it had sharp peaks at diffraction 5.59°,15.07°, 17.06° and 21.88°.The maximum absorption wavelength of Dioscorea opposita Thunb. starch was 610nm, and of Dioscorea opposita Thunb. resistant starch was 618 nm. Compared with Dioscorea opposita Thunb. starch, there was no new chemical group, but lack type Ⅰ and Ⅲ absorption band of D-glucopyranose. The solubility and swelling power and water binding capacity increase as temperature grows. The transparency of native starch was higher than resistant starch, but the emulsibility of native starch was lower.The onset temperature, peak temperature, final temperature and enthalpy of transition of resistant starch were higher than native starch. Furthermore, resistant starch had the property of higher heat paste stability and cold paste stability than native starch. According to the result of equation of Herschel-Bulkley showed that both of native starch and resistant starch was the typical pseudoplastic fluid. Meanwhile, comparing with resistant starch, native starch had stronger pseudoplastic and thickening, the easier to shearing dilution.4. The digestibility of Dioscorea opposita Thunb. resistant starchAccording to In-Vitro digest pattern, with digest time growing, the total carbohydrates digestion products of native starch and resistant starch were increased, but the average rate of digestion of native starch and resistant starch were decreased. Futher, the native starch was the most easy to digest. The less RS content,the easier to digest.