Quality Improvement And Evaluation Of Sweet Potato Starch

Starch noodle is one of the traditional foods in China. It tastes elastic, fine and smooth. Conversion of the cheap and abundance sweet potatoes into sweet potato starch noodles was a practical project.In the research on quality evaluation of starch noodles, two methods of instrumental test and sensory evaluation were used. The significant correlation results indicate that it was practical to use mechanical test instead of sensory test. Shearing stress and the area of strain peak in shearing test could express the hardness of starch noodles, and the elasticity could be represented by springiness index. The standards of good quality sweet potato starch noodle were the pieces of broking noodles≤2, the shearing stress 50-120 g/mm2, the shape distortion 0.2-0.6, the stretching intensity 14 g/mm2, stretching distortion≥0.2.During the production of sweet potato starch noodles, there are many key points to control, such as water concentration, paste concentration , water temperature , keeping temperature during making the starch flours and freezing temperature, aging time, freezing time during the process of refrigeration. The flours are shear thinning fluids. Each flour has an obvious hysteresis loop. Depending on the area of hysteresis loop and on the basis of practice, we can set up the best technical parameters, as 40% water concentration, 4%paste concentration, 50℃water temperature and 50℃keeping temperature. With the method of orthogonality experiment and synthesis rights, the influence of freezing temperature to the quality of noodles is the most evident, aging time second and freezing time the last. The rational freezing technics is as follows: after retrogradation of cooked noodles at 4℃, 6h, froze at -6℃for 8 hours. With SEM, we researched the influence of freezing conditions to the microstructure of noodles.Different raw materials and additives have prodigious influences to the quality of sweet potato starches. In this thesis, physicochemical indexes of Xushu18, Sushu2 and Sushu8, DSC, rheometer were examined. They are significant correlated with the quality of starch noodles. These indexes can be used to control the quality of raw materials and the starch noodles. Alum and sand sagebrush gel are favorable to the retrogradation of starch, as soybean protein isolate restrained to the retrogradation of starch. Sand sagebrush gel is also natural and nontoxic, so it can be used as the additive of noodle starch instead of alum.Some human illness was close with the digestibility of starch. In the experiment of the vitro starch digestibility , the contents of slowly digestible starch (SDS) and resistant starch (RS) were increased as the amylose network formed and stabilized during short-term storage, which showed that the amylose network was largely resistant to amylase. During long-term storage ,the contents of SDS increased .The reason was the recrystallization of amylopectin.