The gel properties and structural changes of sweet potato starch induced by heat-moisture treatment (HMT) were investigated, and its vermicelli textural properties were revealed. HMT increased the relative crystallinity, and the crystallinity reduced with increasing moisture content, which was consistent with the results of DSC. RVA results revealed that the HMT starches showed an increased setback viscosity and a reduced breakdown viscosity, indicating that the HMT starches gel lead a stronger retrogradation tendency. Rheometer results indicated that the HMT starches had a stronger elasticity behavior. The content of amylose of starch and the possible amylose fine molecular change during HMT at different water content were hypothesized, and this caused the gel properties of starch. Consequently, the HMT starch vermicelli exhibited higher hardness, springiness, and chewiness. These mechanistic relations among starch structure, gel properties, and vermicelli quality during HMT will provide useful information for the starch vermicelli industry.
The properties of sweet potato starch and its noodle qualities were investigated on fermentation day 0, 1, 2, 3, respectively, by using Lactobacillus plantarum. The pasting properties, water retention, expansion rate, starch granule and structure, starch noodles qualities (which include broken rate, hardness and extension) were revealed. It was found that the final viscosity and setback of sweet potato starch increased from 268.3 to 294.3 RVU, and 63 to 86.3 RVU, respectively, and the peak temperature increased from 79.25 to 82.5 8C after the first day of fermentation; the peak viscosity and the viscosity breakdown were decreased significantly. Both the water retention and the expansion rate of sweet potato starch increased after fermentation. The crystal structure of the fermented sweet potato starch was destroyed and the starch granule displayed corrosion. The starch noodles qualities for day 1 fermentation were improved significantly, with a decrease in the broken rate and a significant increase in the hardness and extension of the starch noodle.
PRACTICAL APPLICATIONSLactic acid fermentation has been a practiced way to improve nutritional value and taste. Investigation of the changes in rice starch noodles taste has recently been considered. In this work, the degradation of sweet potato starch by Lactobacillus plantarum during fermentation could modify the properties of the starch. Information about these changed physicochemical properties is important to determine the usability of fermented sweet potato starch in various products. So the objective of this study is to study the effect of L. plantarum fermentation on physical properties of sweet potato starch and its noodle qualities, which can be used to develop a feasibility way in improving sweet potato starch noodle quality by lactic acid fermentation.
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