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Elucidation of Fermentation Effect on Rice Noodles Using Combined Dynamic Viscoelasticity and Thermal Analyses

¹College of Food Science and Nutritional Engineering, China Agricultural University, PO Box 40, Beijing 100083, China. ²Food Physics Laboratory, National Food Research Institute, 2-1-12 Kannondai, Tsukuba, Ibaraki 305-8642, Japan. ³Present address: Department of Physics, Chuo University, 1-13-27, Kasuga, Bunkyo-ku, Tokyo 112-8551, Japan. ⁴Corresponding author. E-mail: kaoruk@affrc.go.jp

Natural fermentation of whole polished rice grains (indica) is a traditional processing method widely applied in China and South Asia to improve the texture of rice noodles. To elucidate the effects of fermentation on noodle texture, thermal analysis of rice flour and rheological measurement were performed on a gel made from the rice flour with the same solids concentration as practical noodles. The test method proved useful for monitoring starch granule swelling, gel forming, and retrogradation of rice gels during rice noodle production. Dynamic viscoelasticity in a temperature ramp sweep test showed that starch granules of the fermented sample swelled more and were more resistant to breakdown than those of the nonfermented sample. Differential scanning calorimetry revealed that the gelatinization temperature of fermented rice flour shifted to a lower temperature. The decreased protein content after fermentation also played a role in the modified rheological and thermal properties of fermented rice flour. Both fermented and nonfermented rice flour formed an elastic gel just after heating to the conclusion temperature of gelatinization (T_c). The fermented rice flour gel formed earlier with a well-formed structure; however, it had slower retrogradation during aging. The result also indicated that the retrogradation of amylopectin impaired the desired texture of rice noodles.