| Rice noodle, a kind of stripy or filamentous rice products, has a long history in China. It is classified into fermented rice noodle and non-fermented rice noodle according to different soaking time. Fermentation involved in soaking process plays an important role on the texture and flavor owing to the microorganisms’ activity. However the natural fermentation of rice noodle is hard to-control which may result in poor quality products. The objective of this study was to investigate the change of microorganisms at every processing stages, to determin the critical steps which impact rice noodle safety. To select the dominant strains and study on their metabolic characteristics and function during rice noodle producing. The main contents are as follows:(1) The microbial changes in the process of rice noodle were investigated to determine the critical steps of the microbial index beyond the standard. It was suggested that cooling need pay more attentions as it is the final step after boiling of rice noodle, especially the cooling troughs need to be cleaned and sterilized to avoid microbial contamination. Pathogens were not detected in the production after heating process. It is found that aflatoxin B1in some production samples, it is necessary to control fungi growth in material and production to guarantee the safety of the rice noodle.(2) The culture-dependent and culture-independent methods were combined to study the ecology of microorganisms during the soaking process. It revealed the changes of microorganisms and determined the dominant strains preliminarily. Combining these two approaches, Lactobacillus plantarum, Lactobacillus fermentum, Candida tropicalis, and Bacillus subtilis were found as the predominant microorganisms during the fermentation process.(3) The activities of amylase, protease, and starch degradation of the predominant microorganisms Lb. plantarum, Lb. fermentum, C. tropicalis, and B. subtilis were investigated, and the results were analyzed by SPSS to select the candidates for lab-scale fermentation, the candidates were named L.p-35, L.f-7, C.t-3, B.s-14. Detected the enumeration of these dominant strains in the form of single cultivation and mixed fermentation in rice mash and the production of organic acid. The results showed that Lb. plantarum, C. tropicalis, and B. subtilis could promote the growth of Lb. fermentum, and the content of lactic acid was increased after mixed fermentation.(4) Fermented rice noodles were produced by inoculating L.p-35, L.f-7, C.t-3, and B.s-14. And then the metabolites composition of final products was analysized by1H NMR spectroscopy. The results showed that there were significant differences of metabolites between fortified fermentation groups and natural fermentation group, and these differences also existed in single cultivation and mixed fermentation groups. The contents of low-molecular carbohydrates were greatly increased by inoculating L.p-35+L.f-7+C.t-3+B.s-14. It is kown that the dissolution of low-molecular carbohydrates is beneficial to rice noodle gel quality and growth of lactic acid bacteria. It concluded that the quality of rice noodle could be improved by inoculating L.p-35+L.f-7+C.t-3+B.s-14.(5) L.p-35, L.f-7, C.t-3and B.s-14were inoculated in fermentation process to produce fermented rice noodles. The results indicated that compared with other three fortified groups, the protein content were decreased, starch content and amylose content were increased in fermented rice noodles fortified with four strains L.p-35+L.f-7+C.t-3+B.s-14. The textural qualities and sensory of batch four on elasticity, smooth and smell were better than that of the others. In addition, coliforms and Salmonella were controlled during soaking by inoculating these four strains. |
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