Study On Improving Edible Quality Of Fresh Rice Noodles By Lactobacillus Enhanced Fermentation

Fresh rice noodles have a smooth taste and convenience for processing and consumption,which are favored by many consumers and have a broad market prospect.At present,the production of fresh rice noodles mostly adopts traditional natural fermentation,and the fermentation process mainly relies on experience,which is greatly affected by environmental factors and cannot guarantee the stability of product quality.In addition,the prepared rice noodles by the traditional fermentation process also have disadvantages such as low strength and easy to break,and the product quality also needs to be further improved.Enhanced fermentation of rice by introducing specific microorganisms can effectively improve the defects of natural fermentation and enhance the quality of fresh rice noodles.However,there are limited studies on the enhanced fermentation of fresh rice noodles,especially the understanding of its mechanism of action is not clear enough.Therefore,it is necessary to systematically evaluate the effect of enhanced fermentation on the quality of fresh rice noodles by optimizing the enhanced fermentation process conditions,and deeply explore the relevant mechanism of enhanced fermentation,so as to provide a technical means and theoretical reference for the industrial production of fresh rice noodles.The main contents of this paper are as follows:Firstly,the process conditions of Lactobacillus plantarum STB19 and Lactobacillus fermentum STB11 enhanced fermentation screened from fermented rice noodles were optimized.Taking the hardness,chewiness and cooking loss of rice noodles as indicators,the specific process of Lactobacillus plantarum STB19 enhanced fermentation was determined as the inoculum of 1.0%（v/v）and fermentation at 25°C for 60 h.The process of Lactobacillus fermentum STB11 enhanced fermentation was determined as the inoculum of 1.0%（v/v）and fermented at 30°C for 72 h,and the optimal compound ratio of mixed enhanced fermentation was 2:8.By comprehensively comparing the texture and cooking quality of rice noodles,it was determined that Lactobacillus plantarum STB19 was identified as the best enhanced fermentation strain was used as the research object of subsequent experiments.Secondly,the effects of Lactobacillus plantarum STB19 enhanced fermentation on the quality of fresh rice noodles were systematically evaluated by measuring the texture,cooking and sensory quality of unfermented rice noodles,naturally fermented rice noodles and enhanced fermented rice noodles.The results showed that the enhanced fermentation of Lactobacillus plantarum STB19 significantly improved the texture,cooking and sensory quality of rice noodles.Compared with naturally fermented rice noodles,the hardness of enhanced fermented rice noodles increased by 10.28%,chewiness increased by 6.40%,and adhesiveness decreased by 51.61%,compared with unfermented rice noodles,the cooking loss and breakage rate decreased by 51.72%and 60.02%,respectively,and the total sensory score increased by 54%.Then,the mechanism of enhanced fermentation was studied from three aspects:the gel structure of rice noodles,the physicochemical properties of rice,and the fine structure of rice starch.The results showed that the enhanced fermentation can promoted the formation of a denser gel structure,reduced the protein content of rice,significantly increased the total starch and amylose content,and increased the relative crystallinity of rice,reduced the gelatinization viscosity and initial gelatinization temperature,significantly increased the paste enthalpy.In addition,enhanced fermentation can also reduce the average particle size of rice starch granules,increase the ratio of A chain and B₁ chain,decrease the ratio of B₂ chain and B₃ chain,significantly reduce the average chain length,and reduce the Mw of amylopectin and amylose,the PI value decreased,and the homogeneity of starch molecules was improved.The correlation analysis showed that the average grain size of rice starch and the ratio of A chain,B₁ chain,B₂chain and B₃ chain and the average chain length of rice starch were significantly correlated with the quality of rice noodles,and the smaller the average grain size,the higher the ratio of A chain and B₁chain and the shorter the average chain length,the better the quality of rice noodles,the higher the ratio of B₂ chain and B₃ chain,the worse the quality of rice noodles.In conclusion,the enhanced fermentation of Lactobacillus plantarum STB19 can improved the quality of fresh rice noodles by purifying rice starch and improving its molecular structure.Finally,the effects of enhanced fermentation on the storage quality of fresh rice noodles were investigated by measuring the color,texture quality,cooking quality,water state,crystalline structure and thermodynamic properties during storage.The results showed that the enhanced fermentation of Lactobacillus plantarum STB19 can effectively alleviate the decline of gloss of rice noodles during storage,maintain a better color appearance,slow down the increase of hardness and chewiness caused by the prolongation of storage time,and maintain the cooking loss and breakage rate low,so that the rice noodles can maintain better texture and cooking quality during storage.After 90 d of storage,the hardness and chewiness of enhanced fermented rice noodles increased by 50.36%and 31.86%,respectively,compared with 0 d of storage,which were lower than 53.90%and 48.36%of those of natural fermented rice noodles.,and the breakage rate decreased by 16.95%compared with naturally fermented rice noodles.At the same time,the enhanced fermentation can enhance the water holding capacity of fresh rice noodles,inhibit the release of free water in rice noodles,and slow down the increase of its relative crystallinity and regeneration enthalpy（ΔH）,thereby delaying the long-term aging of fresh rice noodles.