| As a characteristic food in Yunnan,fresh rice noodles are deeply loved by consumers because of their nutrition,convenience and smooth taste,but due to the high moisture content of fresh rice noodles,the production process is more cumbersome,and the sanitary conditions of small workshops are poor,so that the quality of the products is different and easy to be contaminated by microorganisms.At the same time,there are problems such as adhesion and starch aging during storage,resulting in shortened shelf life and reduced food quality.In this study,rice(Yun Indica No.8 and Yun Indica No.4)from Qiubei County,Yunnan Province were used as raw materials,and the processing technology of fresh rice noodles was optimized by the experimental design of response surface,and the additives-free fresh rice noodles were made with the best process parameters.Taking the homemade fresh rice noodles as the research object,the quality change law and the correlation between its indicators in the storage process were studied,the key factors of quality deterioration were determined,and the microbial flora changes in the quality deterioration rice noodles under different storage temperatures were explored.At the same time,the influence of physical and biological preservation measures on the quality change of fresh rice noodles was explored,and the optimal composite sterilization and preservation process was determined.The main research contents and results are as follows:(1)The amylose content of Yunxian 8 rice and Yunxian 4 rice was 27.97%and 25.64%,respectively.The processing conditions of fresh rice noodles were optimized by using single factor and response surface tests,and the optimal process parameters were determined by sensory score and moisture content:raw material ratio of 7:3 g/g,cooking time of 2.47 min,and cooking temperature of 88.9℃.(2)The quality deterioration of fresh rice noodles under different storage conditions was studied.The results showed that the sensory score,brightness value(L~*)and water absorption rate decreased significantly during storage at 37°C.The moisture content,hardness,elasticity and chewiness increased first and then decreased.The acidity,cooking loss,viscosity andα-amylase activity increased significantly.After surface sterilization treatment,the total number of colonies during storage was less than that without sterilization.The change trend during storage at 25°C was consistent with that at 37°C.However,during storage at 4°C,the sensory score and moisture content decreased gradually,the acidity increased slightly,the L~*value decreased slightly,the water absorption rate increased first and then decreased,the cooking loss increased gradually,the hardness,elasticity and chewiness showed an overall upward trend,the viscosity showed a downward trend,the activity ofα-amylase was basically unchanged,and the microorganisms gradually increased after 1 day of storage.At the same storage temperature(37°C,25°C and 4°C),the total number of colonies in large packaging and small packaging fresh rice noodles showed the same trend.At 37℃,the microbial indexes were significantly or very negatively correlated with the changes in sensory quality and water absorption,and significantly or very positively correlated with the changes in acidity.At 25℃,the microbial indexes were significantly or very negatively correlated with the changes of sensory quality,water absorption and viscosity,and positively correlated with the changes in acidity.At 4℃microbial indexes were significantly or very negatively correlated with changes in sensory quality,moisture content and color,and significantly or very positively correlated with changes in acidity and cooking loss(P<0.05 or P<0.01),indicating that microbial indexes could be used as key factors to evaluate the deterioration of storage quality of fresh rice noodles.(3)The analysis of 16S r RNA microbial diversity showed that there were differences in the dominant bacterial communities in the quality deterioration rice noodles at different storage temperatures.At the phylum level,Proteobacteria and Cyanobacteria are used as the dominant phylum.At the genus level,the relative abundance of Pseudomonas,Allorhizobium Neorhizobium Pararhizobium Rhizobium and Pantoea increased significantly after storage at 37℃for 3 days;After storage at 25℃for 3 days,the relative abundance of Pseudomonas and Aeromonas increased significantly.After storage at 4℃for 7 days,the relative abundance of Pseudomonas and Acinetobacter increased significantly(P<0.05).(4)The analysis of ITS fungal diversity showed that there were differences in the dominant fungal communities in the rice noodles with poor quality at different storage temperatures.At the phylum level,Ascomycota is the dominant phylum for all samples.At the genus level,the relative abundance of Schizophyllum and Neofusicoccum increased significantly after storage at 37℃for 3 days;After storage at 25℃for 3 days,the relative abundance of Botrytis and Cladosporium increased significantly.After storage at 4℃for 7days,the relative abundance of Penicillium and Epicoccum increased significantly(P<0.05).(5)Three kinds of packaging materials,CPP/PA cooking bag,PET/AL/PA/RCPP cooking bag and glass bottle with metal screw cap,were selected to study the influence of different packaging materials on the storage quality of fresh rice noodles.The results show that the packaging of glass bottles with metal threaded caps can slow down the moisture content reduction rate,slow down the change rate of hardness,elasticity and chewiness,slow down the growth and reproduction of microorganisms,and slightly extend the shelf life of fresh rice noodles during storage,which can be used as a candidate packaging container for fresh rice noodles.(6)Thermal sterilization can make fresh rice noodles shelf life at 37°C for up to 8 days,but after sterilization,the cooking quality decreases,the sensory score decreases.Microwave sterilization can keep the fresh rice noodles for up to 3 days,and has a great influence on sensory score,cooking loss,breaking rate and texture characteristics after sterilization.Considering the indexes,the optimal thermal sterilization conditions were selected as temperature 90℃and sterilization time of 30 min.The optimal microwave sterilization conditions are power 490 W and sterilization time of 60 s.(7)Before sterilization,spraying edible oil on the surface of fresh rice noodles has an effect on improving the adhesion phenomenon.Under the premise of ensuring the sensory quality and texture of the product,when the spraying amount of olive oil is controlled to 7%,the spraying amount of sesame oil is controlled to 3～5%,and the spraying amount of Meitan fruit oil is controlled to 5%,the anti-adhesion effect is good,the sensory score of fresh rice noodles is high,and the cooking loss and breaking rate are low.Among the three edible oils,olive oil has the best anti-adhesion effect on fresh rice noodles.(8)Both nisin and tea polyphenols effectively inhibited the growth of microorganisms during the storage of fresh rice noodles,and the inhibitory effect gradually increased with the increase of addition amount.When the addition amount of nisin was 0.03 g and above,the fresh rice noodles could be kept for 9 days at 37°C,and the sensory score was higher and the edible quality was better.Compared with nisin,when the addition amount of tea polyphenols was 0.04 g,the fresh rice noodles could be kept for 10 days at 37°C,but it had a great influence on the sensory quality of fresh rice noodles.The higher the addition amount of tea polyphenols,the lower the color,shape and taste scores in the sensory of fresh rice noodles,and the worse the edible quality.In summary,the parameters of the best compound sterilization and preservation process of fresh rice noodles are:nisin 0.03 g,olive oil spraying amount 7%,packaging material selection glass bottle with metal threaded cap,thermal sterilization temperature 90°C,time30 min.Under this sterilization process,fresh rice noodles can be kept at 37℃for 9 days,and the fresh rice noodles have uniform color,glossy surface with edible oil,no odor,moderate taste,ready-to-eat or pure water brewing,without cooking. |
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