Study On Quality Changes And Microwave Preservation Technology Of Fresh Wet Rice Noodles During Storage

Fresh wet rice noodles,as a traditional food in China,were very popular because of their convenience,smooth taste,good chewiness and the fragrance of rice itself.They have a wide consumption market in Jiangxi,Guangdong,Fujian and other regions of China.However,due to the high moisture and starch content of fresh wet rice noodles and the current production pattern of small workshops,a series of quality deterioration reactions are easily occurred in the process of production,circulation and storage,resulting in reduced food quality and shortening shelf life,easily causing public food safety problems,and further hindering the development of the industrialization of fresh wet rice noodles.Therefore,it is the key scientific problem to determine the key factors of quality deterioration during the storage of fresh wet rice noodles and to take effective control measures to prolong their shelf life.According to this,this paper takes the representative fresh wet rice noodles in Nanchang,Jiangxi province as the research object.The quality changes of fresh wet rice noodles during storage were studied and the correlation analysis between quality indexes was carried out to determine the key index of quality deterioration.At the same time,the microwave sterilization technology of the main dominant bacteria in fresh wet rice noodles was studied by means of physical measures,and the application effect of the process on the storage quality of fresh wet rice noodles was investigated.This is of great significance for fresh wet rice noodles in storage and preservation,shelf life and industrial development.The main contents and results were shown as follows:1.The purpose of this work was to study the quality change rule of fresh wet rice noodles during storage at 28?and 4?.Besides,the correlation among these quality characteristics was analyzed.The results indicated that the sensory score of fresh wet rice noodles decreased obviously during storage at 28?.The moisture content decreased gradually,and the acidity increased significantly after 1 day.In addition,the brightness?L^*?dimmed,cooking quality decreased obviously,and the hardness,elasticity,cohesiveness and chewiness increased first and then decreased.The microbial indexes were all in logarithmic growth,and the total number of APC accounted for the largest among them,reaching 5.6×10⁶ CFU/g after 0.5 day,exceeding the standard limit.The results of fresh wet rice noodles during storage at 4?showed the sensory score significantly decreased,and the moisture content decreased first and then increased and then decreased.The acidity value maintained 0.1014°T all the time,and the cooking quality generally decreased.The hardness,the adhesiveness,and the chewiness were increased first and then decreased,but the overall elasticity decreased.Besides,the total number of molds and yeasts was in logarithmic growth,and the total number of APC decreased first and then increased,up to 5×10⁶ CFU/g until 7 days,more than the standard limit.The results of correlation analysis showed that microbial indexes were significantly correlated with sensory organs,color difference,moisture content and cooking water absorption for fresh wet rice noodles stored at 28?,while microbial indexes were significantly correlated with sensory organs,color difference,cooking loss rate and texture at 4?,which indicated that the microbial index could be used as a key factor for evaluating the quality deterioration of fresh wet rice noodles.2.The dominant bacteria in fresh wet rice noodles during storage were isolated and identified by selective culture of traditional microorganism and 16S rDNA,and the dominant bacteria composition in fresh wet rice noodles during storage and the main dominant bacteria to determine the quality deterioration of fresh wet rice noodles were also investigated.The results showed that the number of dominant bacteria in fresh wet rice noodles increased logarithmically during storage at 28?,and the total number of APC reached 7.2×10⁶ CFU/g after 1 day,which exceeded the standard limit.Sensory score decreased to 21.1 points,indicating obvious signs of deterioration after 2 days.The flat bacterial colonies with fresh wet rice noodles stored to 2 days were used to isolate and identify dominant bacteria,and the results showed the dominant bacteria were Enterobacteriaceae,Lactobacillus,and Bacillus sp.by phenotypic characterization,and Enterobacter sp.were the main dominant spoilage bacteria by genotype identification.With the extension of storage time,dominant bacteria were gradually single,and Enterobacteriaceae accounted for 51.3%of all the bacteria,which was primarily responsible for the spoilage of fresh wet rice noodles.3.The optimal microwave sterilization condition of the dominant bacteria isolated from the fresh wet rice noodles was optimized by using the response surface method on the basis of single factor experiment.The results showed that the sterilization rate of the dominant bacteria increased with the increase of microwave power and treatment time and the decrease of the mass of the bacterial fluid.According to the response surface optimization and analysis of variance,the optimum technology of microwave sterilization was microwave power of 600 W,liquid weight of 100 g,microwave time of 70.61 s,R²_adj=0.8085,R²=0.8324,indicating that the model fitting proposed by this study are acceptable.The process parameters adjusted after verification showed that the microwave sterilization technology was determined to be:microwave power of 600 W,liquid weight of 100 g,and microwave time of 71 s.Under these conditions,the maximum sterilization rate was up to 92.44%,and the relative error was 1.99%,compared to the theoretical value of 94.32%.The results showed the surface optimization method of microwave sterilization technology was feasible in response,which had certain guiding significance in practice.4.The effect of microwave treatment on the storage quality of fresh wet rice noodles was researched.Fresh wet rice noodles were treated with 600 W microwave power for 71 s and were stored at 28?with the control group without microwave treatment.The results showed that the sensory score,L^*value,a^*value,moisture content and cooking water absorption rate of two experimental groups gradually decreased during storage,and the b^*value,cooking loss rate,the total number of APC gradually increased,and the hardness,elasticity,cohesiveness and chewiness increased firstly and then decreased with time.The control group stored at 36 hours had poor sensory score of only 42.28 points,and the treatment group stored at 60 hours still maintained good sensory score of 63.57 points.In addition,the control group stored at 24 hours had poor cooking absorption rates of 47.98%and cooking loss rates of 2.43%,and the treatment group stored at 60 hours had cooking quality?43.88%,2.76%,respectively?similar to the control group stored at 24 hours.Meanwhile,the total number of APC of the control group stored at 12 hours reached5.9×10⁶ CFU/g,more than the standard limit?8×10⁴ CFU/g?,and the treatment group stored at 36 hours reached 7.5×10⁵ CFU/g,exceeding the standard limit.In conclusion,to a certain extent,microwave treatment could effectively delay quality deterioration of fresh wet rice noodles.