Study On Growth Kinetics Model And Shelf Life Prediction Model Of Specific Spoilage Bacteria In Pixian Bean Paste

Pixian bean paste is a specialty of Pidu district(formerly known as Pixian County)of Chengdu City.It is a good seasoning in Sichuan cuisine and is known as"the soul of Sichuan cuisine".However,in the process of production,processing,transportation and storage of Pixian bean paste,due to the pollution of specific spoilage bacteria and the re fermentation of beneficial microorganisms,the flavor of Bean paste became worse and sour,which seriously affected the product quality and shelf life.In this paper,the specific spoilage bacteria of Pixian bean paste were screened and identified,the microbial growth kinetics model of Pixian bean paste was constructed,and the shelf life of products was predicted,which provided a theoretical basis for the quality and safety of Pixian bean paste.The main research contents are as follows(1)Isolation and identification of spoilage bacteria from Pixian bean paste.Three strains were isolated from a brand of Pixian Bean paste,which were labeled as S4,S6 and S13 respectively.Based on the morphological characteristics,physiological and biochemical characteristics and 16S rDNA sequence analysis,S4 was identified as Pichia mbranae faciens,S6 as Bacillus subtilis,and S13 as Enterococcus faecalis The phylogenetic tree of faecalis was constructed.(2)Microbial effect of quality change of Pixian bean paste and identification of specific spoilage bacteria.The three strains S4,S6 and S13 were inoculated into Pixian bean paste respectively.After aseptic sealing,they were placed at room temperature(about 25?)and sampled every 24 hours.The specific spoilage bacteria were determined by analyzing the physical and chemical indexes of the products and sensory evaluation.The results showed that the three strains S4,S6 and S13 had different effects on the degree of product spoilage.The three strains S4,S6 and S13 were identified as the specific spoilage bacteria of Pixian bean paste.The minimum amount of spoilage of strains S4,S6 and S13 were 12.0×10~4cfu/g,13.4×10~4cfu/g and17.8×10~4cfu/g,respectively.It was concluded that Enterococcus faecalis S13 was the main spoilage bacteria causing deterioration of Pixian Bean paste.(3)Establishment of growth kinetics model and shelf life prediction of Enterococcus faecalis S13 in Pixian bean paste.A certain amount of S13 was inoculated into four samples of Pixian bean paste,which were cultured at 4?,12?,20?and 30?respectively.The samples were taken every 24 hours to detect the number of S13.The Gompertz function mathematical model was used to build the growth kinetics model of S13 Enterococcus faecalis,and the shelf life prediction model of Pixian bean paste was initially established,and the model was verified.The results show that Gompertz function can well describe the growth dynamics of S13 in Pixian bean paste;according to the influence of temperature on the maximum specific growth rate and delay time,the beleharadek model has a good linear relationship;in the verification experiment,the deviation and accuracy of the model are 1.011 and 1.015 at 9?.Under the condition of 26?,the deviation is 1.012 and the accuracy is 1.021.