Analysis Of Dominant Spoilage Bacteria At Different Temperatures And Construction Of Shelf Life Prediction Model Of Flammulina Velutipes

The Flammulina velutipes is crispy and tender with high water content and rich nutrition.Strong respiratory metabolism,rapid senescence and microbial infection lead to a short shelf life and low nutritional value for postharvest F.velutipes.Therefore,it is of great practical significance for the quality control of F.velutipes to determine the species of dominant spoilage bacteria in the storage process and to quickly predict the shelf life of F.velutipes fruiting bodies.In this study,through separation and purification and return verification,the species of dominant spoilage bacteria of F.velutipes at different storage temperatures were identified;we analyzed the effect of temperature on the shelf quality of F.velutipes by regularly measuring the sensory quality and physical and chemical quality at different temperatures;The kinetics models combined with the Arrhenius equation were used to establish shelf life prediction models based on quality indexes;whereas,the Gompertz model combined with the Belehradek equation were used to establish a growth trend and shelf life prediction model for F.velutipes based on the presence of the total baterial account.We have done these works in order to provide theoretical basis and reference for microbial control and shelf life prediction during storage and circulation of F.velutipes.The main results obtained in this study were as follows:1.The quantity change of bacteria and the species of dominant spoilage bacteria of F.velutipes under different storage temperatures were determined.According to the results of the return test and 16S rDNA analysis of spoilage bacteria,the identification results and the spoilage ability were as follows:The dominant spoilage bacteria and corruptive ability at 4?were Ewingella Americana>Serratia quinivorans;the dominant spoilage bacteria and corruptive ability at 15?were Ewingella Americana>Bacillus safensis>Serratia quinivorans.The dominant spoilage bacteria and corruptive ability at 25?were Ewingella Americana>Bacillus safensis>Enterobacter ludwigii.2.The changes of sensory quality and physicochemical quality of F.velutipes under different shelf storage temperature were obtained.The results showed that low temperature could inhibit the sensory quality deterioration and delay the loss of soluble protein,soluble solids and other nutrients of F.velutipes.It could reduce the weight loss,prevent the microbial infection,and delay the rise of disease index and decay index of F.velutipes.It also inhibited the activities of PPO and POD,delayed the browning and increased the content of malondialdehyde and prevented the peroxidation of membrane lipid.3.The quality deterioration kinetic models and shelf life prediction models based on quality index were established.The results showed that the weight loss rate,decay index,whiteness value,browning degree,soluble protein content and soluble solid content could be the key quality factors of the model.The fitting coefficient R~2of kinetic models and the Arrhenius equation were all above 0.90 and the error of shelf life prediction models were within±10%,which could well predict the quality deterioration and the remaining shelf life at different storage temperatures of postharvest F.velutipes in the range of 4-25?.The prediction accuracy of these models based on soluble solid content was the highest.4.The growth trend and shelf life prediction model based on the total bacterial counts were established.The fitting coefficient of the first-order model of microbial growth at different shelf storage temperature are more than 0.90,the B_f and A_f were close to 1,which could well predict the trend of bacterial growth at different temperatures;the fitting coefficient of the second-order model of microbial growth were more than 0.90 and the residual value of the predicted value and the measured value were less than 0.1,which could accurately reflect the influence of ambient temperature on the parameters of the first-order model of bacterial growth.The shelf life prediction errors were within 10%.The model can accurately predict the shelf life of postharvest F.velutipes in the range of 4-25?.All in all,F.velutipes was susceptible to enterobacteria infection such as Ewingella Americana during postharvest storage.Low temperature can obviously inhibit the growth and reproduction of microorganisms and maintain certain sensory quality and physicochemical quality.These models could well predict the quality deterioration and shelf life of F.velutipes after harvest within the range of 4-25?.