Study On The Changes Of Bacterial Microflora Structure And Microbial Predictive Model In Fresh Duck Meat

In recent years,fresh duck meat has been paid more and more attention in the market.But due to the contamination of microorganisms in the process of slaughter,processing and transportation,as well as the imperfect construction of cold chain in the actual production,and the rich nutrients in the duck meat provide a good material basis for the growth of microorganisms,the quality of fresh duck meat is prone to spoilage,and even resulting in food safety problems.Based on the actual processing,storage and transportation environment,the thesis studied the changes in the quality of fresh duck meat and the microbial flora structure to clarify the more effective evaluation indicators and the dominant spoilage bacteria of fresh duck meat.Based on fluorescent quantitative PCR to construct a rapid detection method for Pseudomonas fluorescens in duck meat,and then build a microbial growth prediction model during cold storage,and with a view to providing theoretical support for the development of fresh duck meat quality control technology development,rapid microorganism detection and monitoring.The main findings are as follows:(1)Research on the quality changes of fresh duck meat during cold storage.Based on the actual production,processing and logistics conditions of the enterprise,studied the quality change rules of the two groups of fresh duck meat products with bacteriostatic treatment and non-bacteriostatic treatment during cold storage.The results showed,during the storage,the sensory score decreased significantly with the extension of storage time,the total number of colonies and TVB-N increased significantly,the overall color of duck meat did not change significantly,and the p H value fluctuated less.Based on the evaluation criteria of microbes,the products with the non-bacteriostatic treatment and bacteriostatic treatment reached the limit standards on the 9th and 15th days,respectively.Antibacterial treatment could suppress the deterioration of fresh products’quality during storage effectively.Comprehensive analysis of various quality indicators and their correlations,Pseudomonas sp.and lactic acid bacteria could be used as more effective indicators for evaluating the quality of fresh duck meat.(2)Based on high-throughput sequencing technology to research the changes of bacterial structure in the processing stage and storage period of fresh duck meat.The results showed,the segmentation operation increased the contamination of microorganisms in duck meat,resulted in a significant increase in the richness and diversity of the microbial community.The combined sterilization treatment of chlorine dioxide and kojic acid reduced the species richness and diversity of the sample,changed the structure of the flora in duck meat,and showed satisfactory sterilization effect.The species richness of products in cold chain transportation increased significantly,indicating that psychrotrophic bacteria keep growth during the short transportation process.Acinetobacter,Enhydrobacter and Chryseobacterium were the predominant bacteria in duck carcass,Acinetobacter,Pseudomonas and Brochothrix were the predominant bacteria in the duck meat after packaging.Differences in processing methods also had a greater impact on the microbial structure of products during refrigeration,at the early cold storage,the main bacterial groups in the products that without sterilization belong to Firmicutes and Proteobacteria,Acinetobacter and Lactococcus mainly,in the products with sterilization,Firmicutes was the dominant phylum,Weissella mainly.Differences in processing methods had little effect on the bacterial structure of duck meat products in the later period of cold storage,the predominant bacterial in two groups of duck meat are both Carnobacterium and Lactococcus.Through predictive analysis of gene function,it was found that carbohydrate metabolism and amino acid metabolism are the main metabolic pathways in products.(3)Construction of rapid detection method for Pseudomonas fluorescens in duck meat based on fluorescence quantitative PCR.Through the optimization of PCR technology system,specific verification,standard curve construction,calculation of amplification efficiency and determination of minimum detection limit,the PCR system was verified and evaluated.The results showed,the constructed system had good amplification efficiency and specificity,and within a certain error range,the established rapid detection method of Pseudomonas fluorescens could be applied to fresh duck meat.The R~2 of the standard curve constructed by pure culture and artificial inoculation were 0.994 and 0.992,the amplification efficiency were 108%and 105%,it showed a good linear relationship and amplification efficiency.The minimum detection limit of the system was 10~2 CFU/g.In the two groups of products,Pseudomonas fluorescens was detected in the duck meat without sterilization,and the number gradually increased with the storage time,Pseudomonas fluorescens was not detected in the products that with sterilization.(4)Construction of prediction model of microbial growth of fresh duck meat during storage.The modified Gompertz model was used to construct a primary growth model of Pseudomonas,LAB and Pseudomonas fluorescens in fresh duck meat at 4℃、10℃、15℃、20℃and 25℃.The Square root model and the Non-linear Arrhenius model was used to describe the effect of temperature on maximum specific growth rate and the lag period.The results showed,the constructed primary growth model could better reflect the growth of Pseudomonas,LAB and Pseudomonas fluorescens at a temperature of 4-25℃,and the secondary growth model could better describe the effect of temperature on maximum specific growth rate and the lag period.The analysis of model parameter showed that the growth of Pseudomonas,LAB and Pseudomonas fluorescens in fresh duck meat was significantly inhibited under low temperature environment.As the storage temperature increases,the maximum specific growth rate gradually increased and the lag period gradually decreased.The antibacterial treatment prolonged the lag period of Pseudomonas in duck meat,while the lag period of LAB in duck meat was significantly lower.Based on the growth models of Pseudomonas,LAB and Pseudomonas fluorescens,a shelf life prediction model of fresh duck meat was constructed.