Investigation on the Microbial Diversity of Fresh-Cut Lettuce during Processing and Storage Using High Throughput Sequencing and Their Relationship with Quality

Microbial community distribution in vegetables can affect their quality. This study analyzed the distribution of the microbial community at various stages during processing and storage with the microbial diversity analysis, and evaluated the correlation between the dominant bacteria and sensory quality of lettuce using correspondence analysis with multiple regression analysis. Results showed that the process of washing, cutting, then disinfection and dewatering could change the community distribution and dominant bacteria in lettuce, and maintain better texture, morphology, aroma, color qualities of lettuce. The total number of colonies and relative abundance of Xanthomonas in fresh-cut lettuce decreased, while Afipia and Ralstonia increased during processing and pre-storage (storage for 6 h, 12 h and 1 d). After storage for 3 d, the total number of colonies in lettuce increased (more than 5 log CFU/g), especially the relative abundance of Pseudomonas, which led to the obvious deterioration of the sensory quality of lettuce. Throughout the process, the number of Bacillus cereus, Staphylococcus aureus, and E. coli was less than 100 CFU/g and 3 MPN/g. The number of typical pathogenic bacteria, Salmonella, Listeria monocytogenes and E. coli O157:H7, was below the detection limit. Overall, the prevention and control of psychrotrophic Pseudomonas in lettuce was still necessary. These results will provide useful information for the fresh-cut lettuce industry.