Effect of Packaging Method and Storage Temperature on Bacterial Load, Diversity and Metabolic Pathways in Mutton

To investigate the effects of packaging method and storage temperature on the bacterial load, diversity and metabolic pathways in mutton, postportem mutton was stored in air packaging (AP), vacuum packaging (VP) or skin packaging (SP) for 30 days at chilled ((4 ± 1) ℃) or superchilled temperature ((−1.7 ± 0.2) ℃). The bacterial community composition during the storage period was analyzed by a combination of plate counting and high-throughput sequencing. The results showed that total viable count (TVC), Lactobacillus count, Pseudomonas count, Staphylococcus/Micrococcus count, mold and yeast count, and psychrophilic bacterial count were all lower in the SP group than in the AP and VP groups, and all the bacterial counts were significantly lower in the superchilled storage group than in the chilled storage group. The bacterial diversity showed a decreasing trend with storage time, and it was more complex in the chilled storage group than in the superchilled storage group. A total of 30 bacterial genera belonging to 10 bacterial phyla were obtained by high-throughput sequencing of the V3–V4 region of the 16S rDNA gene. For all samples, the most abundant phyla were Proteobacteria and Firmicutes. Pseudomonas was the dominant genus in the AP group but less abundant in the SP and VP groups. Carnobacterium, Brochothrix and Lactobacillus were the dominant genera at the end of storage for all three groups. The Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis revealed that carbohydrate, amino acid and nucleotide metabolism were the major metabolic pathways during the storage of mutton. Amino acid metabolism was dominant during the early storage period, while carbohydrate and nucleotide metabolism were dominant during the late storage period. The difference in metabolic abundance was mainly attributed to the difference in microflora structure caused by packaging methods and storage temperatures. In conclusion, SP combined with superchilled temperature can reduce the microbial load and community diversity in mutton during storage, helping to maintain the quality of mutton.