The residual core microbiota in pasteurized milk mainly affect the qualities of products through pyruvate metabolism and specific amino acids biosynthesis pathways

Pasteurized milk is highly regarded for its ability to effectively retain nutrients and sensory quality, but its shelf life is limited by the heat-resistant microorganisms and their metabolic products remaining during the mild sterilization process. To solve this problem, the key is to identify the core residual flora and its metabolic network that lead to quality degradation. In this study, pasteurized milk stored at 4 ℃ for 0, 6, 9, and 12 days was examined to explore the changes in physicochemical properties, microbial communities, and functional metabolism during storage. Physicochemical analysis showed a slight decrease in fat, protein, and lactose content and a significant increase in acidity, particle size, and yellowness during storage. Among three pasteurization treatments (65 ℃/30 min, 75 ℃/15 s, and 85 ℃/15 s), the 75 ℃/15 s protocol optimally preserved nutrients and sensory quality, providing critical parameters for process optimization. Metagenomic analysis by Illumina HiSeq sequencing platform showed that Acinetobacter, Pseudomonas and Lactococcus might be the main core microflora leading to the deterioration of pasteurized products during storage. Pasteurized milk processed for 75 ℃/15 s can maintain good quality when stored at 4 ℃ for 0-9 days. Storing at 4℃ for 9 days may be the key storage point for microbial dynamics. Functionally, genes related to carbohydrate metabolism, amino acid metabolism, and energy metabolism increased with storage time. These metabolic pathways are crucial for microbial growth and may affect the nutritional composition and quality of pasteurized milk. Core microbiota primarily impacted milk quality through pyruvate metabolism and valine, leucine, and isoleucine biosynthesis pathways, leading to changes in acidity, bitterness, and texture. This study provides a basis for the monitoring and quality safety management of the main microorganisms and active metabolites during the production, processing and storage of pasteurized milk, and lays a foundation for obtaining high-quality pasteurized milk with long shelf life.