An-Ran Zheng

Microbial community succession in raw milk determines its quality and storage period. In this study, carbon dioxide (CO₂) at 2000 ppm was used to treat raw milk to investigate the mechanism of extending the shelf life of raw milk by CO₂ treatment from the viewpoint of microbial colonies and metabolites. The results showed that the shelf life of CO₂-treated raw milk was extended to 16 days at 4 °C, while that of the control raw milk was only 6 days. Microbiomics analysis identified 221 amplicon sequence variants (ASVs) in raw milk, and the alpha diversity of microbial communities increased (p < 0.05) with the extension of storage time. Among them, Pseudomonas, Actinobacteria and Serratia were the major microbial genera responsible for the deterioration of raw milk, with a percentage of 85.7%. A combined metagenomics and metabolomics analysis revealed that microorganisms altered the levels of metabolites, such as pyruvic acid, glutamic acid, 5′-cmp, arginine, 2-propenoic acid and phenylalanine, in the raw milk through metabolic activities, such as ABC transporters, pyrimidine metabolism, arginine and proline metabolism and phenylalanine metabolism, and reduced the shelf life of raw milk. CO₂ treatment prolonged the shelf life of raw milk by inhibiting the growth of Gram-negative aerobic bacteria, such as Acinetobacter guillouiae, Pseudomonas fluorescens, Serratia liquefaciens and Pseudomonas simiae.

Microbial community succession in raw milk determines its quality and storage period. In this study, carbon dioxide (CO2) at 2000 ppm was used to treat raw milk to investigate the mechanism of extending the shelf life of raw milk by CO2 treatment from the viewpoint of microbial colonies and metabolites. The results showed that the shelf life of CO2-treated raw milk was extended to 16 days at 4 ℃, while that of the control raw milk was only 6 days. Microbiomics analysis identified 221 Amplicon Sequence Variants (ASVs) in raw milk, and the alpha diversity of microbial communities increased (P < 0.05) with the extension of storage time. Among them, Pseudomonas, Actinobacteria and Serratia were the major microbial genus responsible for the deterioration of raw milk, with a percentage of 85.7%. A combined metagenomics and metabolomics analysis revealed that microorganisms altered the levels of metabolites, such as pyruvic acid, glutamic acid, 5'- cmp, arginine, 2-propenoic acid, and phenylalanine in the raw milk through metabolic activities, such as ABC transporters, pyrimidine metabolism, arginine and proline metabolism and phenylalanine metabolism, and reduced the shelf life of the raw milk. CO2 treatment prolonged the shelf life of the raw milk by inhibiting the abundance of Gram-negative aerobic bacteria, such as Acinetobacter guillouiae, Pseudomonas fluorescens, Serratia liquefaciens and Pseudomonas simiae.

Goji berry (Lycium barbarum L., LBL) is a good source of carotenoids, while the bioaccessibility of various types of LBL carotenoids has not been explored. In the study, eight carotenoids, three carotenoid esters and two carotenoid glycosylated derivatives were identified by a non−targeted metabolomics approach. The dried LBL (DRI), LBL in water (WAT), and LBL in “Baijiu” (WIN) were used to recreate the three regularly chosen types of utilization, and the in vitro digestion model showed that the bioaccessibility of the carotenoids increased significantly from the oral to the gastric and intestinal phase (p < 0.05). The bioaccessibility of LBL carotenoids was the most elevated for DRI (at 28.2%), followed by WIN and WAT (at 24.9% and 20.3%, respectively). Among the three carotenoids, zeaxanthin dipalmitate showed the highest bioaccessibility (51.8–57.1%), followed by β−carotene (51.1–55.6%) and zeaxanthin (45.2–56.3%). However, the zeaxanthin from DRI exhibited significantly higher bioaccessibility (up to 58.3%) than WAT and WIN in both the gastric and intestinal phases (p < 0.05). Results of antioxidant activity tests based on DPPH, FRAP, and ABTS showed that the addition of lipids improved the bioaccessibility of the carotenoids. (p < 0.05).