Microbial Diversity and Non-volatile Metabolites Profile of Low-Temperature Sausage Stored at Room Temperature.

Sausage is a highly perishable food with unique spoilage characteristics primarily because of its specific means of production. The quality of sausage during storage is determined by its microbial and metabolite changes. This study developed a preservative-free low-temperature sausage model and coated it with natural casing. We characterized the microbiota and non-volatile metabolites in the sausage after storage at 20°C for up to 12 days. Bacillus velezensis was the most prevalent species observed after 4 days. Lipids and lipid-like molecules, organoheterocyclic compounds, and organic acids and their derivatives were the primary non-volatile metabolites. The key non-volatile compounds were mainly involved in protein catabolism and ß-lipid oxidation. These findings provide useful information for the optimization of sausage storage conditions.

Comparative analysis of whey proteins in donkey colostrum and mature milk using quantitative proteomics.

Donkey milk is attracting increasing attention as a nutritional milk source similar to human milk. In this study, we carried out qualitative and quantitative analysis of the donkey whey proteome using a label-free proteomic approach, combined with parallel reaction monitoring (PRM) as a validation method. A total of 300 whey proteins were identified in donkey colostrum (DC) and donkey mature (DM) milk, of which 18 were differentially expressed (P < 0.05) between the two types of milk. Gene ontology (GO) analysis showed that differentially and uniquely expressed proteins were mainly involved in cellular processes, response to stimulus, metabolic processes, and biological regulation. Their molecular functions included binding, catalytic activity, and molecular functional regulation, and their main annotated areas of origin were the cell, cell-part, and the extracellular region. Most differentially and uniquely expressed proteins were linked with malaria, systemic lupus erythematosus, or antigen processing and presentation. Our results provide insight into the complexity of the donkey whey proteome and molecular evidence for nutritional differences between different lactation stages.

Quantitative proteomic analysis of milk fat globule membrane (MFGM) proteins from donkey colostrum and mature milk.

The composition and functions of milk fat globule membrane (MFGM) proteins are important indicators of the nutritional quality of milk. However, these characteristics of MFGM proteins in donkey milk are unknown at different lactation periods. We characterized and identified MFGM proteins in donkey milk at two lactation periods using label-free proteomics. A total of 947 MFGM proteins were found. There were 902 and 913 MFGM proteins in donkey colostrum and mature milk, respectively. The differentially expressed MFGM proteins were classified into different Gene Ontology annotations. The biological process subgroups containing the most MFGM proteins mainly included cellular process, metabolic process, biological regulation, and regulation of biological processes. Donkey MFGM proteins participated in several Kyoto Encyclopedia of Gene and Genomes (KEGG) pathways at different lactation stages, such as endocytosis, thermogenesis, Alzheimer's disease, cancer, and human papillomavirus infection. The knowledge gained in this study may provide theoretical insights and guidance for the future development of novel infant formulae.

Quantitative analysis of amino acids in human and bovine colostrum milk samples through iTRAQ labeling.

BACKGROUND: The types and quantity of proteins vary widely between bovine and human milk, with corresponding differences in free and hydrolytic amino acids. In this study, the free and hydrolytic amino acids of bovine and human colostrum were for the first time qualitatively and quantitatively determined using isobaric tags for relative and absolute quantification technology combined with liquid chromatography tandem mass spectrometry detection. RESULTS: Total free amino acid content was 0.32 g L-1 and 0.63 g L-1 in bovine and human colostrum respectively, with free amino acid content in human colostrum twice that of bovine colostrum. However, total hydrolytic amino acid content was 4.2 g L-1 and 2.2 g L-1 in bovine and human colostrum respectively. We found that the hydrolytic amino acid content in bovine colostrum was higher than that in human colostrum; however, the amount of free amino acids and the overall amino acid content in human colostrum were respectively substantially higher and more varied than in bovine colostrum. CONCLUSION: Our findings revealed differences between bovine and human colostrum, with these data providing the basis for further research into amino acid metabolomics and infant formula. © 2018 Society of Chemical Industry.

Quantitative N-glycoproteomics of milk fat globule membrane in human colostrum and mature milk reveals changes in protein glycosylation during lactation.

Milk fat globule membrane (MFGM) proteins have recently gained increasing attention, due to their significant biological function. However, the glycosylation of proteins in human MFGM during lactation has not been studied in detail. In this study, through mass spectroscopy-based N-glycoproteomics, we analyzed protein glycosylation of human MFGM. A total of 912 N-glycosylation sites on 506 N-glycoproteins were identified in human colostrum and mature milk MFGM. Among them, 220 N-glycoproteins with 304 N-glycosylation sites were differentially expressed in colostrum and mature milk MFGM. Gene Ontology (GO) analysis revealed various biological processes, cellular components, and molecular functions of the differentially expressed N-glycoproteins. Specifically, these glycoproteins were involved in biological processes such as single-organism processes, biological regulation, regulation of biological processes, response to stimulus and localization; were cellular components in organelles, membranes, and the extracellular region; and had different molecular functions such as protein binding, receptor activity, and hydrolase activity. KEGG pathway analysis suggested that the majority of the differentially expressed N-glycoproteins were associated with phagosome, cell adhesion molecule and some disease-related pathways. Our results provide an in-depth understanding of the quantitative changes in N-glycosylation of proteins in human colostrum and mature MFGM, and extend our knowledge of the N-glycoproteome and of the distribution of N-glycosylation sites in human MFGM during lactation, providing insight into the biological functions of the highlighted glycoproteins.