Microbial Properties of Raw Milk throughout the Year and Their Relationships to Quality Parameters

Abstract

Raw milk microbiota is complex and influenced by many factors that facilitate the introduction of undesirable microorganisms. Milk microbiota is closely related to the safety and quality of dairy products, and it is therefore critical to characterize the variation in the microbial composition of raw milk. In this cross-sectional study, the variation in raw milk microbiota throughout the year (n = 142) from three farms in China was analyzed using 16S rRNA amplicon sequencing, including α and β diversity, microbial composition, and the relationship between microbiota and milk quality parameters. This aimed to characterize the contamination risk of raw milk throughout the year and the changes in quality parameters caused by contamination. Collection month had a significant effect on microbial composition; microbial diversity was higher in raw milk collected in May and June, while milk collected in October and December had the lowest microbial diversity. Microbiota composition differed significantly between milk collected in January–June, July–August, and September–December (p < 0.05). Bacterial communities represented in raw milk at the phylum level mainly included Proteobacteria, Firmicutes and Bacteroidota; Pseudomonas, Acinetobacter, Streptococcus and Lactobacillus were the most common genera. Redundancy analysis (RDA) found strong correlations between microbial distribution and titratable acidity (TA), fat, and protein. Many genera were significantly correlated with TA, for example Acinetobacter (R = 0.426), Enhydrobacter (R = 0.309), Chryseobacterium (R = 0.352), Lactobacillus (R = −0.326), norank_o__DTU014 (R = −0.697), norank_f__SC-I-84 (R = −0.678), and Subgroup_10 (R = −0.721). Additionally, norank_f__ Muribaculaceae was moderately negatively correlated with fat (R = −0.476) and protein (R = −0.513). These findings provide new information on the ecology of raw milk microbiota at the farm level and contribute to the understanding of the variation in raw milk microbiota in China.

Development of a real-time loop-mediated isothermal amplification method for monitoring Pseudomonas lurida in raw milk throughout the year of pasture

“…appears in raw milk every season, which indicates that it is a bacterium, and that its thermostable alkaline proteases may play an important role in raw milk spoilage ( Jonghe et al, 2011 ; Li et al, 2019 ). A previous study analyzed the microbial diversity of year-round raw milk from three pastures in the Hebei province by using high-throughput sequencing, detected the bacteria responsible for contaminating raw milk at different times, and investigated the correlation between these bacteria and raw milk quality parameters ( Yuan et al, 2022 ). The results showed that psychrophilic bacteria in all three pastures were a serious threat to the quality of raw milk.…”

Grape Pomace in Ewes Diet Affects Metagenomic Profile, Volatile Compounds and Biogenic Amines Contents of Ripened Cheese

“…Microorganisms belonging to the phylum of Proteobacteria such as Acinetobacter (family Moraxellaceae) and Pseudomonas (family Pseudomonaceae) characterize Ctrl and GP+ cheeses after 2 days of ripening. Acinetobacter is a Gram-negative, psychrotrophic bacteria, that colonize teat canal and has been found in feces samples and as contaminant of raw milk [35]. Pseudomonas is the most important psychrotrophic bacteria in raw milk, coming from natural environment [36] and has been related to hygiene conditions [37,38].…”

Prevalence and Antibiotic Resistance of Bacillus sp. Isolated from Raw Milk

“…Non-compliance with the hygiene standards of its acquisition makes it difficult to avoid the contamination of milk with microorganisms [2]. The level of microbiological contamination of milk depends on several factors such as animal health, farm sanitary conditions, milking hygiene, and milk storage temperature [3,4]. In most cases, unless the animal is suffering from a mammary gland infection or systemic disease, the milk produced by a mammary gland should not contain bacteria, although it is easily contaminated with microbes living on the animal's skin during milking.…”

“…The dominant microbiota of chilled raw milk is psychrotrophic bacteria, capable of producing undesirable proteolytic and lipolytic enzymes, causing adverse changes in dairy products [3,4,8]. Among the most significant bacteria causing spoilage of dairy products are bacteria belonging to the genus of psychrotrophic Bacillus.…”