Characteristics of sow milks at different lactation stages and their frozen storage stabilities

Evolution of bacterial flora in raw yak milk and its effect on quality characteristics during frozen storage

Due to the scarcity of yak milk in Tibetan areas, local herders primarily use traditional freezing methods for preservation. However, the extent of microbial contamination in raw yak milk during frozen storage and its impact on milk quality remains largely unexplored. This study analyzed the changes in bacterial populations and quality of raw yak milk stored at -18 °C for 6 months. The results indicated that, compared to fresh milk, the freshness of yak milk showed no significant change after 2 months of frozen storage (P > 0.05). After 4 months, the bacterial diversity of flora in yak milk increased significantly, with Pseudomonas and Acinetobacter emerging as the dominant psychrophilic bacteria. Correspondingly, the expression of metabolic pathways related to quality deterioration increased, with a significant increase in physicochemical indicators such as acidity, proteolysis degree, acid value and fat oxidation degree (P < 0.05). Extending the frozen storage to 6 months resulted in a slight but no significant decrease in bacterial diversity, with no significant difference in quality deterioration compared to the 4-month group (P > 0.05). Correlation analysis further revealed that Acinetobacter and Psychrobacter were significantly positively correlated with quality deterioration of frozen milk (P < 0.05). In summary, when frozen for more than 4 months, raw yak milk exhibited the highest bacterial diversity and predicted the most abundant metabolic pathways, with dominant psychrophilic bacteria massive proliferation leading to a decline in quality and safety.

Evaluation of Fatty Acid Distributions and Triacylglycerol Species in Sow Milk and Commercial Piglet Formulas: A Comparative Study Based on Fat Sources and Lactation Stages

Total fatty acid and sn-2 fatty acid compositions, and triacylglycerol (TAG) species in 130 sow colostrum, 100 sow milk, and 22 piglet formula samples were analyzed in the present study. Significant differences were found in concentrations of medium chain-saturated fatty acids (MC-SFAs) and distributions of palmitic acid (P) and oleic (O)/linoleic (L) acid. The levels of MC-SFAs in sow colostrum and sow milk fats (2.4-3.1%) were significantly lower than those in piglet formulas (7.9-27.2%). Approximately 63% of palmitic acid was located at the sn-2 position in both sow colostrum and milk fats, which was significantly higher than in piglet formula fats (21.1-39.1%). Correspondingly, only 17.8-28.3% of oleic and linoleic acids were at the sn-2 position in sow milk fats, contributing to their typical triacylglycerol structure in sow colostrum and milk, whose palmitic acid connected to the sn-2 position and unsaturated fatty acids located at the sn-1,3 positions. Sow colostrum, milk, and piglet formulas were notably distinguished into three groups based on their fatty acids and TAGs, among which triacylglycerols were the most differentiated index. A total of 51 TAG species (including their isomers) differed significantly between sow colostrum and milk and piglet formulas. OPL and OPO were the most important differentiating TAGs. The large amount of sn-2 esterified palmitic acid plays a key role in improving the absorption of fat and calcium. The results provide suggestions for design of sow milk fat equivalents.