Effect of Frozen Storage on Lipids and Volatile Compounds of Human Milk

The objective of this study was to investigate the effects of different frozen storage conditions (freezing at −18 and −60 ℃, and quick freezing at -60 ℃; 60 and 180 days) through measuring the contents of fat, non-esterified fatty acids (NEFA), and lipid peroxide (LPO), fatty acid composition, the microstructure of milk fat globules and volatile compounds in human milk. The results showed that the fat content decreased significantly, whereas NEFA and LPO contents increased significantly after frozen storage at −18 ℃ for 60 and 180 days; the content of unsaturated fatty acid (UFA) decreased after 180 days; the milk fat globule membrane was destroyed and lipid accumulation was observed; the contents of off-odor compounds such as aldehydes and acids increased significantly during frozen storage. Storage at −60 ℃ and at −60 ℃ with quick freezing had less impact on fat composition compared to −18 ℃. For instance, no significant difference in fat content was found compared to fresh human milk, despite a slight increase in the contents of NEFA, LPO, and off-odor compounds, and a slight increase in the content of long chain polyunsaturated fatty acids after storage at −60 ℃ for 180 days. Furthermore, the structure of milk fat globules was damaged much less at −60 ℃ than −18 ℃, and the increase in the contents of off-odor compounds was slowed down. Storage at −60 ℃ with quick freezing was more effective in maintaining the original flavor of human milk than −60 ℃. Therefore, we concluded that fast freezing at ultra-low constant temperature has little effect on the fatty acid composition of human milk and protects the physiological properties of lipids, ensuring the quality of human milk feeding, and thus can be considered as the best choice for human milk storage.