Changes in properties of human milk under different conditions of frozen storage

[Display omitted] •−30 °C is the appropriate temperature for preserving human milk at home.•Freezing at −30 °C and lower can effectively retain microorganisms in human milk.•Freezing at −30 °C and lower reduces the loss of active proteins in human milk.•Freezing at −30 °C and lower reduces lipid hydrolysis degree.•−18 °C quick freezing has no significant advantage in preserving human milk. Human milk is the best source of nutrition for infants. Lower freezing temperatures and faster freezing rates allow for better preservation of human milk. However, research on the freezing conditions of human milk is limited. This study investigated the effectiveness of quick freezing and suitable freezing conditions for home preservation. Human milk was stored under different freezing conditions (−18 °C, −18 °C quick freezing, −30 °C, −40 °C, −60 °C, and − 80 °C) for 30, 60, and 90 days and then evaluated for changes in the microbial counts, bioactive protein, and lipid. The results showed that the total aerobic bacterial and Bifidobacteria counts in human milk after storage at freezing temperatures of − 30 °C and lower were closer to those of fresh human milk compared to − 18 °C. Furthermore, the lysozyme loss, lipid hydrolysis degree, and volatile organic compound production were lower. However, −18 °C quick freezing storage was not markedly different from −18 °C in maintaining human milk quality. Based on the results, for household and environmental reasons, the recommended temperature for storing human milk is suggested as −30 °C.