The effect of storage at 25 °C on proteins in human milk

The effect of storage of milk at 25 °C upon the major human milk proteins was investigated. Milk samples (n = 8) were collected and stored at 25 °C for 72 h. The degree of proteolysis in the skim milk and fat globule protein fractions, protein oxidation and milk lipase activity were measured at regular time intervals. β-casein was rapidly hydrolyzed, with 38 ± 5% (mean ± SEM) remaining after 72 h. The immunological proteins, secretory IgA and lactoferrin, appeared to be resistant to proteolysis. The lipase activity was reduced after 2 h of storage (p < 0.001). Protein oxidation was not observed. These results highlight the importance of appropriate milk handling when analyzing the protein composition of milk in a laboratory. Further investigation is required to determine whether the observed effects of storage upon milk proteins are of clinical importance.