Microbiological Examination of Pasteurized, Deaerated Human Milk

Three composites of human milk samples were subjected to different processing conditions: (1) deaerated, vacuum packaged in metalized polyester bags and pasteurized at 56°C for 8 min; (2) vacuum packaged and pasteurized; (3) vacuum packaged. On days 0, 4, 7, 14, 28, 64, and 96 of storage, each treatment was analyzed for dissolved oxygen content and viable microflora. On days 0, 4, and 14, randomly selected isolates from each treatment were identified to the species level. Heat treatment of the milk samples reduced the number of viable microorganisms and resulted in a shift in the type of bacteria in the milk. Pasteurized samples contained primarily non-pathogenic skin commensals, while non-pasteurized samples were populated by species of Pseudomonas and other Gram negative microorganisms, including potential pathogens. Deaeration did not affect either the number or types of microorganisms surviving the heat treatment.