Breastfeeding and the working mother: effect of time and temperature of short-term storage on proteolysis, lipolysis, and bacterial growth in milk

• Published in: Pediatrics (Evanston) Vol. 97; no. 4; p. 492
• Main Authors: Hamosh, M. (Georgetown University Medical Center, Washington, DC.), Ellis, L.A, Pollock, D.R, Henderson, T.R, Hamosh, P
• Format: Journal Article
• Language: English
• Published: United States 01.04.1996
• Subjects: ACIDE GRAS; ACIDOS GRASOS; Adult; ALIMENTOS; ALMACENAMIENTO; Amino Acids - analysis; Analysis of Variance; BACTERIA; Bacteria - growth & development; Breast Feeding; Colony Count, Microbial; CONTEO DE CELULAS; DISTRICT DE COLUMBIA; DISTRITO DE COLUMBIA; DURACION; DUREE; Fatty Acids, Nonesterified - analysis; Female; FEMME; GRASA DE LA LECHE; Humans; Hydrogen-Ion Concentration; Infant; Infant, Newborn; LACTACION; LACTATION; LAIT; LAIT HUMAIN; LECHE; LECHE HUMANA; Lipids - analysis; LIPOLISIS; LIPOLYSE; Lipolysis; MAIN D'OEUVRE FEMININE; MANO DE OBRA FEMENINA; MATIERE GRASSE DU LAIT; MICROORGANISME; MICROORGANISMOS; Milk Proteins - analysis; Milk Proteins - chemistry; Milk, Human - chemistry; Milk, Human - microbiology; Milk, Human - physiology; Mothers; MUJERES; NUMERATION CELLULAIRE; PRODUIT ALIMENTAIRE; PROTEINAS; PROTEINE; PROTEOLISIS; PROTEOLYSE; STOCKAGE; TEMPERATURA; TEMPERATURE; Time Factors; Women, Working
• ISSN: 0031-4005; 1098-4275
• DOI: 10.1542/peds.97.4.492

Background. Women who breastfeed have to store expressed milk while at work for later feeding to their infants; however, storage conditions are often not optimal. Objective. To assess microbial growth and stability of milk protein and lipid at 15 degrees C to 38 degrees C for up to 24 hours. Methods. Sixteen healthy women who breastfed exclusively, either at home (n = 11) or who expressed milk for their infants (n = 5), were studied during early (1 month) or late (5 to 6 months) lactation. Expressed milk was stored at 15 degrees C, 25 degrees C, and 38 degrees C for 1 to 24 hours for quantitation of pH, proteolysis, and lipolysis; bacterial growth was quantified at 0, 4, 8, and 24 hours of storage. Results. Milk pH decreased 2 units by 24 hours of storage at all temperatures tested. Proteolysis was minimal during milk storage at 15 degrees C or 25 degrees C for 24 hours and was apparent only after 24 hours of storage at 38 degrees C. Lipolysis was rapid, starting in the first hours of storage and progressing to 8% at 24 hours. Thus, while the greatest increment in proteolysis products was a 40% increase above baseline after 24 hours of storage at 38 degrees C, free fatty acid concentration at this storage time was 440% to 710% higher than in freshly expressed milk. Bacterial growth was restricted mainly to nonpathogens, was minimal at 15 degrees C throughout the 24 hours of storage, was low at 25 degrees C for the first 4 to 8 hours, and was considerably higher at 38 degrees C even during the relatively short period of 4 hours. Conclusions. Storage of human milk is safe at 15 degrees C for 24 hours, whereas at 25 degrees C it is safe for 4 hours. Milk should not be stored at 38 degrees C. Minimal proteolysis during storage suggests that milk proteins probably maintain their structure and function during short-term storage, while the marked lipolysis might slow bacterial growth during this time