Breastfeeding and the working mother: effect of time and temperature of short-term storage on proteolysis, lipolysis, and bacterial growth in milk.
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
Top 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 at 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.
Hamosh
M
M
Department of Pediatrics and Physiology and Biophysics, Georgetown University Medical Center, Washington, DC 20007, USA.
Ellis
L A
LA
Pollock
D R
DR
Henderson
T R
TR
Hamosh
P
P
D000328:Adult; D000596:Amino Acids / Q000032:analysis; D000704:Analysis of Variance; D001419:Bacteria / Q000254:growth & development*; D001942:Breast Feeding; D015169:Colony Count, Microbial; D005230:Fatty Acids, Nonesterified / Q000032:analysis; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007223:Infant; D007231:Infant, Newborn; D007774:Lactation; D008055:Lipids / Q000032:analysis; D008066:Lipolysis; D008894:Milk Proteins / Q000032:analysis / Q000737:chemistry*; D008895:Milk, Human / Q000737:chemistry* / Q000382:microbiology* / Q000502:physiology; D009035:Mothers; D013696:Temperature; D013997:Time Factors; D014931:Women, Working
D000596:Amino Acids; D005230:Fatty Acids, Nonesterified; D008055:Lipids; D008894:Milk Proteins