Investigation of short-term variations in casein and whey proteins in breast milk of term mothers.
OBJECTIVE
We investigated changes in breast milk whey and casein proteins, between fore and hind milk during breast expression, between breasts and within 24-hour period during breast-feeding. This has implications for developing an appropriate sampling protocol for investigating the influence of milk composition on gastric emptying and infants' feeding behaviour.


METHODS
Breast milk samples were collected from mothers (n = 25) of healthy term infants ages 1 to 8 months. A total of 17 mothers provided fore and hind milk samples, which were collected during simultaneous expression of both breasts. Fifteen mothers provided samples from each breast-feed during 24-hour period, of which samples were selected from 4 time points (morning, day, evening, night). Whey and casein were isolated from skim milk, and protein concentration of the skim, whey, and casein fractions were determined.


RESULTS
Mean protein concentrations were found to be 13.5 ± 2.1 (skim milk), 7.6 ± 1.5 (whey), and 3.4 ± 0.97 g/L (casein). Protein concentrations were not significantly different between fore and hind milk. During a 24-hour period, no significant differences were found in protein concentration of any fraction at the 4 time points or between left and right breasts. Large variations were seen between mothers with coefficient of variances of 15.5%, 19.8%, and 28.4% for skim milk, whey, and casein, respectively.


CONCLUSIONS
Although there was wide variation between mothers, the small variations within mothers indicate that for sampling purposes, a single breast milk sample (fore or hind from each breast at any time point of the day) will be representative of that mother's protein concentration of skim, whey, and casein fractions for that day.
School of Chemistry and Biochemistry, University of Western Australia, Crawley, Western Australia, Australia. khans01@student.uwa.edu.au
Sadaf
S
Khan
Ylenia S
YS
Casadio
Ching T
CT
Lai
Danielle K
DK
Prime
Anna R
AR
Hepworth
Naomi J
NJ
Trengove
Peter E
PE
Hartmann
D000328:Adult; D001940:Breast / Q000378:metabolism*; D001942:Breast Feeding; D002364:Caseins / Q000378:metabolism*; D005247:Feeding Behavior; D005260:Female; D005746:Gastric Emptying; D006801:Humans; D007223:Infant; D007774:Lactation; D008297:Male; D008894:Milk Proteins / Q000378:metabolism*; D008895:Milk, Human / Q000378:metabolism*; D009035:Mothers; D047929:Term Birth; D000067816:Whey Proteins
D002364:Caseins; D008894:Milk Proteins; D000067816:Whey Proteins