Diurnal and Within-Feed Variations in Lipase Activity and Triglyceride Content of Human Milk

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Abstract
This study examined the diurnal and within feed variations in the two lipases of human milk, bile-salt-stimulated lipase (BSSL) and lipoprotein lipase (LPL). In addition, all milks were also analyzed for triglyceride content. As compared to BSSL, LPL activity was more variable both among mothers and among different samples from the same mother (largest variation, 0-2.8 U/ml milk). The only significant variation in lipase activity was in LPL activity during a 24-h period (0.96 .+-. 0.113, 0.52 .+-. 0.21, and 0.57 .+-. 0.092 U/ml milk at 0801-1600, 0001-0800, and 1601-2400 h, respectively) (p < 0.05). Triglyceride content showed no significant diurnal variation but did increase significantly during a single feeding (31 .+-. 9.4, 52 .+-. 11.7, and 72 .+-. 14.8, .mu.moles triglyceride/ml milk for fore-, mid-, and hind-milks, respectively) (p < 0.05). There was no correlation between either LPL or BSSL activity and triglyceride content of the milks. Our data indicate that milk obtained for banking or research purposes will contain similar levels of BSSL activity irrespective of diurnal or within-feed timing of milk collections.