Within-day variation of taurine and other nitrogen substances in human milk

Milk samples were collected from seven mothers during their 8th wk of lactation. On the day of collection one breast was completely emptied at 600, 1000, 1400, 1800, and 2200 h. Concentrations of total nitrogen, protein nitrogen, urea nitrogen, and free amino acids (taurine and glutamine plus glutamic acid) were determined. Concentrations of these nitrogen substances in the milk differed significantly among women but were relatively constant during the day. The mean concentrations of these substances per 100 ml of milk were total nitrogen, .189 g; protein nitrogen, .145 g; urea nitrogen, .020 g; taurine 34.9 mumol; glutamine plus glutamic acid, 200.0 mumol.