Contribution of Sulfate and Sulfoesters to Total Sulfur Intake in Infants Fed Human Milk

Colostrum (d 2-4) and mature human milk samples (d 23-30) collected from eight mothers giving birth at 31 +/- 7 wk of gestation were analyzed for total sulfur, free inorganic sulfate and acid labile sulfoesters. The data presented are representative of complete 24-h expressions. Total sulfur was measured using a wet digestion procedure in which all forms of sulfur were converted to inorganic sulfate. The sulfate was quantified by a radiometric barium precipitation assay. Total sulfur showed no marked diurnal variation, but the mean concentration in 19 colostrum samples (10.2 +/- 4.2 mmol/L) was significantly higher than in 14 mature milk samples (4.3 +/- 0.8 mmol/L) (P less than 0.001). The range of predicted 24-h intakes of sulfur by infants fed colostrum (0.78-3.22 mmol/kg body weight) was slightly higher than those fed mature milk (0.54-1.06 mmol/kg), but it was not significantly different. The combined fractions of free inorganic sulfate and acid-labile sulfoester fractions contribute less than 5% to the total sulfur content of either colostrum or mature milk. However, the physiological significance of these milk components remains to be determined.