Biochemistry of maternal milk in early lactation

The analysis of more than 550 human milk samples showed that triglycerides (accounting for 96-99 per cent of the total lipids) increased from 2 to 3.5 g/100 ml mainly during the first week postpartum and remained constant thereafter. In contrast, both cholesterol and vitamin E concentrations decreased from 35 to 20 mg/100 ml and from 1.7 to 0.30 mg/100 ml, respectively. The phospholipids remained constant (40 mg/100 ml). The fatty acid composition of total lipids showed remarkable changes. Mid-chain fatty acids (C10, C12, C14) increased, whereas the long-chain polyunsaturated fatty acids decreased. The P/S ratio of 0.32 remained constant throughout lactation. The mean protein content of human milk decreased from approximately 2 g/100 ml at day 2 to approximately 1 g/100 ml at day 36 of lactation. The content of each individual amino acid decreased likewise. However, when we expressed the amino acid values in relation to the protein value--that is as gram of amino acid per gram of protein--some decreased, some remained constant and some increased indicating a changing protein pattern. Throughout the whole period of investigation, non-protein nitrogen accounted for about 20 per cent of total nitrogen, taurine ranging at about 6 mg/100 ml. The calcium content increased from a mean value of 25 mg/100 ml at day 1 to 32 mg/100 ml at day 5 and remained constant at 30 mg/100 ml up to day 36. The mean phosphorus content increased from 10 mg/100 ml at day 1 to 17 mg/100 ml at day 8 and then continuously decreased to 13 mg/100 ml at day 36.