Changes in cholesteryl esters of human milk with total milk lipid.

Twenty-five milk samples with a wide range of total lipid and degree of fatty acid saturation were chosen for this study. The milk samples were analyzed for total lipid, total cholesterol, and free cholesterol. The cholesteryl esters and triacylglycerols in these samples also were isolated and the fatty acids associated with each lipid class determined. Total cholesterol averaged 13.5 +/- 3.1 mg/dl of milk and was significantly correlated (r = 0.60, p less than 0.05) with total lipid. Free cholesterol averaged 10.9 +/- 2.3 mg/dl of milk and also was significantly correlated (r = 0.72, p less than 0.05) with total lipid. As total milk lipid increased, the fatty acids in cholesteryl esters became more saturated. The fatty acids most affected were 18:2 and 20:4. Total milk lipid and 18:2 in cholesteryl esters were inversely related (r = -0.49, p less than 0.05). There was also a negative correlation (r = -0.51, p less than 0.05) between 20:4 in cholesteryl esters and total lipid. The fatty acids in triacylglycerol were not correlated with total lipid. From these results it appears that the fatty acids esterified to cholesterol and triacylglycerol in milk may be drawn from different substrate pools.