ESTIMATES OF CONSERVATION OF 2-PALMITIC ACID DURING DIGESTION AND ABSORPTION OF HUMAN MILK BY BREAST-FED INFANTS. ▴ 1880

Human milk fatty acids contain 20-25% palmitic acid (16:0) with about 70% of the 16:0 esterified at the sn-2 (center) position of the triglyceride (TG). Endogenous lipases hydrolyse fatty acids from the TG 1,3, but not sn-2 position, to give 2-monoglycerides(MG) and unesterified fatty acids. The positioning of 16:0 at the 2 position of human milk TG may facilitate 16:0 absorption as a 2-MG; unesterified 16:0 tends to form insoluble soaps with minerals, eg Ca²⁺, Mg²⁺ the intestine. However, the milk enzyme bile salt stimulated lipase can hydrolyze milk TG to glycerol and unesterified fatty acids in vitro. Thus, the pathway for absorption of 16:0 (2-MG or free fatty acid) is uncertain. These studies, therefore, compared the enrichment of 16:0 at the sn-2 position of the plasma chylomicron (CM) TG from full-term infants who were exclusively breast-fed or fed formula with synthesized TG (Betapol) containing 22% 16:0 with 31% 16:0 in sn-2 fatty acids, to 4 mths of age. Blood (3mL) was collected and CM isolated from plasma at d = 1.006g/mL by ultra-centrifugation(2 hours, 435,000g). Lipids were extracted, TG purified and 2-MG prepared using pancreatic lipase. TG and 2-MG fatty acids were analyzed by capillary GLC. Infants fed formula with Betapol had 15.0% and breast-fed infants had 26.3% 16:0 in the CM TG sn-2 fatty acids. As the formula contained no bile salt stimulated lipase, the enrichment of 16:0 at the sn-2 position indicates the monoacylglycerol pathway (re-esterification of absorbed 2 MG) accounted for synthesis of 50% of the CM TG. The recovery ofsn-2 16:0 in the CM TG of breast-fed infants was also 50% of the amount in the milk. This suggests 16:0 is not quantitatively released from the 2 position of human milk, in vivo, in breast-fed infants. Supported by MRC Canada.