Gastric lipase, pancreatic colipase-dependent lipase, and bile salt-stimulated lipase all have potential roles in digestion of human milk triacylglycerol. To reveal the function of each lipase, an in vitro study was carried out with purified lipases and cofactors, and with human milk as substrate. Conditions were chosen to resemble those of the physiologic environment in the gastrointestinal tract of breast-fed infants. Gastric lipase was unique in its ability to initiate hydrolysis of milk triacylglycerol. Activated bile salt-stimulated lipase could not on its own hydrolyze native milk fat globule triacylglycerol, whereas a limited hydrolysis by gastric lipase triggered hydrolysis by bile salt-stimulated lipase.Gastric lipase and colipase-dependent lipase, in combination, hydrolyzed about two thirds of total ester bonds, with monoacylglycerol and fatty acids being the end products. Addition of bile salt-stimulated lipase resulted in hydrolysis also of monoacylglycerol. When acting together with colipase-dependent lipase, bile salt-stimulated lipase contributed also to digestion of tri-and diacylglycerol. We conclude that digestion of human milk triacylglycerol depends on three lipases with unique, only partly overlapping, functions. Their concerted action results in complete digestion with free glycerol and fatty acids as final products. (J.

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From an energetic point of view fat is the main nutrient during early infancy. Triglyceride (triacylglycerol) constitutes more than 95 % of the dietary fat and provides about half the energy in the diet of the milk fed infant. Each triglyceride molecule consists of three fatty acids esterified to one molecule of glycerol. Since greater than hundred individual fatty acids have been detected in human milk it is evident that not only the molecular structure but also the nutritional value may differ considerably between species of milk triglycerides (1). With this view in perspective it is noteworthy that current guidelines on infant nutrition give only few detailed recommendations on advisable amount and composition of fat in infant formulas for term an preterm infants. This reflects that available data in infants on qualitative and quantitative requirements of various lipid components are scanty.On the other hand it is reasonable to assume for lipids as well as other nutrients that the amount and composition of human milk is ideal to cover the needs of the newborn infant. Hence, current recommendations are based more on knowledge of the fat content and composition of human milk than on reliable data on requirements ( 2 ) . A drawback is however that even from formulas with a fatty acid composition very similar to human milk the coefficient of fat absorption is much lower than from raw milk, particularly in preterm infants. Moreover, calculated on individual fatty acids this difference in utilization is more pronounced for some fatty acid species than for others (3). From an increasing awareness that lipids serve other functions than being merely a source of exchangeable energy (4) it is obvious that future recommendations on fat composition of infant formulas must be based on more detailed data on requirements as well as on an understanding of the reasons behind the difference in utilization of fat from human milk compared to infant formulas. Before these reasons will be fully understood it is necessary to reveal the exact mechanisms of the digestion and absorption of milk triglyceride in the breast-fed infant.

A pregastric lipase was purified from calf pharyngeal tissues. The purification procedure was based on chromatographies on octyl-Sepharose and lentil-lectin-Sepharose followed by gel filtration. The final preparation, with an overall recovery of 26% of activity, gave a single protein band on dodecyl sulfate/polyacrylamide gel electrophoresis with a M , of 55000. The M , on gel filtration was 44-48000. The discrepancy may be due to the fact that pregastric lipase is a glycoprotein containing z 10% (w/w) of carbohydrate. The PI was around 7.0 and the enzyme protein is characterized by a high content of branched, aliphatic amino acid residues. The NH2-terminal amino acid sequence is : H2N-Phe-Leu/(Ile)-Gly-. Rabbit antibodies to the purified preparation detected only one component in the crude starting material in immuno-blotting experiments. Preincubation with antiserum resulted in loss of enzyme activity, showing that the antibodies were directed against the lipase.

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