Abstract
Lipolytic activities of 60 samples of human milk obtained from 21 mothers at 5 to 155 days after parturition were determined. The activity was extensively stimulated by addition of 1.0 to 10.0mg of bile acids such as cholic acid, deoxycholic acid and taurocholic acid to 1.0ml of human milk. In the presence of 5.0μmoles (2.0mg) of cholic acid, 36.1±5.0μmoles of free fatty acids were liberated from 1.0ml of human milk at pH 8.0 after 120 minutes incubation at 37°C; the hydrolysis ratio of the fat was 33.9±7.2%. On the other hand, without cholic acid, the amount of liberated free fatty acids was only 4.3±3.2μmoles and the hydrolysis ratio was 3.9±3.2%. The activity observed in the presence of cholic acid was negatively correlated with the stage of lactation (r=-0.437, p<0.01) and positively with fat (r=0.595, p<0.01) and nitregen (r=0.541, p<0.01) contents of human milk.
In the presence of cholic acid, human milk lipase showed the maximum activity between pH 7.8 and 8.8. It was comparatively active under acid conditions even at pH 4.0 but was almost inactive above pH 9.5. It was completely inactivated by heating at 55°C and 60°C for 10 minutes and 2 minutes, respectively.
