Effects of human milk pasteurization and sterilization on available fat content and fatty acid composition

Background: Human milk is frequently heat treated in hospitals to reduce bacterial contamination, particularly in banked milk fed to preterm infants. Pasteurization and sterilization may induce oxidative losses of unsaturated lipids and vitamins and may inactivate enzymes and immunologic factors. This study was designed to examine the effects of pasteurization and sterilization on milk fat content available to the recipient infant and on fatty acid composition. Methods: In fresh, pasteurized (62.5 degrees C for 30 minutes), and sterilized (120 degrees C for 30 minutes) milk samples (5 mi) of 12 mothers (days 5-35 of lactation), fat content was determined gravimetrically and the contribution of 30 fatty acids was determined by gas-liquid chromatography. Results: The coefficients of variation for measurements of milk fat content were 0.7% and of fatty acids accounting for more than 0.09% of weight, 0.1-3.0%. Available fat content was 3.1 +/- 1.4 g/dl (mean +/- SD) in fresh human milk and 3.1 +/- 1.4 g/dl (not significant) in pasteurized human milk. Fat content declined to 2.7 +/- 1.1 g/dl (p < 0.001 vs. fresh) in sterilized human milk, because of increased fat adherence to the container surface after sterilization. The percentage composition of saturated, monounsaturated, and polyunsaturated fatty acids of the n-6 (C18:3, C20:2, C20:3, and C22:4) and the n-3 series (C18:3 C20:5, C22:5, and C22:6) was not affected by thermal treatment. Milk sterilization caused a slight decrease of linoleic (-0.7% vs. fresh milk; p = 0,006) and arachidonic (-2,6%, p = 0.045) acids. Conclusions: Pasteurization of human milk does not influence fat content and composition, but sterilization may reduce available fat content by more than 10%, whereas there are only slight changes in fatty acid composition.