EVALUATION BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY OF THE HYDROLYSIS OF HUMAN-MILK TRIACYLGLYCERIDES DURING STORAGE AT LOW-TEMPERATURES

The effect of various storage methods on the stability of the triacylg lyceride fraction of human milk was evaluated. Samples were treated as follows: Group I - stored at -20 degrees C for 4 months, group II - h eated for 1.5 min at 80 degrees C and stored at -20 degrees C for 4 mo nths, group III - stored at -80 degrees C for 4 months and thawed rapi dly at room temperature (25 degrees C) just before analysis and group IV - stored at -80 degrees C for 2 months, thawed rapidly at room temp erature (25 degrees C), then stored at -80 degrees C for a further 2 m onths and finally thawed rapidly at 25 degrees C just before analysis. The absence of hydrolysis products in group II and group III indicate d that these storage procedures were satisfactory even when samples we re rapidly thawed for a short time (group IV). Only storage at -20 deg rees C without previous heat treatment led to the hydrolysis of triacy lglycerides and the appearance of free fatty acids (group I). On the o ther hand, the effect that freezing and thawing had over the lipolysis grade was studied. Samples were treated as follows: group V - stored at -20 degrees C for 2 months, thawed slowly at refrigerator temperatu re (5 degrees C), held at this temperature for one week and stored for a further month at -20 degrees C. Freezing and thawing activated lipo lysis and increased the production of free fatty acids, monoacylglycer ides and diacylglycerides. Milk samples were analyzed by reversed-phas e HPLC with a ternary gradient of acetonitrile-dichloromethane-acetone and an evaporative Light-scattering detector. (C) 1998 Elsevier Scien ce B.V. All rights reserved.