INFLUENCE OF THE DERIVATIZATION PROCEDURE ON THE RESULTS OF THE GASCHROMATOGRAPHIC FATTY-ACID ANALYSIS OF HUMAN-MILK AND INFANT FORMULAS

Many different analytical procedures for fatty acid analysis of infant formulae and human milk are described. The objective was to study pos sible pitfalls in the use of different acid-catalyzed procedures compa red to a base-catalyzed procedure based on sodium-methoxide in methano l. The influence of the different methods on the relative fatty acid c omposition (wt% of total fatty acids) and the total fatty acid recover y rate (expressed as % of total lipids) was studied in two experimenta l LCP-containing formulae and a human milk sample. MeOH/HCl-procedures were found to result in an incomplete transesterification of triglyce rides, if an additional unpolar solvent like toluene or hexane is not added and a water-free preparation is not guaranteed. In infant formul ae the low transesterification of triglycerides (up to only 37 %) coul d result in an 100 %-overestimation of the relative amount of LCP, if these fatty acids primarily derive from phospholipids. This is the cas e in infant formulae containing egg lipids as raw materials. In formul a containing fish oils and in human milk the efficacy of esterificatio n results in incorrect absolute amounts of fatty acids, but has no rem arkable effect on the relative fatty acid distribution. This is due to the fact that in these samples LCP are primarily bound to triglycerid es. Furthermore, in formulae based on butterfat the derivatization pro cedure should be designed in such a way that losses of short-chain fat ty acids due to evaporation steps can be avoided. The procedure based on sodium methoxide was found to result in a satisfactory (about 90 %) conversion of formula lipids and a reliable content of all individual fatty acids. Due to a possibly high amount of free fatty acids in hum an milk, which are not methylated by sodium-methoxide, caution is expr essed about the use of this reagent for fatty acid analysis of mothers milk. It is concluded that accurate fatty acid analysis of infant for mulae and human milk requires a careful and quantitative derivatizatio n of both polar and unpolar lipid classes. Sodium methoxide seems to b e a reliable and time-saving method for routine fatty acid analysis of infant formulae, which should be validated by interlaboratory compari son. Anhydrous procedures based on methanolic hydrogen chloride includ ing an additional unpolar solvent are also suitable for infant formula e but seem to be preferable for human milk samples.