RESUMEN
Large-scale food fortification of vegetable oils with vitamin A has been implemented successfully for decades in numerous African and Asian countries, contributing demonstrably to reductions in vitamin A deficiency. For these programmes, reliable and validated analytical data are essential to demonstrate compliance with legal standards and fortification levels. Commonly, many analytical laboratories use a saponification method for the quantitative analysis of retinyl palmitate (the mostly used form of vitamin A for fortification) in fortified oils, which implies a multiple-step procedure with long analysis times and the potential risk of analyte loss. The aim of the present study was to develop and validate a direct High-performance Liquid Chromatography (HPLC) method that reduces these sample preparation steps, leading to the cost- and time-efficient quantification of retinyl palmitate in fortified oils. Oil samples are dissolved into the HPLC solvents, then injected directly into a common C18 column, and subsequently detected by a fluorescence detector. The limit of quantification (1.0 mg retinyl palmitate kg-1) and the working range of 1.0-100 mg retinyl palmitate kg-1 with a linearity of R2 = 0.9989 are appropriate to analyse fortified oil samples. The method also showed adequate precision (RSD between 1.1% and 3.1%) and recoveries (86-103%) at two different concentration levels. The accuracy of the direct HPLC method was additionally proven by the comparison of spiked samples with two external laboratories that used the saponification method. The robustness of the method was confirmed by the analysis of various spiked edible oils. The HPLC column is not deteriorated by the lipid matrix and shows excellent stability and long lifetime. Also, 9-cis-retinyl palmitate formed mainly by light exposure could be detected by this method. The direct HPLC method is a well-suited alternative to the saponification method for the rapid and reliable routine analysis of fortified oil samples.