A Highly Sensitive Method for the Analysis of Long-Chain Free Fatty Acids in Yogurt by High Performance Liquid Chromatography with Fluorimetric Detection

The fat content in food is concerned by genera l public, because over uptake of some saturated fatty acids could lead to heart related disease. Therefore, practical method for the analysis of fatty acids in food is essential. In this article, a highly sensitive HPLC method is described for the quantitative analysis of long-chain free fatty acids in yogurt, including lauric, myristic, palmitic, stearic, palmitoleic, oleic and linoleic acids. The fatty acids were labeled with a fluorophore by reacting with 2-(2-naphthoxy) ethyl 2-(piperidino) ethanesulfonate (NOEPES) at 95℃ for 0.5 h in the presence of 18-crown-6 and solid potassium carbonate. The resulting naphthoxyethyl derivatives were separated on a C8 column with a mobile phase of methanol-water (92:8, v/v) and detected fluorimetrically (excitation at 235 nm and detection at 350 nm). Before labeling, the fatty acids in yogurt were extracted with toluene and the resulting toluene extract was directly subject to the labeling without time-consuming steps of solvent evaporation and solvent replacement. The fluorimetric HPLC analysis of fatty acids could be measured at few μ M levels in yogurt. The results indicate that the content of free fatty acids in low-fat yogurt is lower than that in plain yogurt from the same food producer.