Application of a new, simple and economic colorimetric method for the determination of non-esterified fatty acids in vegetable oils

The amount of non-esterified fatty acids in eight different vegetable oil samples has been determined by two different methods: (a) with a standard titration procedure, and (b) with a new colorimetric method which utilizes phenol red solubilized in reverse micelles. The results obtained by the two methods are in good agreement, although the standard deviation in the case of the phenol red method is significantly higher compared with the conventional titration. The main advantage of the new colorimetric method is an economic one: only small amounts of oil samples (less than 0·1 ml) are required and a comparably small amount of organic solvent (less than 5 ml isooctane) is needed.