Food Chemistry 39 (1991) 249-256 Application of a New, Simple and Economic Colorimetric Method for the Determination of Non-esterified Fatty Acids in Vegetable Oils Peter Walde & Claudio Nastruzzi Institut fiir Polymere, Eidgen6ssischeTechnische Hochschule, Universit~itstrasse 6, CH-8092 Ziirich, Switzerland (Received 2 February 1990; accepted 23 April 1990) ABSTRACT 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. INTRODUCTION The content of free (non-esterified) fatty acids in vegetable oils is usually determined by titration with standard alkali by using, for each measure- ment, 10 g oil in 50 ml of a solvent consisting of equal volumes of ethanol and diethyl ether (Gunstone et al., 1986). Recently, a new colorimetric titration method for the determination of the concentration of non-esterified fatty acids in vegetable oils has been described (Walde, 1990). This method uses reverse micellar solutions and takes advantage of their optical transparency and of their solubilization capacity for water-insoluble as well as for water-soluble compounds. 249 Food Chemistry 0308-8146/90/$03"50 © 1990 Elsevier Science Publishers Ltd, England, Printed in Great Britain