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Convenient Method to Determine Free Fatty Acid of Rice Using Thin-Layer Chromatography and Flame-Ionization Detection System¹

¹Study supported in part by a grant-in-aid for a research program “Integrated Studies of New Rice Production Technology by Breeding Superior Varieties for the Next Millennium” provided by the Ministry of Agriculture, Forestry and Fisheries (MAFF), Japan. ²Kyushu National Agricultural Experiment Station, Ministry of Agriculture, Forestry and Fisheries, Nishigoshi, Kumamoto 861-1192, Japan. ³Corresponding author. Fax: +81-96-249-1002 E-mail: nishiba@knaes.affrc.go.jp

A convenient method which possessed simplicity and high sensitivity was designed to investigate the changes in free fatty acid (FFA) of rice during storage using a thin-layer chromatography and flame-ionization detection (TLC/FID) system. In this method, two different solvent systems for TLC were used according to the purpose of experiments. Solvent system A (hexane and diethyl ether and acetic acid 80:20:1) was suitable to obtain a chromatogram showing the overall state of rice lipid degradation. Using solvent system A, the degradation of triglyceride or the increase in FFA during storage was clearly visualized as changes in the chromatogram. Solvent system B (hexane and acetic acid 100:1) was used to improve the low reproducibility of the TLC/FID method. When methyl stearate was used as an internal standard with solvent system B, high reproducibility of the FFA value was obtained, and very small changes were detectable in stored white milled rice. This method has small sample size and simple operation and is more sensitive than the standard titration method. Therefore, this seems to be an especially convenient method for small-scale storage tests or for experiments using many samples.