P6: Simple method for the simultaneous quantification of medium-chain fatty acids and ethyl hexanoate in alcoholic beverages by GC–FID

Free medium-chain fatty acids (MCFAs) can negatively influence the fermentation process and taste quality in alcoholic beverages.  Ethyl hexanoate, an ethyl ester of hexanoic acid, is important in providing a fruit-like flavour to drinks, particularly in Japanese sake.  It is imperative to control the concentrations of MCFAs and its esters for the production of high-quality alcoholic beverages; therefore, a suitable analytical method is desirable for the quantification of these organoleptic compounds.  In this study, we developed a direct injection method for a gas chromatography–flame ionized detector following the semi-purification of chemical components including esters, alcohols and MCFAs in alcoholic beverages.  Evaluation of MCFAs by this method gave limit of detection on the order of sub-ppm and relative standard deviation values that are less than 10% of the values demonstrated in standard solution.  Good repeatability and recovery against MCFAs and ethyl hexanoate were also obtained in non-distilled real alcoholic beverages.  As this method enabled us to quantify the concentrations of MCFAs and ethyl hexanoate simultaneously, the proportion of ester against MCFAs was proposed as a quality control index. This method is ideal for routine analysis in the alcohol beverage industry.