Evaluation of Ethyl Caproate and Procyanidin in Beverages via Liposome Observation

Sake is a traditional Japanese alcoholic beverage that contains ethyl caproate (EC), a compound that enhances its economic value due to consumer preference. Procyanidins are polyphenolic compounds found in fruits such as apples, with procyanidin B2 (PB2) commonly used as a standard compound. Detecting EC and PB2 directly in intact or simply prepared beverages (e.g., dilution without organic solvent) requires liposomes as a model system. In this study, we focused on liquid-ordered/liquid-disordered liposomes, particularly reverse-domain liposomes, which were identified by fluorescence microscopy. EC and PB2 were found to increase and decrease the ratio of reverse-domain liposomes, respectively. The observation of cell-sized liposomes, combined with calibration curves, enabled a simplified analysis of EC and PB2. This approach has potential applications in the development, optimization, and practical implementation of food analytical methods for routine monitoring of beverage quality. These findings also provide a foundation for further studies on the biophysical and physiological properties of EC and PB2.