Photonic detection of ethanol dynamics in climacteric fruits using CO2 laser-based photoacoustic spectroscopy

This study investigates the use of CO 2 laser photoacoustic spectroscopy (CO 2 LPAS) for non-destructive monitoring of ethanol released during post-harvest ripening of Hachiya kaki fruits. Individual fruits were examined over six weeks under ambient conditions. Ethanol signals were low in the initial phase and showed marked increases around weeks 3–4, reaching maximum values of 34.78 ppm, accompanying enhanced weight loss and softening. The temporal profiles and the Ethanol-to-Weight Index (EWI) indicated distinct metabolic responses among the fruits, reflecting the shift from aerobic to anaerobic pathways and subsequent tissue degradation. The results demonstrate that CO 2 LPAS can sensitively track volatile metabolic markers and offers a practical approach for assessing ripening stage and early spoilage in climacteric fruits.