Biofluorometric Gas-Imaging System for Evaluating the Ripening Stages of “La France” Pear Based on Ethanol Vapor Emitted via the Epicarp

Fruits can emit ethanol, which is generated through fermentation during hypoxic storage. We imaged spatiotemporal changes in the gaseous ethanol emitted by "La France" pear via its epicarp. The gas-imaging system utilized enzymes to transduce the ethanol concentration into fluorescence intensity. Initially, the uniformity of the enzyme and coenzyme distribution was evaluated to validate the imaging capability. Subsequently, two surface-fitting methods were compared to accurately image ethanol emitted from three-dimensional (3D) objects with a double-curved surface. The imaging results of ethanol emitted from the pear indicated that the distribution of ethanol was related to lenticels, which have been reported to possess high ethanol diffusivity, on the epicarp. As quantified by the system (uniformity of coenzyme and enzymes was 93.2 and 98.8%, respectively; dynamic range was 0.01–100 ppm), ethanol concentration increased with the storage period under hypoxic conditions (0.4–5.3 ppm, from day 1 to 10). The system enables the observation of the location, quantity, and temporal pattern of ethanol release from fruit, which could be a useful technology for agricultural applications.