Investigating the Carotenogenesis Process in Papaya Fruits during Maturity and Ripening by Non-Destructive Spectroscopic Probes

Climacteric fruits such as papaya are characterized by changes in the pigment composition during fruit ripening. Therefore, information on the degree of fruit ripeness with respect to the pigment composition using proper monitoring tools is important to growers for determining the appropriate harvest time associated with best quality. This study is aimed at exploring the applicability of spectroscopic probes such as laser-induced fluorescence (LIF) and confocal Raman microspectroscopy for the nondestructive, extraction free and rapid evaluation of pigment changes associated with the growth and ripening of papaya fruits. The laser-induced fluorescence spectra of the papaya show that as the fruit ripening progresses, there is a decrease in intensity of the chlorophyll bands with a simultaneous increase in intensity of carotenoid bands. This phenomenon can be regarded as a characteristic feature of the ripening of papaya. To obtain additional insight about the carotenoid dynamics during ripening, confocal Raman microspectroscopy has been utilized. The Raman spectra show strong spectral signature of carotenoids in both pericarp and mesocarp whose intensity increases as the fruit ripens. In addition, the bands of carotenoids are more prominent in the spectra of the mesocarp than in the pericarp. These facts are supported by the quantitative estimation of pigments in the papaya fruits by ultraviolet-visible spectroscopy. The determined spectral signatures can be used as indices for effective monitoring of ripening of fruits and commercial application for the phenotyping of important plant parts, screening, grading, shelf life estimation and quality standardization.