Non-Destructive Monitoring of the Ripening of Plums Using Confocal Micro-Raman and Laser Induced Fluorescence Spectroscopy

Plums are nutraceutically rich and have health-promoting properties. To produce high-quality fruits, it is important to monitor them at harvest. This study illustrates the potential of nondestructive laser-induced fluorescence and confocal micro Raman spectroscopy for monitoring the ripening of plums. The fluorescence profile indicates that as fruit ripens, the intensity of the fluorescence of chlorophyll at 685 and 730 nm decreases with increase in the intensity ratio (F-685/F-730) of these bands. These observations reveal that as fruit ripens, there is a gradual loss of chlorophyll. In order to get further insight into pigment dynamics, the Raman spectra of the fruit were analyzed. The Raman spectra of pre and post-ripe stages of fruits show that as the fruit ripens, there is a prominent increase in the intensity of anthocyanin bands accompanied by subsequent decrease in the intensity of the carotenoid bands. The spectral analysis reveals that the ripening is associated with a decrease in the chlorophyll and carotenoid content with subsequent increase in anthocyanins. The results of this study highlight the utility of laser-induced fluorescence and confocal micro-Raman spectroscopy for the rapid, sensitive, and nondestructive monitoring of plum ripening.