Modeling Tomato Ripening Based on Carotenoid Raman Spectroscopy: Experimental Versus Kinetic Model

This work reports on a combined experimental and theoretical investigation on the carotenoid Raman signal in several tomato fruits during their postharvest time evolution and ripening. Both resonant (180°) backscattering and polarized (90°) Raman scattering were used to monitor the most prominent bands of carotenoid (lycopene and β-carotene) evolution in different tomato varieties. Relevant findings of the present investigations were that while the depolarization ratio of the ν₁ band hardly changed with time, the Raman ν₁ band intensity did change showing a similar pattern for all tomatoes investigated. Indeed, all cases investigated revealed a rise of the carotenoid signal coincident with the onset of the turning stage of the fruit ripening, a pronounced maximum of the Raman signal followed by a post-maximum decline at the red ripening stage. A kinetic model has been developed to describe the time evolution of the observed Raman signatures based on the rate coefficient of the carotenoid synthesis and the time evolution of the scattering coefficient of the fruit. The model describes satisfactorily the tomato evolution through the distinct ripening stages providing new insight on the assessment of the postharvest fruit control and quality.