Daily Monitoring of Ripening Processes of a Tomato Using an Original Handheld Visible–Near-Infrared Spectrometer

Abstract

A handheld visible- and shortwave near-infrared spectrometer has been developed for monitoring daily changes in fruits and vegetables. The ripening processes of a mini tomato sample have been monitored daily for about 100 days by this instrument and color values L*a*b* and Brix were measured. Obtained reflection spectra in the 400–1050 nm range were converted to absorption spectra and daily changes of band areas of chlorophyll a (Ch1 a; 640–710 nm), carotenoids (460–520 nm), lycopene (545–600 nm), and water + sugar (920–1050 nm) were determined. The band area of lycopene increased rapidly from 36 to 44 days associated with the increase in a* value, indicating that the increase in the reddish color originated from the increase of lycopene. On the other hand, the band area of Chl a decreased exponentially over 100 days. This Chl a decrease could be well fitted by the first-order reaction giving the rate constant k = 4.07 × 10–7 s–1. These quantitative daily changes of pigments in fruits and vegetables are expected to provide comprehensive bases for their cultivation and harvest.