Quantifying lycopene synthesis and chlorophyll breakdown in tomato fruit using remittance VIS spectroscopy

Abstract

The aim of this study was to increase the understanding of chlorophyll breakdown and lycopene synthesis at a quantitative level in Solanum lycopersicum fruit. To accomplish this, a kinetic model is proposed describing the transition from chloro- to chromoplast. Remittance VIS spectroscopy was used to assess chlorophyll and lycopene levels non-destructively in cocktail and round type tomatoes. Tomatoes were stored at constant temperatures between 4 and 24°C, or at a stepwise changing temperature between 4 and 16°C. Chlorophyll and lycopene levels were measured repeatedly over time and used to calibrate a kinetic model that describes how an autocatalytic enzyme system links chlorophyll breakdown to lycopene synthesis, including breakdown of lycopene precursor and lycopene itself. Increasing storage temperatures increased the reaction constant for lycopene synthesis more than that of chlorophyll breakdown for both tomato types. The reaction constants describing chlorophyll breakdown and lycopene synthesis were considerably larger, and the estimated enzyme levels lower for the round type. This allows round tomatoes to quickly resume lycopene synthesis after a cold storage period when enzyme levels are low. Lycopene breakdown was established for the round type while the cocktail type showed lycopene precursor breakdown. Chlorophyll breakdown and lycopene synthesis, as affected by storage temperature and tomato type, is covered well by the model for both tomato types. We hypothesise that the postulated enzyme system, responsible for the direct link between chlorophyll breakdown and lycopene synthesis, is due to STAY-GREEN proteins. Remittance VIS spectroscopy is, in combination with a parameter estimation tool, suited to screen tomato genotypes for intended colour transformation performance, or as tool in chloroplast to chromoplast transition studies.