A reassessment of heat treatment as a means of reducing chilling injury in tomato fruit

Abstract

Recent studies have indicated that heat treatment administered prior to chilling reduces the incidence and severity of chilling injury in tomato fruit and other plant organs. Partial ripening of tomato and other fruits has also been shown to reduce chilling sensitivity. To test the relative merits of these “treatments”, tomato fruit (cv. ‘Rutgers’) were harvested when mature-green, held 3 days at ripening or heat-stress temperature (20 or 38°C, respectively), chilled for 20 days at 5°C, and assessed for ripening and injury over 7 subsequent days at 20°C. Based on chromaticity ( a ∗ ) values, lycopene content, rates of CO 2 and ethylene evolution, and visible injury (pitting on shoulders), heat-treated (38°C) fruit sustained more chilling injury and ripened much more slowly than the partially-ripened (20°C) controls. Membrane lipids extracted from outer pericarp tissue from 0 day, 3 day control, and 3 day heat-treated fruits were also analyzed. Lipid changes after 3 days at 20°C were typical of early ripening, whereas several anomalous changes occurred during 3 days at 38°C, most notably, a drop in steryl esters, large increases in phospholipids and cerebrosides, and a decrease in fatty-acid unsaturation in galacto- and phospholipids. These results show that, under certain conditions, heat treatment of tomato fruit may not reduce chilling injury as effectively as partial ripening.