EFFECTS OF CHILLING ON TOMATO FRUIT TEXTURE

The effects of chilling on tomato (Lycopersicon esculentum Mill cv. Caruso) texture were investigated using fruit stored at 22-degrees-C (nonchilled) or 5-degrees-C (chilled) for 28 days, or at 5-degrees-C for 15 days before transfer to 22-degrees-C to facilitate ripening during an additional 13 days (prechilled). Prechilled fruit exhibited symptoms of slight chilling injury, i.e. development of mealiness, accelerated softening relative to that of nonchilled fruit and nonuniform surface colour development. The firmness of all fruit decreased during ripening and chilled storage when measured by flat plate compression and puncture, especially during the early stages of ripening of nonchilled and prechilled fruit. The compression firmness of pericarp tissue similarly decreased during ripening of nonchilled and prechilled fruit, but was maintained during chilling. Total moisture content (ca 94%) of tissue, uronide content (32-35% w/w) and extracted beta-galactosidase activity did not differ significantly (P > 0.05) among fruit during ripening and chilled storage. The degree of uronide methyl esterification in ethanol-insoluble solids prepared from pericarp tissue (EIS) was relatively low for all fruit, i.e. < 40%. EIS from which greater levels of pectinesterase were extracted (i.e. nonchilled>chilled>prechilled) exhibited decreased levels of uronide methyl esterification. Markedly elevated levels of beta-glucosidase activity were extracted from prechilled EIS. Total polygalacturonase activity (mainly as PGI) and autolysis of enzyme-extracted EIS were inversely correlated (P less-than-or-equal-to 0.05) only with the loss of nonchilled fruit and tissue firmness and prechilled fruit firmness. Results suggest a possible role for beta-glucosidase in textural changes of prechilled fruit and tissue (e.g. loss of firmness, development of mealiness) and also implicate loss of skin strength in the softening of whole fruit during chilling.