Quality attributes, pectolytic enzyme activities and physiological changes during postharvest ripening of nectarine

The postharvest ripening at 20C and 90-95% RH for 10 days of 'Armking' nectarine grown in a greenhouse was investigated over two seasons. Firmness, titratable acidify, ascorbic acid, pH and maturity index were all adequate to stablish the rate of ripening. However, soluble solids content and reducing and non-reducing sugars showed no significant changes. It took about 10 days for very early ripening fruit (100 g weight and 82 N firmness) and 6 days for normal early ripening fruits (115 g weight and 46 N firmness), both harvested at preclimacteric stage, to become eating ripe (near 20 N). Total weight loss and decay after 10 days was approximately 11%. During ripening there was a temporal coincidence among higher rates of ethylene production, higher pectinmethylesterase (PME) and polygalacturonase (PG) activities, lower firmness and acidity and higher maturity index. PME and PG activities increased during ripening, with a highly negative linear correlation between activities of the two enzymes and firmness. In very early ripening fruit, PME activity was more closely related to softening than PG, whereas in normal early ripening fruit, PG activity was slightly more closely linked to the loss of firmness than PME.