Relationship between the firmness of Golden Delicious apples and the physicochemical characteristics of the fruits and their pectin during development and ripening.

Firmness at harvest determines the postharvest storability and quality of apples. The climate change has altered the physiological processes of fruits and the reliability of ripening indicators typically used to determine the harvest time, compromising fruit firmness. In this study, 'Golden Delicious' apples were harvested at several developmental/ripening stages (107, 122, 137, 152 and 167 days after full bloom, DAFB) and evaluated for physicochemical attributes, which were correlated with fruit firmness. The 167 DAFB fruit corresponded to fruit at the commercial harvest. Fruit harvested at 107 and 122 DAFB did not develop the characteristics of ripe fruit while fruit harvested after 137 DAFB ripened normally. Fruit at commercial harvest showed low firmness. The changes of fruit weight, diameter, height, tristimulus color (L* values) as well as the content of total soluble solids and moisture in fruit correlated well with fruit firmness (r values from -0.76 to -0.97). The changes of pectin content, degree of esterification, molecular weight and content of glucose and galactose in pectin showed a positive relationship with firmness (r = 0.62-0.94). The content of protein, galacturonic acid and mineral elements in pectin correlated negatively with firmness (r -0.66 to -0.99). The results demonstrated that commercial harvest was delayed 30 days, compromising fruit firmness. Some underestimated ripening indicators may help in determining the harvest time of apples.