Calcium chloride postharvest treatment delays the ripening and softening of papaya fruit

Papaya fruits ripen and deteriorate rapidly after harvest. It is well established that the calcium treatment delays fruit ripening. However, the regulation of fruit ripening by calcium treatment in papaya remains unclear. In the present study, we investigate the effect of calcium chloride treatment (2.5% CaCl2 solution immersion for 15 min), which significantly delayed the ripening of papaya fruit. Fruit yellowing was delayed by 4 days in CaCl2-treated fruits compared with control. CaCl2 treatment significantly delayed loss in fruit firmness and an increase in the total soluble solid content, relative conductivity, and ethylene peak, as well as reduced ethylene production. It inhibited the activity of cell wall degrading enzymes and the expression of cell wall softening-related genes and ethylene signal pathway-related genes. These findings indicate that the CaCl2 treatment delays the ripening and softening of papaya fruits by inhibiting the expression of enzymes and genes related to cell wall degradation and ethylene signal transduction. Practical applications Papaya is an economically important fruit crop cultivated worldwide. These fruits ripen and deteriorate rapidly after harvest. Calcium chloride treatment (2.5% CaCl2 solution immersion for 15 min) studied in the present study significantly delayed the ripening of papaya fruit. The calcium treatment is easy to operate and control and is effective in maintaining fruit quality and reducing postharvest losses of papaya. It is a safe and non-toxic alternative to chemical treatment for fruit storage and transportation.