Alleviation of harmful effects of prolong storage at low temperature in harvested pomegranate fruit by exogenous proline

The effect of exogenous administration of two concentrations of proline (10 and 20 mM) on postharvest values and chilling injury (CI) of ‘Malaseh Saveh’ pomegranate (Punica granatum L.) fruits was investigated during 90 days at 4 °C. Proline treatment attenuated CI symptoms and prevented membrane lipids peroxidation, and reduction of cell membrane integrity in treated fruits, which were represented by malondialdehyde and electrolyte leakage, respectively. Therewith, a higher amount of endogenous proline (352.48 µg g⁻¹ FW) was perceived in 20 mM proline-treated fruits at the end of the cold storage time. Furthermore, proline treatment increased antioxidant capacity and antioxidant enzyme activity, namely ascorbate peroxidase, superoxide dismutase, and catalase, and also retained ascorbic acid amount at higher levels. This treatment decreased the activity of polyphenol oxidase and enhanced the phenylalanine ammonia-lyase activity which led to high accumulation of total phenol, flavonoids, and anthocyanin. All in all, exogenous application of proline, especially 20 mM concentration, as a safe, natural, and environment-friendly osmolyte substance, could alleviate harmful effects of CI and retain eating values of pomegranate fruits all over long-term postharvest and shelf life.