Effect of sodium nitroprusside on biochemical and antioxidant properties of medlar ‎‎(Mespilus germanica L.) fruit during storage period

Medlar (Mespilus germanica L.) is grown wildly in the East Azerbaijan province (Arasbaran). To evaluate the effect of different concentrations of sodium nitroprusside (SNP)(0, 3, 5 and 8 µM /L) on quantitative and qualitative parameters of medlar fruits during cold storage (1±1°C and 85-95% relative humidity) at five storage times (0, 15, 30, 45 and 60 days), a study was conducted in a factorial experiment based on a completely randomized design with three  replications. According to the results, the highest and lowest percentage of fruit weight loss were obtained at control (2.24 %) and 5 μM/L SNP (1.36 %) during storage, respectively. Fruit color parameters such as L*, hue, chroma and firmness of fruit were maintained at 5 μM/L SNP compared to control. The SNP at 3 µM/L was able to maintain total phenol, total flavonoid, total tannin at high levels and prevent increased polyphenol oxidase (PPO) activity during storage compared to the control. Also, total antioxidant capacity based on DPPH method and activity of antioxidant enzymes such as catalase (CAT) and guaiacol peroxidase (GPX) at 8 µM/L SNP were higher than control. Therefore, SNP seems to increase the postharvest quality of medlar fruit via maintaining the membrane integrity, maintaining phenolic compounds, and reducing the activity of PPO enzyme. In general, it can be concluded that the SNP at 3 µM/L could prevent the excessive reduction of fruit compounds during the storage period.