Nitric oxide delays chlorophyll degradation and enhances antioxidant activity in banana fruits after cold storage

The effect of nitric oxide (NO) on chlorophyll degradation and antioxidant response in banana fruits after cold storage was investigated. Pre-climacteric green banana fruit treated with NO donor sodium nitroprusside of 0.05 mM was stored at 7 °C for 15 days and then ripened at 22 °C for 6 days. Chilling injury (CI) index, color, chlorophyll, total phenolics, activities of chlorophyllase, Mg-dechelatase, catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (POD), phenylalanine ammonia-lyase (PAL) and polyphenol oxidase (PPO) of the banana peel, together with firmness, titratable acidity (TA) and total soluble sugar (TSS) of the banana pulp were analyzed in this research. NO treatment improved chilling tolerance of banana fruits as shown by the reduced CI index. The retarded color change of the peel and higher firmness, TA and TSS content of the pulp showed that ripening process of NO-treated banana fruit was delayed by 2 days. The activities of chlorophyllase and Mg-dechelatase were significantly inhibited by NO, resulting in the retention of chlorophyll content. Further investigation showed that activities of CAT, APX and POD were enhanced in NO-treated banana fruits. Compared to control fruits, NO treatment significantly promoted PAL activity and inhibited PPO activity, and thus led to higher levels of total phenolics content. Results suggested that NO could enhance both enzymatic and non-enzymatic antioxidant system, and thus retarded chlorophyll degradation of banana fruits. Due to its effect on inhibition of chlorophyll degradation enzyme activities and promotion of the antioxidant defense system, NO is suggested as a potential approach to preserve chlorophyll content and maintain fruit quality of banana fruits after cold storage.