Nitric oxide fumigation alleviates chilling injury and regulates fruit quality in sweet orange stored at different cold temperatures

Abstract

The cold storage of sweet oranges below 7 °C causes chilling injury and adversely affects fruit quality. Midknight Valencia and Lane Late sweet oranges were fumigated for 2 hours with different concentrations (5, 10 or 20 µL L-1) of nitric oxide (NO) and stored at (4 or 7 °C) to investigate the effect on chilling injury incidence (CI) and fruit quality after 90 days storage followed by 10 days simulated shelf conditions. Untreated fruit served as a control. The experimental design completely randomised with two factors including NO fumigation treatments and storage temperatures. All NO fumigation treatments (5, 10 or 20 µL L-1) significantly reduced the CI irrespective of storage temperature as compared to the control in both the cultivars. Fruit were fumigated with different concentration of NO gas in a sealed container for 2 h and then kept at 4°C and 7°C. Fruit quality variables such as fruit firmness, SSC (%), TA (%), SSC/TA, sugars, vitamin C and total antioxidants were determined. All the NO treatments significantly reduced per cent weight loss as compared to control in Lane Late. Mean weight losses were higher (8.3 % and 5.5 %) when fruit were stored at 7 °C as compared to those stored at 4 °C (4.8 % and 3.5 %) in Midknight Valencia and Lane Late respectively. All the NO fumigation treatments significantly reduced the mean concentrations of glucose, fructose, sucrose and total sugars in the juice of Midknight Valencia only. All NO fumigation treatments significantly reduced mean concentration vitamin C in the fruit juice of Lane Late as compared to the control. Meanwhile, in Midknight Valencia, NO (10 or 20 µL L-1) fumigated fruit showed a significant reduction in the mean concentration of vitamin C as compared to NO (5 µL L-1) fumigation and control. The juice of Midknight Valencia had higher mean total antioxidants when fumigated with NO (5 µL L-1) as compared to the control, but not in Lane Late. In conclusion, all the NO fumigation (10 µL L-1) treatment was most effective in reducing CIin both cultivars irrespective of the cold storage temperature. NO fumigation treatments did not affect SCC/TA ratio but reduced all the individual and total sugars as well as vitamin C in the fruit stored for 90 days followed by 10 days simulated shelf conditions.