Effect of short-term gaseous ozone treatment on postharvest quality and shelf-life of ‘Eureka’ lemons.

Abstract

Citrus is globally one of the commonly consumed fruits, its consumption has steadily increased over the last decades. It has a significant contribution to the South African economy and employment. The 2024 report by Citrus Growers’ Association (CGA), indicated that South Africa exported 164.5 million 15kg cartons of citrus, with lemons contributing 21% of exports. Similar to other fresh produce, ‘Eureka’ lemons are highly sensitive during postharvest handling and their quality tends to deteriorate. The postharvest treatments are necessary to minimize the quality loss and extend the shelf-life. Gaseous ozone (O3) is an emerging postharvest treatment for preserving the postharvest quality and extending the shelf-life of fresh horticultural produce. Therefore, this study explored the effect of the short-term gaseous ozone on the quality of ‘Eureka’ lemons. The study aimed to: 1) investigate the effect of gaseous ozone on the physical attributes on the quality and shelflife (Chapter 3); 2) assess the effect of gaseous ozone in antioxidant and biochemical attributes (Chapter 4); and lastly, evaluate the impact of gaseous ozone on senescence-related enzymes of ‘Eureka’ lemons during cold storage (Chapter 5). The first experiment investigated the effect of gaseous ozone on the physical quality attributes such as decay, mass loss, colour and firmness. The findings revealed O3(48h) caused severe decay, this treatment showed high decay incidence as compared to the O3(24h) and the untreated lemons. However, for mass loss, firmness and colour, the O3(48h) treatment showed positive results as there was a relatively lower loss compared to the other treatments. The second experiment revealed that ozone treatment duration has a significant impact on the biochemical attributes of the fruit. For instance, O3(24h) treatment positively affected the phenolics, flavonoids and DPPH. However, O3(48h) showed a positive influence on the carotenoids, ascorbic acid and condensed tannins. This shows that biochemical parameters exhibit unique responses to the oxidizing power of ozone. The third objective assessed the impact of gaseous ozone on senescence-related enzymes such as catalase, peroxidase, lipoxygenase and glutathione reductase as well as lipid peroxidation. This experiment revealed that O3(24h) is effective in preserving the senescence-related enzymes as there was an increase from Day 0 to Day 35 in all the enzymes. On the other hand, the O3(48h) treatment at ambient storage showed a decreasing trend in catalase, lipoxygenase and glutathione reductase. Ozonation inhibits the accumulation of O2 and H2O2 which is associated with the higher activity of the peroxidase. Based on these findings, O3(48h) is less likely to be recommended as it carries high oxidizing power which adversely affects the quality of the fruit. The O3(24h) revealed the possibility of maintaining the quality without severely affecting the fruit. There is however a need to further optimize the ozone treatment protocols, for instance, the performance of O3(36h), which is slightly lower than the 48h, should be assessed. Also, the combination of gaseous ozone and the edible coatings should be explored.