The effect of ozonated cold storage on superficial scald incidence of ‘Granny Smith’ apples

Superficial scald is one of the prominent physiological disorders affecting the quality of apples. Among apple cultivars, ‘Granny Smith’ has high susceptibility to superficial scald incidence. While various methods have been developed to control scalding, there is a constant need to develop effective, innovative, environmental-friendly and cost-effective strategies for inhibiting this disorder. The use of ozone as a postharvest treatment has gained global popularity in recent years. This is largely due to its antioxidant properties and ability to reduce ethylene accumulation thereby prolonging the shelf-life of various horticultural products. Thus, the aim and objective of this study was to investigate the effect of gaseous ozone on superficial scald incidence of ‘Granny Smith’ apples

‘Granny Smith’ apples harvested at pre-optimal maturity were placed in three cold storage chambers controlled at 0 °C and 95% relative humidity. Two ozone regimes were used in order to determine the most suitable exposure time for preventing scalding. The fruit was exposed to continuous 0.3 ppm ozone treatment for either 24 hours or 48 hours. Untreated fruit was used as a control treatment. The fruit was stored for a duration of 21 weeks and the quality assessments were conducted at three-week intervals. Fruit quality assessment was conducted after 7 days of shelf-life. The assessed parameters included scald incidence (%), total soluble solids, titratable acidity, antioxidant capacity, ascorbic acid, α-farnesene and conjugated trienols.

The findings showed that ozonated atmospheres have the potential to retard superficial scald incidence of apples. After 21 weeks of storage, the control treatment had 70% scald incidence compared to 45% and 65% for fruit stored in 0.3 ppm ozone for 24 hrs and 48 hrs, respectively. Fruit stored for 24 hrs in ozone had superior appearance compared to those stored in control or 48 hrs ozone treatment. Throughout the storage, the 24-hr ozone treatment had high colour retention and low ethylene production. Moreover, the concentration of ascorbic acid and conjugated trienols was significantly lower in fruit exposed to gaseous ozone before long-term storage.

Gaseous ozone demonstrated the potential of reducing superficial scald of ‘Granny Smith’ apples. However, the significant incidence of scalding (45%) in fruit stored in ozonated atmosphere is a cause of concern. Overall, ozonated fruit had superior quality including high colour retention and antioxidant activity. Moreover, ethylene production as well as conjugated trienols were significantly lower in ozonated fruit.

Gaseous ozone has various benefits for the apple fruit industry. Its effect on postharvest diseases has been considerable studied. Thus, its inhibitory effect on superficial scald is an added benefit that could significantly reduce the cost of postharvest treatments. As above mentioned, the slight scalding in ozonated fruit is a concern, thus, the possibility of combing gaseous ozone with other postharvest treatments or technologies such as 1-MCP or controlled atmosphere (CA) should be considered.