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February / March 2023

Ozone and the treatment of superficial scald

SA Fruit Journal: February / March 2023

The long-term cold storage needed to successfully export fresh fruit, can cause harm to the very produce it's meant to protect. By Dr Asanda Mditshwa

A fresh look at ozone may be good news for apples when it comes to treating superficial scald.

Superficial scald (a.k.a. storage scald) is a major physiological disorder caused by extremely low temperatures. The skin browning seen in superficial scald is caused by the oxidation of -farnesene, a volatile compound that is naturally produced in apples, and that accumulates in the wax layer during the first 8 – 12 weeks of cold storage.

Scald develops more readily when fruit is harvested before physiological maturity, as is typically the case for export produce that spends many weeks in cold storage. "Granny Smith" apples, which are picked while immature to maintain their green colour, are particularly at risk of superficial scalding.

Synthetic chemicals such as diphenylamine (DPA) and 1-MCP have long been used to control superficial scalding. However, as the demand for chemical-free fresh produce grows, so does the need to develop new, non-chemical postharvest treatments.

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