Effect of heat or 1-methylcyclopropene on antioxidative enzyme activities and antioxidants in apples in relation to superficial scald development

Granny Smithʼ apples (Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.) were harvested in two seasons and stored at 0 oC air storage with no pretreatment (control), after heating for 4 d at 38 oC, or after treating for 16 hours at 20 oC with 1 µL·L-1 1-methylcyclopropene (1-MCP). The effects of the two treatments on superfi cial scald development were consistent over both seasons. Scald began to appear after 8 weeks in control fruit, after 16 weeks in heated fruit but not on 1-MCP treated fruit. α-Farnesene accumulation and oxidation were slower in the skin of heated than in control fruit, and almost entirely absent in 1-MCP treated fruit. The activities of fi ve antioxidant enzymes, ascorbate peroxidase, catalase, glutathione reductase, peroxidase and superoxide dismutate, were measured at two-week intervals in the apple peel, quantitatively as total activity and qualitatively by isozyme analysis. Enzyme activities either increased or remained stable during 16 weeks of storage, except for superoxide dismutase activity, which decreased. Ascorbate oxidase activity was higher in heated than control apples and there was an additional peroxidase isozyme present in activity gels. The activities of antioxidant enzymes were lower in 1-MCP treated fruit except for catalase during the fi rst month of storage. Lipid soluble antioxidant activity was higher in 1-MCP treated fruit than the fruit of the other treatments, and water soluble antioxidant activity was higher in both treatments than in control fruit during the time that scald was developing in control apples. Both free and total phenol contents in the peel fl uctuated during storage but no consistent trend was detected. The differences in enzyme activity and antioxidant content of the peel of 1-MCP and heated apples may play a role in preventing or delaying the appearance of superfi cial scald. It is widely accepted that synthesis and oxidation of the ses- quiterpene α-farnesene play a central role in development of superfi cial scald, a physiological storage disorder of apples and pears (Anet, 1972a, 1972b; Huelin and Coggiola, 1968; Huelin and Murray, 1966; Ingle and DʼSouza, 1989). Accumulation of high levels of conjugated trienols, the oxidation products of α- farnesene, in the fruit epidermis is closely correlated with the subsequent appearance of scald symptoms, whereas high levels of α-farnesene itself are less well correlated with scald (Anet, 1972b; Huelin and Coggiola, 1968, 1970a). This may be in part attributed