During storage of apples at 1° the concentration of a‐farnesene in the ‘coating’ (mainly cuticle) and adjacent cells increased to a maximum and then declined. At the highest maximum farnesene was 15% of the total lipid of the coating. Evidence is presented for a role of a‐farnesene in superficial scald. More a‐farnesene was found in earlier picked apples and more in the scald‐liable Granny Smith than in the scald‐resistant Crofton variety. During storage a‐farnesene moved from the fruit to the oiled wraps until wraps contained more than twice as much as the fruit. Diphenylamine reduced the production of a‐farnesene in later picked apples.

a-Farnesene was oxidised to conjugated trienes with an absorbance maximum at 269 nm and the oxidation was inhibited by diphenylamine both in hexane solution and in the natural coating of stored apples. The results suggest that superficial scald is caused by the oxidation of a-famesene and that the control of scald by diphenylamine is due to its antioxidant action. The mechanism of scald induction is discussed.

The a-farnesene content of apples usually passed through a maximum during storage. Studies in the range 0 to 15"c indicated that the highest maximum was reached at approximately 5"c. The concentration of total lipid and fatty acids in the coating increased with temperature. Application of a-famesene to the surface before storage inhibited further production of a-farnesene and reduced the production of total lipid and fatty acids.Application of a-farnesene by dipping in ethanolic solution caused injury to the outer cortex which differed from typical scald. Application within marked circles induced typical scald only with previously oxidised famesene. In comparing experiments over five years, conjugated trienes gave a higher correlation with scald than a-famesene or the peroxide value.Superficial scald is discussed in relation to the concentration of a-famesene and its oxidation products and the concentration of natural antioxidants. Tests for artificial antioxidants are discussed. IntroductionMuch evidence for a r61e of a-farnesene in superficial scald was given in previous p a p e r~. l -~ This evidence includes the transfer of a-farnesene to the oiled wrap, the relation of scald to the oxidation of a-farnesene, and the effect of air movement on its evaporation. The oxidation of a-farnesene was studied by Anet,4 who identified two conjugated triene hydroperoxides with U.V. absorbance peaks similar t o those reported for extracts of the natural coating of long-stored apples2Measurements of changes in the concentration of afarnesene during storage of apples at 5 and 15"c in 1967 were included in the experiments on evaporation already reported.3 Comparable samples from the same source in 1967 were stored at 0"c in cartons and analysed at intervals. Comparison of results obtained at the 3 temperatures indicated that the highest concentration of a-farnesene was reached at 5"c, and this result was of sufficient interest to suggest repetition of the effect of temperature in 1968. Attempts to induce superficial scald by applying a-farnesene to the surface of the fruit were initiated in 1968, and peroxide values as a measure

A wide range of antioxidants (amine, phenolic and one sulphur-containing) were all found to inhibit the autoxidation of u-farnesene in vitro. Some were somewhat more effective than others but no class showed any marked superiority.When added to apples as a dip or by injection, only amine type antioxidants inhibited the autoxidation of u-farnesene in vivo. Phenolic antioxidants were ineffective and some acted as pro-oxidants, notably u-tocopherol. In all instances the severity of superficial scald was proportional to the extent of a-farnesene oxidation.