DPA treatment alters alpha-farnesene metabolism in peel of 'Empire' apples stored in air or 1.5% O-2 atmosphere

Treatment with diphenylamine (DPA), sometimes in combination with storage under low(less than or equal to 1.5%) O-2 atmosphere, is the major commercial means of limiting superficial scald in apple fruit. Synthesis and oxidation of the sesquiterpene alpha-farnesene are thought to be directly involved in induction of this storage disorder. Control of scald by DPA has been ascribed to its ability to block both in vitro and in vivo oxidation of alpha-farnesene to conjugated trienes (CTs), but a number of reports have indicated that DPA has multiple effects, including reduction of alpha-farnesene synthesis, ethylene production, and respiration. The time course and levels of alpha-farnesene and CT accumulation in peel tissue were compared in 'Empire' apples that were either DPA-treated or untreated and stored for up to 28 weeks at 0 degrees C in air or under 1.5% O-2 atmosphere. Also, it was found that the HPLC-UV method previously developed to quantify alpha-farnesene and CTs could be used to simultaneously measure the concentration of DPA residue. In air-stored fruit, DPA treatment protracted rather than diminished alpha-farnesene synthesis; a similar maximum level of alpha-farnesene was reached at 15 and 28 weeks in untreated and DPA-treated fruit, respectively. DPA treatment delayed the onset of CT production by similar to 5 weeks and reduced CT accumulation more than 2.5-fold. The low O-2 atmosphere was overall more effective than DPA treatment in reducing synthesis and oxidation of alpha-farnesene. In combination, however, DPA and low O-2 had a synergistic effect, resulting in a ninefold reduction in alpha-farnesene and virtual elimination of CT production over 28 weeks. In both air and 1.5% O-2, DPA residue in the peel tissue declined rapidly during the first 15 weeks of storage and more gradually thereafter, with an overall drop from similar to 11 to 1.1 mu g g(-1). (C) 2000 Elsevier Science B.V. All rights reserved.