Submitted to: Postharvest Biology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 21, 1999
Publication Date: N/A
Interpretive Summary: Superficial scald is a serious, costly storage disorder of apple and pear fruits. The main symptom of scald is marked discoloration of the skin which makes the fruit unacceptable for fresh market sales. Scald can be largely controlled by treating fruit with the antioxidant DPA, but this drench treatment requires use of a fungicide as well, resulting in chemical lresidues on the skin that could pose a health risk. This study examined the biochemical basis of the prevention of scald in apples by DPA treatment and low oxygen atmosphere storage. It also resulted in a relatively simple method for determining the level of DPA residue in apple peel tissue. The objective of this work is to find safer and less expensive means of controlling scald. This will benefit the apple industry by eliminating the cost of postharvest chemical treatments and opening foreign markets that forbid the sale of treated fruit. The consumer and general public will also benefit as a consequence of fewer chemical residues on the apples and reduced release of potentially hazardous chemical waste into the environment.
Treatment with diphenylamine (DPA) and storage under low oxygen are the major commercial means of limiting superficial scald in apple fruit. Synthesis and oxidation of 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 in vitro and in vivo oxidation of ffarnesene to conjugated trienes (CTs), but DPA reportedly has multiple effects, including reduction of farnesene synthesis, ethylene production, and respiration. The time course and levels of 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 0C in air or under 1.5 percent oxygen. Also, it was found that the HPLC-UV method developed to quantify farnesene and CTs could be used to simultaneously measure the concentration of DPA residue. In air-stored fruit, DPA treatment protracted rather than diminished farnesene synthesis; a similar maximum level of farnesene was reached at 15 and 28 weeks in untreated and DPA-treated fruit, respectively. DPA treatment delayed the onset of CT production by about 5 weeks and reduced CT accumulation more than 2.5-fold. Low oxygen was overall more effective than DPA treatment in reducing synthesis and oxidation of farnesene. In combination, DPA and low oxygen had a synergistic effect, resulting in a 9-fold reduction in farnesene and virtual elimination of CT production over 28 weeks. In both air and 1.5 percent oxygen, DPA residue in peel tissue declined rapidly during the first 15 weeks of storage and more gradually thereafter, with an overall drop from about 11 to 1.1 ug per g.