Submitted to: Phytochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 28, 1996
Publication Date: N/A
Interpretive Summary: Consumer concerns over the use of synthetic chemicals to preserve postharvest quality of fresh fruits, and the likelihood that use of these compounds will be banned or restricted in the near future, have prompted testing of various physical and nontoxic chemical treatments to extend shelf life and maintain quality. Both hot air heating and pressure infiltration with solutions of calcium chloride appear promising as means of alleviating physiological disorders and reducing fungal decay during postharvest storage of apple fruit. The mechanisms underlying the beneficial effects of these treatments are not known. This study was conducted to determine if either heat or calcium induce changes in the metabolism of lipids, the structural components of cell membranes, and thereby reduce the rates of ripening, softening, and decay. Results of the work indicated that heating dramatically alters lipid metabolism, whereas calcium infiltration has little effect. This finding supports the proposa that the benefits conferred by the two treatments result from different mechanisms and suggests that changes in cell membranes are an important aspect of the benefits of heating. This information will be useful to other scientists in their efforts to optimize postharvest quality through application of consumer-safe technologies.
Technical Abstract: Heating Golden Delicious apples for 4 days at 38C and/or pressure infiltrating the fruit with a calcium chloride solution after harvest maintains firmness and reduces decay during storage. The possibility that these beneficial effects involve changes in membrane lipid metabolism was investigated. Lipids of hypodermal cortical tissue were analyzed after 0, 1, 2 or 4 days at 38C, and after storage (15 weeks at 0C plus 1 week at 20C) of fruit that were untreated (Ctl), heated 4 days at 38C (HT), infiltrated with 2 percent calcium chloride (Ca), or heated then Ca-infiltrated (HT + Ca) before storage. Overall, effects of HT on lipid metabolism were much more pronounced than those of Ca, and effects of HT + Ca were intermediate to those of HT or Ca alone. An initial phase of membrane damage induced by heating, indicated by phospholipid (PL) and galactolipid loss over the first 1-2 days at 38C, could explain why HT for less than 3-4 days adversely affects quality. HT effects on plastid lipid and pigments are likely to cause the marked yellowing of the fruit. HT induced reductions in steryl glycosides and cerebrosides prior to storage similar to those that occurred in Ctl and Ca fruit during storage, and the PL content of HT fruit after storage was close to that of Ctl fruit at harvest. Also, the 18:2/18:1 ratio in PL was higher in HT and HT + Ca than in Ctl fruit at the end of storage. These effects of HT on lipid composition may help preserve membrane function and thus benefit fruit quality.