Possible Mechanisms by Which Postharvest Calcium Treatment Reduces Decay in Apples

Abstract

''Golden Delicious'' applies were pressure-infiltrated (68.95 kPa [kilopascal]) with 0, 2, 4, 6 or 8% solutions of CaCl2 and stored at 0.degree. C. Another lot of fruits was stored in low (1%) O2 storage (0.degree. C). After 6 mo. of storage, both lots were wound-inoculated with Penicillium expansum and incubated for 7 days at 20.degree. C. The fruits treated with 4.6 or 8% CaCl2 and the fruits kept in low O2 were equally firm. Whereas the area of decay was reduced by only about 15% in fruits kept in low O2, fruits infiltrated with 4, 6 or 8% CaCl2 solutions had more than 50% less decay than nontreated fruits. Fungal growth on media was not retarded when dehydrated PDA and PDB were amended with CaCl2 to a concentration of Ca at least twice that encountered by the fungus in the fruit. There was no correlation between total phenolic compounds in the flesh and Ca concentration of the tissue. The effect of Ca in reducing decay is indirect and may be due to the formation of cell wall components resistant to degradation by P. expansum.