Short anaerobiosis period prior to cold storage alleviates bitter pit and superficial scald in Granny Smith apples

BACKGROUND: Californian Granny Smith apples are very susceptible to bitter pit (BP) and superficial scald symptoms that develop during cold storage. The main preventive means are diphenylamine dipping and/or gaseous application of the ethylene inhibitor 1‐methylcylclopropene (1‐MCP), which is effective against superficial scald but not against BP. This study investigated the efficacy of a non‐chemical alternative, low‐O₂ (LO2) stress, in preventing these two physiological disorders. RESULTS: Application of LO2 stress at 20 °C for 10 days prior to cold storage of Granny Smith apples reduced superficial scald and BP incidence and severity during 8 months at 0 °C. LO2 treatments induced volatile alcohols and reduced ethylene and 6‐methyl‐5‐hepten‐2‐one (MHO‐on) production, thereby reducing superficial scald development after 4 months at 0 °C. In addition, LO2‐treated fruits had higher pectin methyl esterase (MdPME) gene expression, similar to that of 1‐MCP‐treated fruits, associated with their higher firmness. Conversion of MHO‐on to 6‐methyl‐5‐hepten‐2‐ol (MHO‐ol) in LO2‐treated fruits may explain the lower scald development. CONCLUSION: The ratio between MHO‐on and MHO‐ol might serve as an index of superficial scald severity. Reduction of BP symptoms in LO2‐treated fruits could be due to accumulation of volatile alcohols in the peel tissue. Copyright © 2010 Society of Chemical Industry