Controlled atmosphere (CA) storage is used to maintain the fresh quality of most commercial varieties of apples in the US. CA storage units are typically operated at O2 levels below 3 kPa and CO2 levels between 1 and 5 kPa. However, 'Honeycrisp' fruit is very sensitive to standard CA conditions, which can cause jagged-edged brown lesions in the fruit cortex and lens-shaped voids. The brown lesions develop rapidly, maximizing within the first 1.5 months of CA storage, and the voids develop more slowly, increasing in frequency with storage time. We found that the severity of CA-injury rose with increasing CO2 concentrations. The fruit treated with the antioxidant diphenylamine (DPA) before CA storage experienced minimal CA injury. The damage caused by elevated CO2, in combination with 3 kPa O2, induced the formation of fermentative volatiles ethanol, ethyl acetate, and acetaldehyde. Our data suggested that the fermentative volatiles do not cause damage, but rather they are the result of the damage caused by CA conditions. The injury was found to be associated with changes in cellular metabolites associated with energy interconversion and reducing potential. CA injury was associated with a shortage of reducing agents in ‘Honeycrisp’ apple. The data suggest that the tissue does not have enough adenylate energy charge (AEC) for cellular survival and sufficient antioxidants for scavenging oxygen free radicals that accumulate under CO2 stress. Consequently, cell death follows, leading to the browning symptoms and lens-shaped voids of CA injury.
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