Effect of low oxygen conditioning and ultralow oxygen storage on the volatile profile, ethylene production and respiration rate of ‘Royal Gala’ apples

• We studied the gradually oxygen lowering before apple storage in ultralow oxygen.
• 0.5 kPa O2 maintain higher quality as compared to 0.7 kPa.
• 0.5 kPa O2 reduces straight-chain esters concentration after long-term storage.
• Immediate O2 reduction is not mandatory for high quality maintenance.

The main goal of the present study was to evaluate the conditioning time to ultralow oxygen partial pressures (ULO) on the volatile profile and physical quality of ‘Royal Gala’ apples, after eight months of storage under two ULO levels (0.5 and 0.7 kPa O2). Volatile compounds were analyzed and semi-quantified via GC/MS gas chromatography. Esters originated from fatty acids are strongly affected by oxygen partial pressures. The conditioning to ULO, regardless of period, did not increase the key esters of ‘Royal Gala’ apple aroma, like 2-methyl butyl acetate, butyl acetate and hexyl acetate. Fruits stored under 0.7 kPa O2 presented higher concentration of straight-chain esters, however the storage at 0.5 kPa O2 kept a lower ethylene production and respiration rate, resulting in higher flesh firmness and lower mealiness incidence. Results of this work also proved that immediate oxygen partial pressure reduction, on the first day of the chamber closure, is not mandatory for high quality maintenance after storage, and this fact can optimize the CA installation logistic of storing companies.