Antioxidant Treatment Alters Metabolism and Internal Browning in 'braeburn' Apples During CA Storage

‘Braeburn’ apple (Malus ×domestica Borkh.) fruit can develop internal browning and pitting during storage in elevated levels of CO₂. The antioxidant diphenylamine (DPA) can prevent this disorder.  To evaluate associated metabolism, we employed untargeted metabolic profiling of non-polar, polar, and volatile compounds using GC-MS and LC-MS methods with untreated or 2 g•L^-1 DPA treated ‘Braeburn’ apple fruit stored under high CO₂ conditions at 1.5 kPa O₂/3 kPa CO₂ at 0.5 °C for up to 12 weeks. Partial least squares discriminant analysis (PLS-DA) was employed to identify metabolomic differences that developed during storage and internal browning of untreated and DPA-treated fruit. The PLS-DA scoring plot revealed metabolomic divergence between untreated and DPA treated fruit after 4 weeks of storage, which accompanied increased flesh browning only in untreated fruit. The PLS-DA loading plot indicated that flesh browning was associated with increased acetaldehyde, ethanol, and ethyl esters. DPA treatment reduced the levels of these and other volatile compounds.  DPA treatment also reduced flesh content of many amino acids. These results indicated that metabolism is altered by DPA treatment after 4 weeks of CA storage and these metabolic changes may be related to tissue integrity.