Pseudomonas graminis strain CPA-7 differentially modulates the oxidative response in fresh-cut 'Golden delicious' apple depending on the storage conditions

The oxidative response in fresh-cut antioxidant-treated 'Golden delicious' apples during chilling storage was differentially modified by the biopreservative bacterium Pseudomonas graminis CPA-7 depending on the storage conditions (passive modified atmosphere packaging (MAP) or air). Results showed that inoculation with CPA-7 had no influence on fruit quality parameters in any of the conditions tested. During the first 24 h both in air and in MAP, ascorbate peroxidase (APX) activity triplicated the initial level in response to CPA-7, reaching up to 4-fold the activity of non-inoculated fruit (control). From 24 h of storage in MAP, polyphenol oxidase (PPO) activity was sharply enhanced in response to CPA-7 attaining values up to 8-fold higher than that of the control at the end of the experiment, yet it was not paired to an increase in browning incidence. Concomitantly, at 24 h of storage in MAP, CPA-7 suppressed peroxidase (POX) and catalase (CAT) activities. Subsequently, after 3 d in such conditions, superoxide dismutase (SOD) and PPO activities were almost duplicated in the presence of CPA-7 compared to the control. On the other hand, when stored in air, POX showed a biphasic induction in response to CPA-7 after 1 d and 6 d of incubation. On day 6, this enzyme duplicated its activity in inoculated samples compared to the control regardless of storage conditions. Inoculation with CPA-7 led to the slowdown of the decline of antioxidant capacity in air, which contrasted with the response upon MAP conditions. These results suggest that CPA-7 may trigger the activation of the fruit defense-response thereby mitigating its oxidative damage. Such activation may play a role as a putative biocontrol mechanism against foodborne pathogen infections.