Controlled atmospheres attenuate husk scald in pomegranates by reducing oxidative stress, modulating hormones, and delaying senescence

Husk scald (HS) is a significant postharvest disorder in pomegranates (Punica granatum L., cv. Wonderful), characterized by external browning that adversely impacts marketability without affecting internal quality. Controlled Atmosphere (CA) storage has been reported to attenuate HS, however the mode action needs to be elucidated. This study explores the impact of CA storage, specifically low oxygen (3% O2, LO) and low oxygen with high carbon dioxide (3%O2 + 10% CO2, LO + HCO₂), in mitigating HS during storage at 11°C and 95% relative humidity for up to 85 days. Physiological, biochemical, and molecular analyses were conducted to elucidate the mechanisms underpinning HS development and its suppression under CA conditions. Results demonstrate that CA storage did not affect weight loss, but significantly reduced browning index, and HS incidence compared to ambient air (AIR). LO + HCO₂ conditions preserved phenolic content and antioxidant activity, as evidenced by higher levels of total phenolics (TP) and anthocyanins (TA) and reduced lipid peroxidation markers such as malondialdehyde (MDA). Enzymatic activity linked to oxidative stress, polyphenol oxidase (PPO) and phenylalanine ammonia-lyase (PAL), was markedly suppressed under CA storage, correlating with reduced browning and oxidative damage. Hormonal analysis revealed that JA and ABA levels, key regulators of stress responses, were significantly lower in CA-treated fruits, highlighting the role of CA storage in attenuating stress-related metabolic pathways. Temporal analysis revealed a sequential cascade: water loss triggered JA accumulation (days 0–20), which activated NOX-mediated ROS generation, subsequently inducing ABA biosynthesis (days 20–50), culminating in self-amplifying feedback loops involving JA, ABA, and ROS (days 50–85). The expression of antioxidant defense genes (CAT, SOD) and browning-related genes (PAL, PPO) was also downregulated under CA conditions, providing mechanistic insights into the mitigation of HS. CA storage disrupts this cascade through oxygen limitation: low O₂ inhibits JA biosynthesis and NOX activity, preventing ROS accumulation and thereby blocking ABA induction and feedback amplification. These findings suggest that CA storage modulates oxidative stress, enzymatic browning, and hormonal responses, delaying the onset of senescence and preserving fruit quality. This study represents a novel approach in pomegranate postharvest management by integrating physiological, biochemical, and molecular analyses to address HS. The findings highlight the efficacy of CA storage in extending storage life and marketability, offering a sustainable solution for reducing postharvest losses and enhancing economic returns for pomegranate producers.