Evaluation of carbon dioxide elevation on phenolic compounds and antioxidant activity of red onion (Allium cepa L.) during postharvest storage.

Carbon dioxide (CO2) is considered one of the eco-related key factors that negatively affect global climatic change. Also, CO2 can play an important role in the postharvest quality of the agri-products. In this study, the impact of CO2 on the quality of postharvest onions that were stored at 23 °C for 8 weeks was investigated. The weight loss, phenolic, flavonoid, flavanol, anthocyanin, antioxidant activity, and soluble sugar were analyzed during the study period. The results showed that 20% CO2 treatment was significantly (P > 0.05) more effective than 15% CO2 and control in inhibiting weight loss. Additionally, 20% CO2 treatment significantly retained higher antioxidant enzyme activities such as CAT, APX, and SOD than 15% CO2 and control. During storage, 20% CO2 treatment significantly (P < 0.05) improved glucose, fructose, and sucrose levels by more than 15% CO2 exposure and control groups. Besides the chlorogenic acid, kaempferol and quercetin were significantly (P < 0.05) higher in the 20% CO2 than in the 15% CO2 after 2 weeks of storage. In conclusion, this study's novelty comes from the broad prospects of using CO2 for maximizing the stored onion phytochemical functionality that is usually affected by the room temperature long storage. This will help in the onion shelf-life extension by considering the quality-related attributes.