Revealing the mechanism underlying the use of preharvest nano-emulsion of citrus essential oil for reducing browning injury and maintaining postharvest quality of chili during cold storage

The transportation and storage of chili in cold storage are beneficial for handling from farm to household; however, browning injury and quality loss during cold storage are the main concerns. This study explored a new method for preharvest chili plants to reduce browning injury and maintain postharvest quality during cold storage (4 ± 2 °C) for at least 40 days. Citrus essential oil (lime oil and orange oil) nanoemulsion at a low concentration of 0.006 % v v⁻¹ was applied to chili plants for 10 days before the 1st harvest at 90 days and the 2nd harvest at 120 days. Both the first and second harvest chili fruits were kept under cold storage for 40 days. Color change, pigment, bioactive compounds, and quality of chili were measured. Results showed that citrus nanoemulsion could be absorbed from the roots of chili plants and pass through the flowers and fruits. The treated chilies were firmer, more water-resistant, and had a longer fruit length than the control. Treated chili also displayed delayed color change, ripening from green to red, increased brightness, and reduced browning injury on both the surface and seeds. Furthermore, higher total phenolic content, total flavonoid content, and antioxidant activity were confirmed in the treated chili, which helped to maintain the quality of the chili fruit from 20 days (control) to 40 days, with a slight disease incidence (17 %) and low weight loss (7 %) compared to the control (54 % disease incidence and 64 % weight loss). Orange oil nanoemulsion showed greater quality preservation than lime oil due to the higher limonene content found on the chili surface, around 5.7 % for chili treated with orange oil compared to 0.7 % for lime oil. This finding indicates a method to reduce browning injury and prolong the shelf life of chili during cold storage. It is easy to implement in chili farming, allowing for at least two harvests before the next pretreatment, benefiting both farmers and consumers.