Alleviating chilling injury in postharvest sweet basil and holy basil leaves by melatonin: insights into oxidative damage and phenolic-related enzymatic activities under low-temperature storage

Abstract

Sweet basil (Ocimum basilicum) and holy basil (Ocimum tenuiflorum) are sensitive to low temperatures and typically exhibit chilling injury (CI) as brown spots on the leaf surface. This study aimed to investigate the effects of melatonin on alleviating CI, oxidative damage, and phenolic-related enzymatic activities in sweet and holy basil leaves. Melatonin was sprayed at concentrations of 0, 50, 100, 200, and 400 µM before storage at 6 °C for 8 days. The results showed that holy basil began to exhibit CI on day 2 and surpassed the acceptable threshold by day 4, whereas sweet basil started showing symptoms on day 4 and exceeded the threshold by day 6. Application of 200 µM melatonin can extend shelf life up to 2 days and reduce CI in both species by 20–22% compared to the control throughout storage. Additionally, melatonin can reduce electrolyte leakage by 9% in sweet basil and 24% in holy basil, decrease malondialdehyde level by 12% and 21%, and lower hydrogen peroxide content by 18% and 31%, respectively. Melatonin also maintained antioxidant capacity by 23% higher than the control in sweet basil and 58% in holy basil, and increased total phenolic content by 13% and 62%, respectively. Furthermore, melatonin also reduced polyphenol oxidase and peroxidase activities in holy basil by 19% and 24%, respectively. Although sweet basil responds physiologically less than holy basil, melatonin can still reduce CI to a similar extent, which indicates different mechanisms of action in each plant species.