Effects of postharvest chilling and heating treatments on the sensory quality and antioxidant system of daylily flowers

Abstract

Temperature is the most important factor that affects the metabolism of harvested plants. The aim of this study was to investigate the influence and mechanisms of temperature on the antioxidant system in fresh-cut daylily flowers (Hemerocallis lilioasphodelus L.; used for food consumption) during storage. Daylily flowers were harvested and immediately treated by either chilling at 5 °C for 5 days, or by heating with 50 °C hot air for 5 min, then stored at 20 °C for 5 days. The chilling and heating treatments maintained the organoleptic quality and enhanced the antioxidant system of cut daylily flowers. However, different reactions of the antioxidant system were observed under the different temperature treatments. The chilling treatment dramatically enhanced the activities of superoxide dismutase, ascorbate peroxidase, peroxidase, and phenylalanine ammonia lyase, while it decreased the activity of lipoxygenase. Meanwhile, the heating treatment enhanced catalase activity and decreased polyphenol oxidase activity. In addition, the heating treatment reduced the O2− production rate and H2O2 content compared to the control. Changes in membrane permeability, total phenolic content, total flavonoid content, and diphenyl-1-picrylhydrazyl clearance activity showed no significant difference between the chilling and heating treatments, owning to the steady content of phenolic and flavonoid compounds and the delay in the generation of quinones. Thus, our results indicate that cold and heat treatments can impact the preservation of harvested daylilies used for food consumption.