Postharvest intermittent heat treatment alleviates chilling injury in cold-stored sweet potato roots through the antioxidant metabolism regulation

The effects of intermittent heat treatment (HT) on chilling injury (CI) and antioxidant capacity of sweet potato roots were investigated during cold storage at 5 +/- 0.5oC and 80%-85% relative humidity. Roots were heat treated in an air oven (45oC) for 3 hr continuously (HT45) or intermittently (I-HT45). Intermittent treatment was achieved through the temperature recovery by room temperature after every 1 hr of continuous treatment. Results indicate that both continuous and intermittent HTs maintained the root quality and improved cold damage resistance to varying degrees compared with the control group. I-HT45 had the lowest CI index, electrolyte leakage and malondialdehyde content while maintaining the roots' well-organized microstructure. It also effectively blocked superoxide radical and hydrogen peroxide accumulation by activating catalase and superoxide dismutase activities. The present study provided a safe physical method to mitigate CI of cold-stored sweet potato roots by regulating antioxidant metabolism to alleviate the oxidative damage. Practical applications Sweet potato is the world's seventh most important food crop, and more than 70% is produced in China. However, due to its tropical origin and lack of temperature-controlled storage, roots are prone to CI during on-farm storage, long distance transport, or when it reaches the markets. Heat treatment (HT) occupies a predominant position in postharvest conditions for alleviating physiological disorders and reducing CI. However, continuous HT may cause thermal damage such as flesh browning, microstructure failure, and low antioxidant capacity. Intermittent HT will not only prevent heat damage by interrupting the accumulation of thermal stress but also achieve better preservation by promoting the generation of heat shock effect. The aim of this study is to evaluate the application of intermittent HT on cold resistance, antioxidant level, and microstructural changes, then provide a potential strategy for maintaining quality and prolonging the storage period of sweet potato roots subjected to cold storage.