Intermittent heat treatment inhibiting heat injury and improving storage quality of cucumber

Abstract: With the increasing concern over the presence of chemical residues in plants, heat treatment, as a safe and effective physical treatment method, has achieved growing interest. To investigate the effects of intermittent heat treatment on cucumber heat injury and storage quality, tested cucumbers were immersed in hot water (38℃) for 60 min (group H) continuously, or 60 min (group I) intermittently, respectively, and the intermittent treatment was realized through the temperature return process by room temperature water (20℃) after every 10 min of continuous treatment. There was no treatment of the control group (CK). All cucumbers were then transferred to cold storage at 12℃ with a relative humidity of 90 percent for 15 days. The distribution of cucumber internal temperature during heat treatment was measured, and the quality and antioxidant enzyme parameters, such as respiratory rate, weight loss, firmness, cell membrane permeability, peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) activities, were evaluated during the cold storage every three days.Results showed that, compared with the control group, the higher respiratory rate, weight loss, cell membrane permeability, and the lower firmness in heat treated cucumbers indicated that the phenomenon of heat injury occurred in group H. There was no significant difference between groups CK and H in antioxidant enzymes (POD, SOD and CAT) (P>0.05). At the end of storage ,the respiratory rate, firmness and relative conductivity of H were 1.19, 92 percent and 1.13 times that of CK. While group I demonstrated delayed cucumber ripening, and performed better in both quality and antioxidant enzymes, at the end of storage, the respiratory intensity, weight loss, POD, SOD and CAT activities were 80 percent, 55 percent, 1.41,1.67, and 1.24 times that of CK. In addition, results from the analysis of the dynamic temperature field of cucumber tissue suggested that the highest temperature that the cucumber tissue achieved and the duration at that temperature were the internal factors for heat injury. The early stage of the heat treatment, with the faster temperature change, was the important stage for preservation effect for cucumbers.