Effect of heat treatment on postharvest quality of kale, collard and brussels sprouts

The effect of heat treatment with moist air at temperatures of 40, 45, 50, or 55 degrees C for durations of 0, 30, 60, or 90 minutes was studied in mature leaves of kale (Brassica oleracea L., Alboglabra group) and collard (Brassica oleracea L., Acephala group), and Brussels sprouts (Brassica oleracea L., Gemmifera group). The optimal heat treatment for kale was found to be at 45 degrees C for 30 minutes and resulted in higher postharvest quality, delayed yellowing, and less decline of sugars and organic acids with later storage at 15 degrees C. Collard treated with 40 degrees C for 60 minutes had the best maintenance of leaf structure and latest onset of yellowing, compared to the other heat treatments. When temperature and duration exceeded tolerance levels, heat injury was observed. In some cases of heat injury, tissues maintained their green color but developed fungal infection. In Brussels sprouts, heat treatments caused no significant effects in the rate of senescence or storage quality.