Heat Treatment Affects Postharvest Quality of Kale and Collard, but not of Brussel Sprouts
Mature leaves of kale (Brassica oleracea L., Alboglabra group) and collard (Brassica oleracea L., Acephala group), and Brussels sprouts (Brassica oleracea L., Gemmnifera group) were heated by moist air at 40, 45, 50, or 55 ºC for durations of 0, 30, 60, or 90 minutes. Heating of kale at 45 ºC for 30 minutes was effective in maintaining better postharvest quality, delaying yellowing, and reducing losses of sugars and organic acids during subsequent storage at 15 ºC. Exposure of collard at 40 ºC for 60 minutes also delayed yellowing and maintained turgidity of the leaves. Other treatments were either less beneficial, not effective, or caused injury. Heat injury occurred when temperature and duration exceeded the tolerance levels. In some cases, heat-injured tissues remained green but developed fungal infection. Heat treatments had no measurable effects on the rate of senescence or storage quality of Brussels sprouts.