CHANGES IN COLOR AND CHLOROPHYLL FLUORESCENCE OF BROCCOLI FLORETS FOLLOWING HOT-WATER TREATMENT

Hot water treatments (HWTs), at a range of temperatures (43 to 55C) an d durations (10 sec to 30 min), were applied to floret groups of 'Shog un' broccoli (Brassica oleracea L. var italica) directly after harvest , Floret groups were then stored at 20C in the dark for 3 days. A rang e of optimal treatments was found in which yellowing was markedly redu ced, acid heat damage (water soaking and decay) did not occur. Chlorop hyll fluorescence measurements indicated that in the optimum treatment that prevented yellowing the FvFm ratio following HWT decreased immed iately and was maintained at a constant level for the next 3 days. A f urther experiment examined the effect of HWT durations up to 20 min at 47C on fluorescence and yellowing, Longer durations of HWTs (>5 min) progressively reduced yellowing and the F-v/F-m ratio. From these thre e experiments a HWT of 47C for 7.5 min was selected as the best treatm ent, This treatment consistently reduced yellowing for up to 5 days. A decrease in the FvFm ratio may be a useful indicator of broccoli flor ets response to hot water treatments.