22 UV-B irradiation was applied to broccoli florets to investigate its effect on 23 chlorophyll degradation and chlorophyll-degrading enzyme activities in stored broccoli. 24Broccoli florets were irradiated with UV-B doses at 4.4, 8.8 and 13.1 kJ m -2 and then 25 kept at 15 ºC in darkness. We found that a UV-B dose of at least 8.8 kJ m -2 efficiently 26 delayed the decrease of the hue angle value and the contents of chlorophylls a and b. 27Chlorophyllide a and 13 2 -hydroxychlorohyll a gradually decreased with senescence. 28Pheophorbide a and pyropheophorbide a levels were significantly higher in broccoli 29 without UV-B treatment. Chlorophyllase and chlorophyll-degrading peroxidase activities 30 with UV-B treatment were suppressed, as well as the activity of Mg-dechelatase. Mg-31 dechelating substance activity was also suppressed with this treatment. We concluded 32 that UV-B treatment effectively suppressed chlorophyll degradation in broccoli florets 33 during storage, suggesting that the effect could be due to the suppression of chlorophyll-34 degrading enzyme activities.

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The effects of heat treatment on the formation of chlorophyll (Chl) derivatives and Chl-degrading enzyme activities in stored broccoli (Brassica oleracea L. Italica Group 'Ryokutei') florets were determined. The Chl a level barely changed during heat treatment, but each Chl a derivative level changed. Chlorophyllide (Chlide) a, pheophorbide (Pheide) a, C13 2 -hydroxychlorophyll (C13 2 -OHChl) a, Chl a', an isomer of Chl a, and pheophytin (Phy) a were detected as a Chl derivative during heat treatment and during storage after treatment. Chlide a, Pheide a, and C132 -OHChl a levels decreased during 2-h heat treatment (50°C), whereas Chl a' and Phy a levels increased. Chldegrading enzyme activities, in particular, Mg-dechelation activity, were effectively suppressed after 2 h of heat treatment. The content of Chls a and b in control broccoli florets decreased greatly during storage at 15°C, while the content in heat-treated broccoli florets hardly changed at all. In Chl derivatives, the Pheide a level in broccoli florets treated with or without heat treatment, especially the former, increased appreciably during storage. The Chlide a level in control florets decreased markedly during storage. On the other hand, the Chlide a level in heattreated broccoli florets did not change during storage. Mg-dechelation activity in control florets markedly increased after 4 days of storage at 15°C, but the enhancement of the activity was suppressed by heat treatment. These findings suggest that Chl derivatives, especially Pheide a, are accumulated as intermediates in heat-treated broccoli florets, and Mg-dechelating action, in conjunction with that of chlorophyllase and Chl-degrading peroxidase, could be involved in Chl degradation in stored broccoli florets.