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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1Pheophytinase (PPH) activity and gene expression of chlorophyll (Chl)-degrading 2 enzymes relating to UV-B treatment in postharvest broccoli (Brassica oleracea L. Italica 3 Group) florets were determined. PPH is involved in the dephytylation of Mg-free Chl a, 4 pheophytin (Phy) a. However, chlorophyllase (Chlase, EC.3.1.1.14) also uses Phy a as a 5 substrate to produce pheophorbide (Pheide) a by dephytylation. For an accurate 6 determination of PPH activity, the PPH protein fraction was separated from Chlase protein by 7 ammonium sulfate precipitation. The protein precipitated by 45-60% saturated ammonium 8 sulfate was included a little bit Chlase activity and was suitable for PPH determination.

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