White light prevents increased catechin synthesis by ultraviolet irradiation in banana fruits

Irradiation of green banana fruit (Musa AAA, Cavendish subgroup, ‘Williams’) with an ultraviolet (UV)-C fluence of 720 Jm'2 increased ethylene evolution five-fold compared with controls during the first 24 h in either dark or light. The activity of phenylalanine ammonia-lyase (PAL) in extracts from the outer peel of irradiated fruit increased at least two-fold in either light or dark, but at 20°C it took 1-2 d for PAL activity to increase above the rate in controls. Irradiation did not affect the content of total phenolic compounds in outer peel in either dark or light until 4-6 d later. The content of chlorogenic acid was also not increased in either dark or light by UV-C. The catechin content of outer peel doubled in the dark within 24 h of irradiation and continued to increase six-fold during the first three days after irradiation. Exposure to white light (13.2 Wm 2) after irradiation almost completely prevented this increase in catechin content. These results show a close metabolic relationship between catechin and the bronze pigment previously reported in bananas irradiated with UV-C.