Ultraviolet C irradiation at 0.5 kJ center dot m(-2) reduces decay withoutcausing damage or affecting postharvest quality of star ruby grapefruit (C-paradisi Macf.)

Star Ruby grapefruit [Citrus paradisi (Macf.)] were harvested in November, February, and May, treated with ultraviolet C (W-C) light at 0.5, 1.5, or 3 .0 kJ.m(-2), and then stored at 7 degreesC and 90-95% relative humidity (RH ) for 4 weeks with 1 additional week at 20 degreesC and similar to 80% RH. Untreated fruits were used as control. W-C irradiation at 0.5 kJ.m(-2) effe ctively reduced decay development as compared to nontreated fruit without c ausing damage. Irradiation at dosages >0.5 kJ.m(-2) did not further improve decay control and caused rind browning and necrotic peel, the extent of da mage depending on treatment dosage and harvest date. The percentage of dama ged fruit after irradiation at the higher UV-C dosages was significantly hi gher in fruit harvested in November; differences between fruits harvested i n February and May were negligible. After W-C irradiation, the phytoalexins scoparone and scopoletin accumulated in flavedo tissue, their amounts depe nding on harvest date and UV-C dosage. Both phytoalexins showed similar acc umulation patterns, although the concentrations of scoparone were much lowe r than those of scopoletin: Phytoalexin levels increased in most samples as the treatment dosage increased. No detectable levels of scoparone and scop oletin could be found in nonirradiated fruit. The influence of W-C treatmen ts on soluble solids concentration and titratable acidity of juice was negl igible.