Short-term heat conditioning of grapefruit to alleviate irradiation injury

'Marsh' white grapefruit (Citrus paradisi Macf.) harvested from exterior ca nopy positions were less tolerant of 0.5 or 1.0 kGy irradiation than were i nterior fruit. Irradiation at 0.0, 0.5, or 1.0 kGy resulted in 0.0%, 24.3%, and 37.5% surface pitting of fruit, respectively. Fitting was reduced 30% by temperature conditioning with vapor heat at 38 or 42 degrees C for 2 hou rs. Exterior canopy fruit had approximate to 2-fold more pitting, had great er weight loss, and were firmer than interior canopy fruit. Fruit weight lo ss increased and firmness decreased as conditioning temperature and irradia tion dose increased. Total soluble solids, titratable acidity, and flavor d ecreased with increasing irradiation dose. The peel of exterior canopy grap efruit was damaged more by irradiation than was that of interior fruit, but irradiation damage was reduced by temperature conditioning.