Pulsed white light in combination with UV-C and heat to reduce storage rot of strawberry

Three physical methods-pulsed white light, heat, and ultraviolet-C (UV-C, lambda = 254 nm) irradiation-were used in different combinations for surface decontamination of strawberry fruit. Strawberries were inoculated with conidia of Botrytis cinerea. Over 10 days, fungal development and structural damage (e.g. holes, changes in fruit firmness) were daily recorded. Pulsed light treatments consisted of 30 mus pulses at a frequency of 15 Hz for a total duration of 40 to 250 s. For the combination experiments, the UV-C doses were 0.5 or 1.0 U m(-2) and the heat treatments were at 40 and 45degreesC for 3 or 15 min. Pulsed light treatments alone had no positive or negative effect. Combining a thermal and an UV-C treatment allowed for a decrease of the thermal treatment to 40degreesC for the same level of fungal inactivation. No external fruit damage was reported at this temperature of 40degreesC. A combination of a thermal treatment with light pulses did not result in a significant difference in fungal growth. Combining two illumination treatments did not cause a significant decrease in fungal development. In both cases, however, the period before the first observation of fungal growth was increased by I or 2 days. Induced resistance against fungal infections in treated fruit was not observed after pulsed light treatment. These induced reactions of treated berries were observed after UV-C treatment of strawberries, but not observed when a thermal treatment was used. (C) 2002 Elsevier Science B.V. All rights reserved.