Inactivation of conidia of Botrytis cinerea and Monilinia fructigena using UV-C and heat treatment

The effect of UV-C (lambda = 254 nm) and heat treatment was investigated on the inactivation of conidia of Botrytis cinerea and Monilinia fructigena, two major postharvest spoilage fungi of strawberries and cherries, respectively. Both fungi were grown at 21 degreesC in the dark and conidia were isolated after 1 week by washing the mycelium with a mild detergent solution. After Filtration and resuspension in phosphate buffer to a titer of 10(5) to 10(6) cfu/ml, the conidia were subjected to different treatments. The applied 2 UV-C doses varied from 0.01 to 1.50 J/cm(2), and the conditions for the thermal treatment were 3, 5, 10, 15 and 20 min at temperatures ranging from 35 to 48 degreesC. Both techniques were applied individually and in combination. Spore inactivation increased with increasing intensity of single treatments. No surviving spores of B. cinerea were observed after 15 min at 45 degreesC or an UV-C treatment of 1.00 J/cm(2). M. fructigena was more sensitive and a thenrial treatment of 3 min at 45 degreesC or an UV-C treatment of 0.50 J/cm(2) resulted in complete spore inactivation. Combination of both techniques reduced the required intensity of the treatment for inactivation of both fungi. The order of the applications had a significant effect on the degree of inactivation. The inactivation of B. cinerea conidia was greater when the heat treatment came first, and for M. fructigena, most inactivation was achieved when the heat treatment was preceded with an UV-C irradiation. (C) 2002 Elsevier Science B.V. All rights reserved.