Inhibitory effects of eugenol and thymol on Penicillium citrinum strains in culture media and cheese

In the present work we studied the antifungal effect of eugenol and thymol on the growth and production of citrinin from Penicillium citrinum (NRRL 2274 and NRRL 2269) in culture media and in different Spanish cheeses (Arzria-Ulloa, Cebreiro and San Simon). The rate of growth was assessed by measuring colony diameters and the production of citrinin was measured using a rapid semi-quantitative fluorometric technique confirmed by RP-HPLC. A stronger inhibitory effect of eugenol than thymol was evident. 200 mug/ml of eugenol in solid culture medium increased the lag time of growth up to 9 days, and decreased the rate of colony growth. In liquid medium, a complete inhibition of fungal growth was observed. By contrast, thymol in the liquid culture medium only affected the growth rate. In Arzria-Ulloa cheese, 200 mug/ml of eugenol fully inhibited fungal growth, while in Cebreiro cheese no effect was observed for this compound. Regarding the capacity to inhibit mycotoxin production 100 mug/ml eugenol delayed citrinin production until the sixth day, after which a limiting effect persisted. In Arzlia-Ulloa cheese, no citrinin was detected at a concentration of 150 mug/ml of eugenol, but citrinin was detected after 5 days in the case of thymol at the same concentration. In Cebreiro cheese, neither eugenol nor thymol prevented the production of citrinin at the concentrations applied. (C) 2001 Elsevier Science B.V. All rights reserved.