Environmental factors affect efficacy of some essential oils and resveratrol to control growth and ochratoxin A production by Penicillium verrucosum and Aspergillus westerdijkiae on wheat grain

This study determined the efficacy of three essential oils (bay, clove and cinnamon oil) and the antioxidant resveratrol (0-500 mu gg(-1)) on the control of growth and ochratoxin A (OTA) production by Penicillium verrucosum and Aspergillus westerdijkiae ( = A. ochraceus) under different water activity (a,, 0.90, 0.95, 0.995), and temperature (15, 25 degrees C) conditions on irradiated wheat grain. The most effective treatment (resveratrol) was then tested on natural grain. The ED50 values for growth inhibition by the oils were 200-300 mu gg(-1) at the a, and the temperatures tested. For resveratrol, this varied from < 50 mu gg(-1) at 0.90-0.95 a(w) to > 350 at 0.995a(w) at both temperatures. The ED50 values for the control of OTA were slightly lower than for control of growth, with approx. 200 mu gg(-1) required for the oils and 50-100 mu gg(-1) of the antioxidant, at 0.90/0.95a(w) and both temperatures. In wet grain (0.995a(w)), higher concentrations were required. For growth there were statistically significant effects of single-, two- and three-way interactions between treatments except for concentration x temperature and concentration x temperature x essential oil/antioxidant treatment. For OTA control, statistically significant treatments were a(w) temperature x a(w) Concentration x temperature, treatment x concentration, and three-way interaction of concentration x a, x treatment for P. verrucosum and A. westerdijkiae. Subsequent studies were done with the best treatment (resveratrol, 200 mu gg(-1)) on natural wheat grain with either P. verrucosum or A. westerdijkiae at 0.85-0.995a(w) and 15/25 degrees C over 28 days storage. This showed that the populations of the mycotoxigenic species and OTA contamination could be reduced by > 60% by this treatment at the end of the storage period. (C) 2008 Elsevier Ltd. All rights reserved.