Effects of water activity and temperature on germination and growth profiles of ochratoxigenic Penicillium verrucosum isolates on barley meal extract agar.

The aim of this work was to study the combined effects of water activity (aw, 0.75-0.99), temperature (10-30 degrees C) and isolate on spore germination and mycelial growth of ochratoxigenic Penicillium verrucosum isolates on barley meal extract agar (BMEA). Lag phases prior to germination (h), germination rates (h(-1)) and growth rates (mm day(-1)) were obtained at each set of conditions and for all the isolates. Analysis of variance showed a significant influence of the abiotic factors assayed on fungal development. Minimum aw levels found for germination and mycelial growth were 0.80 and 0.85, respectively, while maximum germination and growth rates were obtained at 0.95-0.99 aw level. Although maximum germination was obtained at 20 degrees C, significant differences were not found between growth rates at 20 and 30 degrees C. Data were modelled by MLR regressions and response surface models were obtained. Spore germination and mycelial growth of ochratoxigenic P. verrucosum isolates are significantly affected by water activity and temperature. Moreover, different isolates may have slightly different response to environmental factors. Predictive models obtained may allow a rough prediction of germination/growth as a function of the storage temperature and moisture content of barley grains.