Influence of water activity and temperature on conidial germination and mycelial growth of ochratoxigenic isolates of Aspergillus ochraceus on grape juice synthetic medium.: Predictive models

The first stages in the development of Aspergillus ochraceus, an ochratoxin A-producing fungus that infects grapes and may grow on them, have been studied on a synthetic nutrient medium similar to grape in composition. Spore germination and mycelial growth have been tested over a water activity (a(w)) and temperature range which could approximate to the real conditions of fungal development on grapes. Optimal germination and growth were observed at 30 degrees C for all three isolates tested. Maximal germination rates were detected at 0.96-0.99 a(w) at 20 degrees C, while at 10 and 30 degrees C the germination rates were significantly higher at 0.99 a(w) Although this abiotic factor (a(w)) had no significant influence on mycelial growth, growth rates obtained at 0.98 a(w) were slight higher than those at other a, levels. Predictive models for the lag phase before spore germination as a function of water activity and temperature have been obtained by polynomial multiple linear regression, and the resulting response surface models have been plotted. (c) 2005 Society of Chemical Industry.