Influence of pH on the Fungitoxic Activity of Naturally Occurring Compounds.

The optimum pH for growth for eight toxigenic strains of Aspergillus was recorded at pH 6 in unamended potato dextrose broth medium. Significantly less mycelial growth was observed at pH 4 and 8, respectively, for all of the fungal strains. In the presence of 1.0 mM of thymol, mycelial growth was completely inhibited at pH 4, 6, and 8 for all of the fungal strains. Carvacrol, at the same concentration, completely inhibited the growth of the fungi only at pH 4 and 8. At lower concentrations (0.1 and 0.5 mM), in the presence of thymol or carvacrol, partial mycelial inhibition at all pH levels was observed with significantly less mycelial growth at pH 4 and 8.