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The antifungal activity of polygodial, which was isolated from Polygonum hydropiper used as a hot spice in Japan, was investigated through measuring its MICs and against food-contaminants including 4 strains of Saccharomyces cerevisiae, 3 strains of Zygosaccharomyces species, and 5 strains of Aspergillus species. All yeast-like fungi exhibited strong antifungal susceptivilities with MICs and MFCs below 3.13$\mu$g/ml. Strains of Aspergillu species showed moderate with MIC of 25-50$\mu$g/ml and MFC of 50-100$\mu$g/ml. However these strains to sorbic acid, as already known, revealed very weak with MICs of 200-800$\mu$g/ml and MFCs above 1600$\mu$g/ml. In addition, effects of various pHs and temperatures on the antifungal activity of polygodial were tested against S. cerevisiae. At 4$\circ$C, the fungicidal activity of polygodial gradually increased with incubation time and reached the maximum(MFC of 3. 13$\mu$g/ml) in 5 hours. At temperatures in the range of 30-45$\circ$C, the activity of polygodial increased in proportion to temperature rise and in particular at 45$\circ$C was possible with the concentration of 0.1$\mu$g/ml. mOn the other hand, medium pH was also identified to affect the antifungal activity of polygodial. Namely, compared to neutral (pH7), acidic(pH 3) and basic(pH 9) medium synergized its activity (MIC and MFC) to 8- and 2- fold, respectively.
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