Effect of pH and Temperature on the Yeast Inhibitory Activity of Chitosan

Abstract

The inhibitory effect of chitosan on the growth of Saccharomyces cerevisiae in laboratory liquidmedium (Potato Dextrose Broth, PDB) was investigated at pH 4.5 and 3.5 and at the temperatures of30 and 4°C, respectively. Acetic acid was used for preparation of chitosan solution and for adjustingthe pH. At 30°C, the growth curves were observed for S. cerevisiae grown in PDB at both pH values.However, longer lag time, slower growth rate and lower maximum cell numbers were found for thegrowth at pH 3.5. The survival curves were observed when chitosan solution was added to the media.At pH 4.5, the yeast numbers were reduced by 3.43 and 5.07 log10 after 72 h of exposure to 1 and 2g/l of chitosan. At pH 3.5, 5.98 log10 reduction was obtained in the medium containing 1 g/l of chitosanand no growth was observed in the medium containing 2 g/l of chitosan. The effect of storagetemperature, 4°C, was also investigated for 17 days. The slow growth was exhibited at pH 4.5 andslow reduction (0.54 Log10 reduction) was found for the growth at pH 3.5. Similar to the results at30°C, antifungal effects on the yeast were more pronounced at higher chitosan concentration andlower pH value. The results illustrated that chitosan may be used in combination with temperature andlow pH to inhibit the spoilage yeast contaminated in food products.

Keywords : Acetic acid / Chitosan / pH / Saccharomyces cerevisiae / Temperature