The effect of potassium sorbate, NaCl and pH on the growth of food spoilage fungi

Abstract

In this study, the hurdle technology approach was used to prevent fungal growth of common spoilage fungi in naturally fermented black olives (Alternaria alternata, Aspergillus niger, Fusarium semitectum and Penicillium roqueforti). The factors studied included a combination of different concentrations of potassium sorbate (100 up to 1000 mg/L), a range of pH values (4.5, 5, 5.5, 6, and 6.5) and levels of NaCl (0, 3.5, 5, 7.5, and 10%). Alternaria alternata was the most sensitive fungus whereas P. roqueforti was the most resistant fungi against all hurdle factors. The combination of all hurdles completely inhibited A. alternata and F. semitectum by lowest inhibitory factors, such as 100 mg/L potassium sorbate with 3.5% NaCl at pH 5. On the other hand, at pH 5, A. niger and P. roqueforti were totally prevented by a combination of 300 mg/L potassium sorbate with 10% NaCl and 400 mg/L potassium sorbate with 7.5% NaCl, respectively. Potassium sorbate and 5-10% NaCl interaction had significant stimulation effect on P. roqueforti and A. niger (p < 0.05). This study indicates that potassium sorbate is a suitable preserving agent to inhibit growth of fungi in fermented products of pH near 4.5 regardless levels of NaCl. For products of slightly higher pH, the addition of potassium sorbate is suggested in combination with NaCl.