Evaluation of the effects of salt, potassium sorbate, nisin and lysozyme on the probability of growth of Clostridium sporogenes

The safe preservation of new generation foods (high moisture, low acidity and ambient shelf-stable foods) is microbiologically challenging. The growth of Clostridium botulinum in low acid foods is a hazard for consumers. The aim of this study was to evaluate the combined effect of salt (sodium chloride) (0-8 %w/v), sorbate (potassium sorbate) (0-4.5 %w/v), nisin (0-500 ppm) and lysozyme (0-500 ppm) on the survival of Cl. sporogenes as a non-toxigenic surrogate of Cl. botulinum in terms of the probability of growth by using a central composite rotatable design (CCRD). An additional aim was to observe how the combination of preservatives could reduce the level of required salt to inhibit the growth of Cl. sporogenes. The results indicated that salt and sorbate were the most effective factors in preventing the growth of Cl. sporogenes in high moisture (> 95%) and low acid conditions (pH 7). The probability of growth of Cl. sporogenes in broth was reduced by combinations of salt and sorbate. As expected, a combination of salt and sorbate was more effective than using either of them individually. Nisin and lysozyme had insignificant effects on the probability of growth of Cl. sporogenes (p>0.05). Lysozyme individually and in combination with nisin had no inhibitory effect on Cl. sporogenes. In overall, the addition of sorbate and lysozyme may allow the salt concentration to be reduced while preventing growth.