Effect of preservatives, tween 20, oil content and emulsion structure on the survival of Lactobacillus fructivorans in model salad dressings

The effect of potassium sorbate (PS), nisin, Tween® 20 and oil level on the survival of Lactobacillus fructivorans in model salad dressings was studied. In general, L. fructivorans growth was prevented in formulated emulsions, but the addition of nisin was necessary to inactivate the bacterium throughout the storage time evaluated. The bacteriocin activity showed to be strongly dependent on system composition. Addition of PS alone did not influence L. fructivorans survival. But, when this preservative was added together with nisin to an emulsion containing 110 g/kg of oil, it exerted an antagonistic action on nisin effectiveness while for other levels of oil, a synergistic action was verified. The increase of oil level did not affect L. fructivorans survival in those emulsions without nisin. However, when the bacteriocin was present, it produced different effects which depended on system composition. Addition of tween did not affect L. fructivorans survival for emulsions free of additives or containing as preservative only PS. However, when nisin was present, the emulsifier effect was entirely dependant on oil content. Furthermore, the structure of the food matrix appeared as an additional factor which could influence either the growth of the microorganisms or the functionality of the preservatives. Tween addition turned the systems more fluid or solid, depending on the oil content of the systems considered. Results obtained highlight the importance of considering ingredient interactions when evaluating microbial stability of food systems.