Combined effects of weak acid preservatives, pH and water activity on growth of Eurotium species on a sponge cake.

The combined effects of weak acid preservatives (sorbate, benzoate and propionate), pH (6.0, 7.5) and water activity (a(w)) levels (0.80, 0.85, 0.90) on growth of four Eurotium species isolated from bakery products on a sponge cake analogue were studied. Even though it is universally known that these preservatives are much more effective at lower pH values, we chose a 6-7.5 level to correlate with the pH of the Spanish cake product studied. In general, 0.3% doses of all three preservatives were effective only when they were applied at pH 6.0 and at 0.80-0.85 a(w). Potassium sorbate was clearly the most effective in inhibiting growth of all isolates. Under the conditions tested, application of all three preservatives added at 0.03% acted as growth promoter of all isolates rather than having a preservative effect.