Influence of modified atmosphere and preservatives on the growth of Zygosaccharomyces rouxii isolated from dried fruits

The influence of water activity (aw), preservatives, modified atmosphere and their combinations on the growth of Z. rouxii was determined by cultivating two strains isolated from raisins and prunes in culture media under different conditions and by counting the colony forming units. Yeast extract glucose broths or agars were adjusted to the desired aw by means of glucose. Preservatives added to the media (0–600 ppm) were either K-sorbate, Na-benzoate or their mixture. Modified atmospheres were carried out by packing culture plates or flasks in plastic bags under different CO2N2 gas mixture. Response surface design was carried out to optimize the growth inhibition of Z. rouxii by the mentioned factors. Although Z. rouxii is osmotolerant, the strains studied could not grow at aw 0.79. They also showed a high tolerance to CO2; even 80% CO2 seems to not inhibit growth. However, CO2 atmosphere at high pHs and low preservative concentrations stimulated yeast growth. At pH 4.0 and under modified atmosphere (80% CO220% N2), no growth was observed at any aw in the range of 0.80–0.90 when using a preservative concentration of 220 ppm Ksorbate or 280 ppm Na-benzoate