Effects of salts on Debaryomyces hansenii and Saccharomyces cerevisiae under stress conditions

The effect of Na+ and K+ on growth and thermal death of Debaryomyces hansen ii and Saccharomyces cerevisiae were compared under stress conditions as th ose commonly found in food environments. At the supraoptimal temperature of 34 degrees C both cations at concentrations of 0.5 M stimulated growth of D. hansenii, while K+ had no effect and Na+ inhibited growth of S. cerevisi ae. At 8 degrees C, close to the minimum temperature for growth in both spe cies, both cations inhibited both yeasts, this effect being more pronounced with Na+ in S. cerevisiae. At extreme pH values (7.8 and 3.5) both cations at concentrations of 0.25 M stimulated B. hansenii while Na+ inhibited S. cerevisiae. K+ inhibited this yeast at pH 3.5. Thermal inactivation rates, measured at 38 degrees C in D. hansenii and at 48 degrees C in S. cerevisia e, decreased in the presence of both cations. This protective effect could be observed in a wider range of concentrations in D. hansenii. These result s call the attention to the fact that not all yeasts have the same behaviou r on what concerns synergy or antagonism of salt together with other stress factors and should be taken into consideration in the establishment of foo d preservation procedures. (C) 2000 Elsevier Science B.V. All rights reserv ed.