Influence of pH, temperature and initial yeast:bacteria ratio on the stimulation of Lactobacillus hilgardii by Saccharomyces florentinus isolated from sugary kefir grains.

The effects of pH, temperature and initial yeast:bacteria ratio on Lactobacillus hilgardii and Saccharomyces florentinus cultivated either in pure or mixed culture were studied. Quadratic polynomial as a function of factors was proposed to express the lactic acid production at different sampling times, and the percentage increase in lactic acid production by Lact. hilgardii in mixed culture compared with pure culture. Temperature was the factor which had the main influence on lactic acid production in mixed culture, whereas stimulation of bacteria depended greatly on pH value. In the range 0.1-20%, the initial yeast-bacteria ratio had no effect on these responses, but presence of the yeast was absolutely necessary to obtain high production of lactic acid. Optimum culture conditions were determined to maximize these characteristics.