The effect of temperature and pH on the growth of lactic acid bacteria: a pH-auxostat study

The growth of Streptococcus salivarius subsp. thermophilus, Lactococcus lactis subsp. lactis, Lactobacillus delbrueckii subsp. bulgaricus, Lactobacillus acidophilus and Lactobacillus paracasei was studied in a pH-auxostat. The computer-controlled smooth change of pH or temperature was used to study the effect of pH and temperature on the culture characteristics (specific growth rate μ, growth yield Y ATP and specific lactate production rate Q ATP). The behaviour of μ and Q ATP with an increase of temperature suggested that ATP production capacity was an important factor in determining the maximum growth rate of lactic acid bacteria (LAB). The decrease of Y ATP with increase of temperature resulted in the decrease of specific growth rate while Q ATP remained constant or even increased. With the decrease of pH, decrease of both Y ATP and Q ATP was observed. S. thermophilus St20 having the highest maximum specific growth rate of 2.2 h −1 at 44 °C was the most acid sensitive strain. The L. paracasei E1H3 having the lowest μ max was the most tolerant strain to pH change. The behaviour of mixed culture of L. bulgaricus and S. thermophilus in milk in a pH-auxostat with pH-decrease was in agreement with the pure culture experiments of the same species. The study showed that pH-auxostat with smooth controlled change of pH and temperature is an effective method for determination of technological characteristics and comparative physiological study of LAB.