Effect of benzoic Acid on growth yield of yeasts differing in their resistance to preservatives.

Yeasts grown in the presence of benzoic acid tolerated 40 to 100% higher benzoic acid concentrations than did those grown in the absence of weak-acid-type preservatives. They also accumulated less benzoate in the presence of glucose. In chemostat cultures, benzoic acid reduced growth yield and the rate of cell production but increased specific fermentation rates. Benzoate contents were lower than those required for equilibrium when cells were impermeable to benzoate anion. Intracellular pHs were maintained near neutrality. Between species, stimulation of fermentation was inversely related to preservation resistance but was unrelated to the maximum rate of fermentation. The results show that a major effect of benzoic acid on yeasts in the presence of an energy source is the energy requirement for the reduction in cytoplasmic benzoate concentration and maintenance of pH. This energy source is unavailable for growth, resulting in lower growth yields and rates. Resistant species may be less permeable to undissociated benzoic acid.