Influence of pH regulation. The second continuous fermentation
was performed at 50°C to test pH influence on
biomass and lactic acid production. In order to reduce
inhibition pressure, a new continuous culture at high dilution
rate (0.2 h21) was conducted between pH values of
6.0 –7.0 with 2 g l21yeast extract and 60 g l21 sucrose
(molasses) without ammonium salts. The results show that
optimal pH for lactic acid production is defined around 6.5
(Table 4). Glucose and fructose were not detected for pH
values between 6.2– 6.8, but a very low concentration of
fructose (,2 g l21) was detected for pH values between
6.0 –7.0 (data not shown). Other by-products such as acetate,
pyruvate, ethanol, fumarate, formate, and citrate were
detected at very low concentrations (total ,2 g l21 6 0.5).