ONLINE INDIRECT MEASUREMENTS OF BIOLOGICAL VARIABLES AND THEIR KINETICS DURING PH CONTROLLED BATCH CULTURES OF THERMOPHILIC LACTIC-ACID BACTERIA

Fermentations using pure and mixed cultures of Streptococcus salivariu s subsp. thermophilus 404 and Lactobacillus delbrueckii subsp. bulgari cus 398 were performed at controlled pH, by means of a sodium hydroxid e addition. Linear correlations between the substrate (lactose) and th e products (galactose and lactic acid) concentrations and the equivale nt sodium hydroxide concentration have been established. The relations hips obtained from a statistical analysis were related to yield coeffi cients. As she sodium hydroxide weight measurements were continuously and reliably available, their use allowed the implementation of on-lin e indirect measurements of the lactose, galactose and lactic acid conc entrations during the pure and mixed culture controlled pH fermentatio ns. The lactose consumption rate and the lactic acid and galactose pro duction rates were also obtained from on-line sodium hydroxide weight measurements. The agreement between the experimental and the calculate d concentrations and rates of change was also studied.