CHARACTERIZING ACIDIFICATION KINETICS BY MEASURING PH AND ELECTRICAL-CONDUCTIVITY IN BATCH THERMOPHILIC LACTIC FERMENTATIONS

On-line measurements of pH and electrical conductivity data have made it possible to access time and rate feature points of thermophilic lactic acid fermentations. Ten feature points characterize curves of acidification and conductivity changes using the main points of inflection observed. The presence or absence of urease also changes the observed kinetics and corresponding feature points. These phenomena and the time patterns of the biomass and products permit an understanding of the meanings of the feature points. These points showed the excellent reproducibility of fermentations conducted in standard conditions, with coefficients of variation lower than 5.1% for nine of them. They were also used to compare the effects of the type of starter, temperature and culture medium. The temperature affects the urease activity and acidification optima. The presence of fat (32 g/l) in the medium does not change any feature point, while the presence of sucrose (90 g/l) results in a decrease in the acidification rate and a longer fermentation time.