Aging of immobilized brewing yeast in a continuous bubble-column reactor

The aim of this work was to study the physiological changes of immobilized brewing yeast Saccharomyces cerevisiae in a continuous reactor. Continuous cultivation was carried out at three different temperatures (15, 20 and 25°C) with an industrial brewing yeast strain (UNICER, Bebidas de Portugal, S.A.). During the continuous experiment the viability of free and immobilized cells was followed using vital staining and flow cytometry. The results of viability determination were used to calculate the specific death rate of the immobilized cells (Kd). Further, the flow cytometry was used to follow the glycogen content of cells and the number of budding cells. The experiments showed that the viability of free cells stayed constant in the course of the whole experiment. Conversely, the viability of immobilized cells decreased during the whole time of the cultivation as well as the viability decreased in the direction from the surface to the depth of the biofilm. The study of the immobilized biomass showed that specific immobilized cell death rate (Kd) was a function of cultivation temperature and that the values of Kd increased with temperature. Higher content of glycogen and a lower count of budding cells was found in immobilized cell fraction.