Факторы, влияющие на поверхностный электрический заряд дрожжевых клеток Saccharomyces cerevisiae

The adsorption capacity of yeast cells can partially solve the problem of colloidal instability of beer. It is believed that an increase in the amount of adsorbed colloidal particles can be achieved by increasing the negative charge of the cells. The electric charge on the cell surface is due to the molecular composition of the cell wall, mainly the functional groups of the outer layer of mannoprotein - phosphate, carboxyl, and amino groups. Based on the data obtained by X-ray photoelectron spectroscopy, it was shown that the charge on the cell surface is determined by the concentrations of surface phosphorus and nitrogen, as well as their ratio. Generally, bottom-fermentation strains are characterized by higher surface phosphorus concentrations and lower N/P ratios; the opposite is exact for top-fermentation strains. On the other hand, physicochemical environmental factors also affect the electric charge of cells. The influence of factors such as pH, the time of the fermentation process, aeration of the wort, and the addition of free phosphorus into the culture medium was revealed. So, with a decrease in pH, the electric charge, or the zeta-potential characterizing, it becomes more positive. Since a decrease in pH is observed during fermentation, the electric charge also becomes more positive with the course of the fermentation process. Aeration, the addition of free phosphorus, and an increase in the initial density of the wort, on the contrary, increase the negative charge of cell. Finally, an increase in the number of fermentation cycles leads to a change in the electric charge in the direction of positive values. According to the data presented, it can be concluded that by varying the mentioned factors, it is possible to achieve an increase in the negative charge on the cell surface of the yeast. However, to confirm the assumption of an increase in colloids extracted by adsorption due to an increase in the negative charge of cells, further experimental studies of this issue are required.