Comparison of a two-stage system with low pressure carbon dioxide microbubbles and heat treatment on the inactivation of Saccharomyces pastorianus cells

To clarify how Saccharomyces pastorianus cells were affected by a two-stage system that was heating and pressurizing after microbubbled carbon dioxide (MB-CO2) was mixed with the S. pastorianus suspension at low temperature and pressure (two-stage MB-CO2), S. pastorianus cells were observed by electronic microscopy and stained with propidium iodide (PI). Furthermore, the amounts of nucleic acid and protein leaked from treated S. pastorianus cells were determined and intracellular enzyme activities were measured. It was observed by scanning electric microscopy that wrinkles in S. pastorianus cells treated by two-stage MB-CO2 with a heating coil at 50 °C (MB50) and heat treatments at 50 °C and 80 °C (H50 and H80) were more than those in untreated (NT) cells. Upon observation with transmission electron microscopy, it suggested that MB50 had a direct effect on the intracellular substrate, although little influence on the membrane, whereas H80 cells showed visible damage to cell membranes. However, it was recognized that PI intensity in MB50 cells was great than that in NT, H50 and H80 cells, and that the amount of nucleic acid and protein leaked from H80 cells was significantly higher than that of NT, MB50 and H50 cells. Furthermore, the enzyme inactivation efficiency in MB50 cells was the same as in H80 cells. These results estimate that inactivation of S. pastorianus by two-stage MB-CO2 was due to actions of MB-CO2 on the cell membrane and the intracellular substrate such as enzyme inactivation.