Temperature-dependency on the inactivation of Saccharomyces pastorianus by low-pressure carbon dioxide microbubbles

Temperature-dependency on cell membrane injury and inactivation of Saccharomyces pastorianus by low-pressure carbon dioxide microbubbles (MBCO 2 ) was investigated. The number of surviving S. pastorianus cells after MBCO 2 treatment detected with yeast and mould agar (YMA, an optimum agar) was higher than that with YMA adding 2.5 g/L sodium chloride and yeast nitrogen base agar (a minimum agar). However, the decrease of the surviving number by thermal treatment was not changed among above agars used. The fluorescence polarization (FP), which indicated the phase transition of the membrane of S. pastorianus cells treated with MBCO 2 increased with increasing temperature. The activity of the alkaline phosphatase (AP), a periplasmic enzyme, in S. pastorianus cells after MBCO 2 and thermal treatments increased with the FP but was reduced by further increasing temperature. The FP and AP activities after MBCO 2 treatment increased at a temperature lower than the temperature of the thermal treatment. In addition, intracellular pH of S. pastorianus decreased by the MBCO 2 treatment at lower temperature with increasing pressure. Therefore, it was revealed that phase transition of the cell membrane and inactivation of S. pastorianus was caused by MBCO 2 treatment at lower temperature than thermal treatment and that the effect was induced by the dissolved CO 2 and increased with increasing pressure.