Relationship between intracellular protein denaturation and irreversible inactivation of Saccharomyces pastorianus by low-pressure carbon dioxide microbubbles.

To clarify the relationship between irreversible inactivation and intracellular protein denaturation of Saccharomyces pastorianus by low-pressure carbon dioxide microbubbles (CO MB) treatment, a storage test of S. pastorianus cells treated with CO MB was performed, and the effect on the intracellular protein was investigated. In the storage test, the S. pastorianus population, which decreased below the detection limit by CO MB treatment at a temperature of 45 and 50°C (MB45 and MB50), and thermal treatment at a temperature of 80°C (T80), remained undetectable during storage for 3 weeks at 25°C. However, 4.1 and 1.3-logs of the S. pastorianus populations, which survived after CO MB treatment at temperatures of 35 and 40°C (MB35 and MB40), increased gradually during storage for 3 weeks at 25°C. Insolubilization of intracellular proteins in S. pastorianus increased with increasing the temperature of CO MB treatment. Activity of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) identified as one of the insolubilized proteins increased at MB35 and MB40 than non-treatment but disappeared at MB45 and MB50, and T80. Therefore, it was revealed that S. pastorianus cells inactivated below the detection level by CO MB treatment did not regrow and that the denaturation of intracellular proteins of S. pastorianus was caused by CO MB and thermal treatments. Furthermore, it was suggested that denaturation of intracellular vital enzymes was an important factor for achieving irreversible inactivation of S. pastorianus by CO MB and thermal treatments.