SupercriticalCarbon Dioxide Micro-Bubble

Advances in the apptication of supercritical (SC), gaseous (G), and ]iquid (LQ) C02 hayc been made regarding the interaction with biological materials or organisms. There are sevcral reports dealing with the influences of SC, G, and LQ C02 on proteins,i'2) amino acids,i) enzymes,3'S) and microbial eells.b'7) Kamihara et aL have described that wet cells (water content of 70-90g,h) of baker's yeast, Evcherichia coli, Stcrphylococcus aureus and conidia of Aspergiilus niger cou]d be sterilizcd by trcating with SC C02 at 35nC and 200 atm for 2h.6) Nakamura et aL havc reported that wet cells of baker's yeast wcre dcstroyed after being trcated with C02 at 40iC and 40atm for morc than 3h,7) The eMciency of sterilization, howeyer, was insuMcient, bccause it was nccessary to prolong the treating time. In our previous papcr, some kinds of enzyrnes in aqueous solutions could be effbctively inactivated by the SC C02 micro-bubble method in only 30min.S) The purpose of this paper is to clar{fy thc effectiveness of thc SC C02 microbubble method for sterilizing microorganisms. Lactohacillus brevis and Saccharoinyces cerevisiae wcre used as thc test microorganisms, These microorganisms werc suspended in physiological saline at the level of 106 CFUi'ml and subjectcd to several C02 treatments with Milton Roy X-10 system (Riviera Bcach, FL). This system was equipped with a 120-ml trcatment vessel incorporating a cylindrical filter (10ptm pore size) made of porous stainless steel for feeding C02. In each experiment, 1OO ml of a sample solution was loaded into the trcatment vessel. Until the pressure had reached the cxperimentaHevel, C02 was fed at 4.0g/min for about lemin, and then the flow was stopped. At the end of the tratment, the vessel was depressurized by slowly opening the pressure-regulating valve over a period of about