Sterilization of Microorganisms with Supercritical Carbon Dioxide

The sterilizing effect of supercritical carbon dioxide (SC-CO₂) is described as compared with gaseous CO₂(G-CO₂) and liquid CO₂(L-CO₂). Baker's yeast, Escherichia coli, Staphylococcus aureus and conidia of Aspergillus niger were sterilized by treating with SC-CO₂ at 200 atm and 35°C when the water content of each microorganism was 70~90%. However, dry cells with a water content of 2 ~ 10% could not be sterilized under the same conditions. No sterilizing effect from SC-CO₂ on endospores of Bacillus subtilis and B. stearothermophilus was observed. G-CO₂ and L-CO₂ produced no sterilizing effect against both wet and dry baker's yeast cells, while wet E. coli cells were sterilized with G-CO₂. Although dry conidia of A. niger could not be sterilized with SC-CO₂ alone, the addition of ethanol or acetic acid to SC-CO₂ made it possible to sterilize these. Without any decrease in their enzymatic activities, E. coli and baker's yeast in a-amylase and lipase preparations were sterilized with SC-CO₂.