Unfolding of Poly-L-glutamic Acid by Microbubbling of Supercritical Carbon Dioxide
The conformational changes in α-helical poly-L-glutamic acid caused by microbubbling supercritical CO2 were investigated with circular dichroism spectra. After microbubbling using a micropore filter at 35 and 30 MPa for 30 min, α-helix content decreased to 37%, while without the filter it was 68%. The α-helix structure was significantly decomposed by a high density of CO2. No important changes were observed in heating, autoclaving, or pH-lowering.
pH-Defining Equilibrium between Water and Supercritical CO2. Influence on SFE of Organics and Metal Chelates
A direct measurement of the pH of water in contact with supercritical CO 2 was made by observing the spectra of a pH indicator with a UV-vis spectrophotometer. The pH was analyzed under pressures of 70-200 atm and temperatures of 25-70 °C. The measured pH varied from 2.80 to 2.95, and relative standard deviations of <1.5% were achieved. The effects of pH on the efficiency of supercritical fluid extraction of metals and ionizable organic species in water-containing systems are discussed.
INACTIVATION OF MICROORGANISMS BY CARBON DIOXIDE UNDER PRESSURE
Carbon dioxide under pressure killed bacteria, molds, and yeast. The effect was synergistic with raised temperature and acidic pH and antagonized by lowered Aw. Time of exposure was important, and conditions needed for the inactivation of different microbes varied, some organisms being much more resistant than others. The effect was tested on various foods, but disrupted the texture of some. Clostridial spores were very recalcitrant, but could be destroyed by further lowering the pH along with concurrent exposure at 70°C. The pH in media under pressure was measured and theories advanced for the antimicrobial effect.