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.
INACTIVATION OF PECTINESTERASE IN ORANGE JUICE BY SUPERCRITICAL CARBON DIOXIDE
Single strength orange juice was treated with supercritical carbon dioxide (CO2) and the effect of process time, temperature and pressure on pectinesterase (PE) activity was determined. PE could be inactivated with supercritical CO2 below temperatures necessary for thermal inactivation. Higher pressure, temperature and longer treatment time resulted in more inactivation. Inactivation kinetics showed activation energy was significantly reduced at SC CO2 treatment at 31 MPa (97.4 KJ/mole), compared to identical treatments at atmospheric pressure (166.6 KJ/mole). D values ranged from 2673 min at atmospheric pressure and 40 degrees C to 10 min at 31 MPa and 60 degrees C. z value at atmospheric pressure was 8.8 C degrees , and at 31 MPa 5.2 C degrees .
LOW PH INACTIVATION OF PECTINESTERASE IN SINGLE STRENGTH ORANGE JUICE
Frozen orange juice concentrate (63.8° Brix) was reconstituted with water to single strength juice and supplemented with a commercial citrus pectinesterase (PE) to give an activity of 1.5 PE units/mL juice. Reconstituted juice and freshly squeezed single strength orange juice were treated with a cation exchange resin. Resin treatment decreased the pH of the juice from 3.75 to 2.0 and completely inactivated PE. PE was also inactivated following acidification of the juice to pH 2.0 with concentrated hydrochloric acid. Very little cloud loss occurred in refrigerated (4°C) juice at pH 2.0 for approximately 12 wk; however, a loss (> 95%) of ascorbic acid resulted. Only microorganisms died-off rapidly (> 99.9%) in juices adjusted to pH 2.0 using ion exchange resin, but not in juices lowered to pH 2.0 with HCl.