Abstract
Inactivation of microorganisms and pectinesterase (PE) in fruit juices by supercritical CO2 was investigated. For this experiment, an original device equipped with a mixer for mixing CO2 into juices and a zigzag steel pipe (φ 10 cm × 12 m) for keeping CO2 in a supercritical state (40°C, 100 kg/cm2) was constructed. Four kinds of fruit juice (orange, grapefruit, grape and apple) were treated with this device. When the juices were mixed with CO2 at a rotation speed of 400 rpm, the viable cell count of each juice was reduced to 1/10 of the initial number. In addition, in the orange juice treated at a rotation speed of 800 rpm, viable cell and yeast counts were remarkably reduced to 1/100 and 1/1000 of the initial values, respectively. Residual activities of PE in each juice treated by supercritical CO2 decreased by values varying from 0 (grape) to 34% (apple) when treated at a rotation speed of 400 rpm. The sugar, organic acid and free amino acid contents of orange juice treated by supercritical CO2 at a rotation speed of 800 rpm were approximately equal to those of non-treated juice. When treated orange juice was stored at 5°C, the quality of juice was maintained at a high level for 21 days.
