Application of Supercritical Carbon Dioxide for the Preservation of Fresh-Like Carrot Juice

Gabriele Di Giacomo, Francesca Scimia, Luca Taglieri

Supercritical carbon dioxide has been suggested and is under development for non-thermal pasteurization of food and perishable beverages by virtue of its effectiveness in microflora and enzyme inactivation.  In comparison to competitive technologies, it is particularly attractive at industrial scale since the liquids can be continuously processed with recirculating carbon dioxide. One of the most attracting application is the preservation of increasingly interesting fresh-like juices of fruits and vegetables, particularly the low acidic ones like carrot juice, for which the shelf life can be enhanced of about one order of magnitude (from two or three days to about three weeks or more) while maintaining the main characteristics of the fresh squeezed equivalent. Most of this exciting result is directly related to the unique reversible acidification action of this technology. In this study it has been found that Pectin methylesterase and Peroxidase are actually the solely responsible for cloud stability disappearance and off-flavor, browning and other enzymatic-related undesirable changes occurring during the storage of fresh-like carrot juice, under refrigerated conditions. In fact, the level of Polyphenol oxidase activity is very low and the level of fat in this juice is also very low, thereby nullifying the potential negative action of those enzymes that may cause adverse effects by acting on fats.  In this contest, it has been found, using a semi-continuous laboratory apparatus, that a micro-bubbled stream of supercritical carbon dioxide at 313 K, 25 MPa and juice/CO₂ ratio (w/w) equal to 0.33, significantly inactivated the labile isoform fraction of PME (above 70%) and of POD (almost completely) in about one hour. The values of the stable isoform dimensionless activity of the above mentioned enzymes and of the inactivation constant were calculating by fitting experimental data with a plain, semi-empirical equation obtaining the following results: 0.0894 and 0.00345 min^-1 for PME, and 0.1072 and 0.04035 min^-1 for POD.