EFFECTS OF SUPERCRITICAL CARBON DIOXIDE ON SOME QUALITY ATTRIBUTES OF SINGLE STRENGTH ORANGE JUICE
The retention of cloud in orange juice during storage and distribution is important to the citrus processing industry. Orange juice clarification has been extensively studied. It has been shown that the cloud loss is mainly due to the activity of the enzyme pectinesterase. Attempts in the past have been made to stabilize cloud using different methods that either inactivate pectinesterase and/or stabilize the cloud. Three general methods include (1) heat treatment; (2) chemical addition such as pectic acid hydrolysates, oligalacturonic acids, pectolityc enzymes, and clouding agents; and (3) the lowering of pH with resins and hydrochloric acid. All these methods have side effects on the quality of the juice. Heat treatment affects flavor and aroma compounds, and the addition of foreign compounds is not only undesirable but also forbidden by law.
A new method to inactivate pectinesterase using supercritical (SC) carbon dioxide (CO2) was introduced. The objective of this study was to measure the effects of SC CO2 on pH, total soluble solids (oBrix), total acidity, ascorbic acid, cloud, pectinesterase activity, color and total plate count of the microflora of orange juice. Orange juice was subjected to pressures between 7.4 and 34 MPa, and to temperatures between 35 and 60oC, for times ranging from 15 to 240 minutes. When dissolved in water, CO2 forms carbonic acid, thereby lowering the pH and, presumably, inactivating pectinesterase.
The results obtained showed 100% inactivation of pectinesterase at certain combinations of pressure, temperature, and time. Cloud was not only retained but enhanced and stabilized as well. Cloud was stabilized even when more than 50% of residual pectinesterase was present. The color of the juice was improved slightly, and the ascorbic acid was retained up to 95.2%. The total soluble solids and pH after the treatment did not differ significantly (p < 0.05) from the initial values. The total acidity of the juice decreased slightly, while the brix/acid ratio increased. One of the most important contributions of the supercritical treatment was the sterilizing effect on the microorganisms of the juice.