Review of Dense Phase Carbon Dioxide Application to Citrus Juices

The United States is the second largest citrus producer in the world. Florida and California are the two major producing states. While oranges from California are mainly used for fresh fruit consumption, more than 90% of oranges produced in Florida are processed to juice (FAO 2008). Consumers demand high quality and convenient products with natural flavor and taste, and appreciate the “fresh” perception of minimally processed juices. They also look for safe, natural, and healthy products without additives and preservatives. New processing technologies promise to meet all these demands without compromising food safety.

Commercial orange juice is thermally processed to inactivate pectinesterase (PE) and spoilage organisms. Active PE causes clarification of orange juice by cloud loss, which is considered a quality defect (Boff et al. 2003). Thermal processing can be detrimental to the organoleptic and nutritional qualities of the juice (Sloan 1995), so the development of non-thermal technologies (Barbosa-Canovas et al. 1998) is desirable in the citrus juice industry.

Dense phase carbon dioxide (DPCD) is a non-thermal technology that can inactivate certain micro-organisms and enzymes at temperatures low enough to avoid the thermal effects of traditional pasteurization. This technology relies on the chemical effect of CO₂ on micro-organisms and enzymes. DPCD pasteurization technology is commercially available. Most of the commercialization efforts so far have been from Praxair Inc. (Burr Ridge, IL). Based on technology licensed from the University of Florida (Balaban et al. 1988, 1998), Praxair developed a continuous system which uses the DPCD process as a non-thermal alternative to thermal pasteurization (Connery et al. 2005). This system has been commercialized under the Trade Mark “Better Than Fresh (BTF).” To date, Praxair has constructed four mobile BTF units for processing about 1.5 liters per minute for demonstration purposes. In addition, a commercial scale unit of 150 liters per minute was also constructed (Connery et al. 2005) and tested at an orange juice processing plant in Florida. There are other commercialization efforts. The excellent taste of the juice processed with this new technology was demonstrated in three independent sensory panels that compared juice treated with this system to that of fresh squeezed juice. In all the tests, no difference could be detected.

It is important that CO₂ is completely saturated in the juice if DPCD is to be successful. Saturation (equilibrium solubility) depends on the pressure, temperature, and composition of the juice. Until recently, the exact amount of CO₂ to be used in DPCD processing was unknown since solubility data was unavailable at different pressures, temperatures, and juice compositions, and an excess amount was used. To optimize the use of CO₂ in this non-thermal process, new equipment has been developed to measure the solubility of CO₂ in liquid systems and juices.

The objective of this paper is to present a general review of the applications of DPCD to citrus juices and to introduce the use of new equipment developed at the University of Florida to determine the solubility of CO₂ in citrus juices.

Paper published with permission.