DESIGN AND TESTING OF AN APPARATUS TO MEASURE CARBON DIOXIDE SOLUBILITY IN LIQUID FOODS
Carbon dioxide (CO2) is a non-toxic, inexpensive, chemically inert, non-flammable fluid and a safe solvent. It has multiple applications in the beverage industry, such as carbonation, and dense phase carbon dioxide (DPCD) technology, a cold pasteurization process.
The solubility of CO2 in water depends on pressure and temperature (Dodds and others 1956). Increasing pressure increases solubility of CO2 and increasing temperature decreases it. In addition, the presence of other dissolved substances could have a positive or negative effect in CO2 solubility (Meyssami and others 1991). DPCD is a continuous cold pasteurization method that affects microorganisms and enzymes under pressures below 50 MPa (7,250 psi) without the use of high temperature treatments. Currently, the use of CO2 in DPCD treatments is not optimized, since solubility of CO2 in liquid foods at different temperatures, pressures, and compositions is not known. Therefore, excess CO2 is used to assure saturation. If CO2 solubility could be predicted at any temperature, pressure and composition for a liquid food, then the amount of CO2 used would be slightly above this theoretical value, and the process would be more economical. The first step towards this type of prediction is the experimental measurement of CO2 solubility in model liquid food systems; and its correlation with pressure, temperature and composition. Therefore, the objectives of this study were: 1) to design, build and test a high-pressure carbon dioxide solubility apparatus, 2) to compare the volume of CO2 that dissolves in pure water with the current literature; and finally 3) to determine the maximum amount of CO2 in solution with model liquid foods of known composition (binary solutions of fructose and malic acid).
An experimental system to measure the CO2 solubility was designed and tested. The pressure and temperature were controlled in the system, and the design assured an accurate measurement of solubility.
Experimental results of CO2 in solution in pure water were compared with the literature, and there was no significant difference at pressures of 7.56 MPa (1100 psi) and 10.3 MPa (1500 psi), at a constant temperature of 40ºC. By increasing the concentration of fructose or malic acid, solubility of CO2 decreased significantly.
This equipment design and method can experimentally measure CO2 solubility in real liquid foods, and therefore is a significant contribution to the DPCD field. This is the first step in the generation of experimental data for the thermodynamic modeling of CO2 solubility in liquid foods.