Study of a control methodology of orange juice evaporation by dielectric spectroscopy

Industrial Plants of concentrated citrus juice work with powerful evaporators with high production capacity, in a complex conformation in order to save the maximum energy and the preservation of thermolabiles compounds. The control of the evolution of water and solutes content, in concentration process, at low pressure, is hard and inaccurate; in fact, small variations in pressure produce big changes in treatment. That is why the development of a new control system of water content during evaporation, allows an improvement in the quality of the final product without affecting the sensory aspects of the juice and would significantly improve the energy saving system installation. A novel technique used in the measurement and control of water content in biological systems is the dielectric spectroscopy in the microwave spectrum. The present research tries to design a methodology based in dielectric spectroscopy, in the range of microwaves, to quantify the content of water and solute content and to describe the relation between them, in orange juice during the evaporation by heating at low pressure. The work was conducted according to assess about 45º Brix concentration of orange juice by using at least 55ºC temperature and low pressure. Low pressure is created by using a chamber of pressure and allow us to have 40-45 Mbar. The low pressure also lets the use of low temperature that does not prejudice the quality of the orange juice. The soluble content changes with the development of the concentration and it is measured with the refract meter and correlated with microwave spectra. Results show a correlation between the loss factor at relaxation frequency with the water and solute content, in two different ranges of concentration, showing two water-solute relations, with different physical properties.