Abstract
Freeze concentration is an effective unit operation to concentrate liquid foods such as fruit juices without the use of high temperatures. Recently, the innovations of freeze concentration have been associated more with the one-step configurations than conventional freeze concentration systems (suspension crystallization), because of the simpler separation step. Assisted techniques that improve the process parameters of freeze concentration in one-step are important in achieving commercial viability. The vacuum (suction by a pump) is an interesting assisted technique applied to freeze concentration in a one step. The objective was to study the process parameters of vacuum-assisted freeze concentration applied to orange juice. As material raw, using orange var. Navel and the juice were filtered to separate solids that might interfere with the cryoconcentration process. We used a vacuum pump at 80 kPa as an assisted technique to force the separation of concentrate (solutes) from the frozen solution at controlled temperature condition (20 °C). Over the time, under vacuum condition, the solids content (expressed as °Brix) in the concentrated fraction increased significantly compared the original sample, showing a kinetic of the solute elution from the ice block. The results show an evident advantage using the vacuum as an assisted technique compared the atmospheric condition. In addition, the efficiency under vacuum achieved high values over 70%, with high values of ice purity. The freeze concentration process using vacuum is similar to the principle used by children to suck the sugar solution with attractive colorants from popsicles and takes advantage of the frozen matrix formed by veins (or channels) between the ice crystals containing the concentrated solution. Under these conditions, the frozen block (the ice) acts as a carcass through which the concentrated fraction (rich in solids) passes, collecting the concentrate by gravitation force. The vacuum-assisted freeze concentration is an effective technique to obtain an orange fruit juice concentrated using a system in a one step with advantages compared the conventional suspension crystallization, which needs several steps and an important equipment capital inversion.
