Process parameters optimization of sweet orange juice ohmic heat-assisted vacuum evaporation and assessment of concentrate quality

Using an ohmic heat-assisted vacuum evaporation (OHVE) system, the process of concentrating clarified sweet orange fruit juice was carried out, and it was compared to a rotary vacuum evaporation (VE) method. Aim of the study was to maximize the total soluble solids (TSS) content in concentrated sweet orange juice and compare the quality of concentrated juice using both methods. A laboratory-scale ohmic heat-assisted vacuum evaporation system, coupled with a condensing unit and data logger, was designed and fabricated to achieve the targeted objective. We were able to optimize the OHVE process parameters, including temperature (ranging from 50 to 70 °C), holding time (between 40 and 120 min), voltage gradient (from 9 to 15 V/cm), and vacuum pressure (ranging from 400 to 600 mmHg (gauge)), by utilizing the Box-Behnken design of the response surface methodology (RSM) to achieve the desired TSS for the concentrated sweet orange fruit juice. Sweet orange juice concentrate was made using the OHVE and VE processes under the OHVE method’s optimal processing conditions, and its quality characteristics, including pH, density, ascorbic acid (AA), non-enzymatic browning index (NEBI), titratable acidity (TA), viscosity, as well as chromatic properties (L*, a*, b*, ΔE, hue angle, and chroma), were assessed. Quality characteristics of OHVE sweet orange fruit juice concentrate, produced at the optimized process independent variables (voltage gradient of 14.5 V/cm and vacuum of 569 mmHg (gauge)) and at varying temperatures (50–70 °C) and process times (0–120 min), were as follows – pH: 4.4 to 4.0, density: 1007 to 1306 kg/m3, AA: 0.039 to 0.033 mg/100 mL, NEBI: 0.272 to 0.344 at OD420 nm, TA: 0.23% to 2.03%, viscosity: 4.5 to 6.5 cP, L*: 25.75 to 10.59, a*: 0.001 to 8.37, b*: 10.97 to 16.39, hue angle: 56.69º to 89.99º, and chroma: 11.06 to 15.23. The results indicated that combining ohmic heating with vacuum evaporation, when related to the regular rotary vacuum evaporation, resulted a better retention of juice quality.