Concentrating Red Beet Juice Using Osmotic Distillation: Effects of Device Structure

Background and Objectives: Red beet juice, a potential source of valuable nutrients, is widely used as a colorant in food industries. In recent years, to avoid reduction of nutritional values of the red beet during concentration by thermal processing, an osmotic distillation (OD) technique has been suggested. Therefore, the major aim of the present study was to investigate effects of the flow rate, volume of feed and brine solutions and membrane active area on efficiency of the membrane concentration process of red beet juice. Materials and Methods: In this study, osmotic distillation process was used in a laboratory scale unit equipped with a hydrophobic polyvinylidene fluoride (PVDF) membrane with a pore size of 0.22 μm at 25˚C after centrifuging red beet juice at 4,000 rpm for 17 min. Furthermore, to investigate effects of feed and brine solution volumes on efficacy of the concentration process, two channel heights (2 cm and 2 mm in both feed and brine sections) were tested. Results: Based on the results, the high feed volume was more effective than the high brine volume for the increasing soluble solid content (SSC) of juice in a constant time. Moreover, it was found that if the process time included more than three hours, the membrane with a higher active area (131.75 cm2) significantly improved total soluble solid content of juice, compared to the membrane with a lower active area (87.83 and 43.91 cm2). Results showed that a higher volume and flow rate of both feed and brine included had the most desirable effects on concentration efficiency. Based on the findings, flux of the total soluble solid content rise can be considered as a practical parameter to study efficiency of the osmotic distillation. Conclusion: Efficiency of the concentration process of red beet juice using osmotic distillation can increase by the modification of module configuration and process setup.