Raw Juice Concentration by Osmotic Membrane Distillation Process with Hydrophobic Polymeric Membranes

Hydrophobic polymeric membranes (PP, PTFE, and PVDF) were efficiently applied in juice concentration by osmotic membrane distillation process at room temperature. The properties of applied membranes were characterized by the value of static contact angle, hysteresis of contact angle, surface free energy, roughness, mean flow pore size, maximum pore size or bubble point, and the pore size distribution before and after their utilization in osmotic membrane distillation (OMD). Furthermore, the mechanical strength of the membranes was evaluated using the Mullen burst technique and characterization of fouling behavior was done. The impact of stripping solutions, characterized by different water activities (NaCl and CaCl2), type of membrane materials, and membrane morphology, on the transport properties in a dehydration process was evaluated. Apple and beet juices with a high level of antioxidants were chosen. The quality of juices has been assessed by determination of total polyphenols and antioxidant activity. In the dehydration process, the most efficient were 0.45-μm PTFE and 0.45-μm PVDF membranes (24 % improvement). No loss of polyphenol content or reduction of antioxidant activity was observed after the juice dehydration.