Concentration of ‘Oblachinska’ sour cherry juice using osmotic distillation

Osmotic distillation is a kind of mass transfer driven membrane process where the driving force is the vapour pressure difference between two solutions. Similar that membrane distillation (MD) in case of OD is also used hyrdophobic, porous, polymeric membranes. For the osmotic distillation process usually high concentration of osmotic agent, mostly salt solution (NaCl, CaCl2, K2HPO4, Kacetate) or some kind of organic solutions (polyethyleneglycol, glycerol, etc.) is used which can keep and sustain very low value of vapour pressure during the process. These osmotic agents able to perform the suitable vapour pressure difference with the high concentration and low vapour pressure value between the two solutions (Bailey et al., 2000, Cassano et al., 2007; Gostoli et al., 1999; Hongvaleerat et al., 2008). OD process based on a phenomenon: between two aqueous solutions, which have different water activities a volatile compound stream occurs to equalize the vapour pressure different of the two solutions. In case of OD, a microporous hydrophobic membrane is present between these solutions which separates them from each other because of its hydrophobicity and surface energy. Thus, aqueous solutions cannot penetrate into the pores but volatile compound molecules (water) evaporate from the higher water activity liquid-vapour interface (liquid food side) across the pores by diffusion and condense at the lower water activity vapour-liquid interface (osmotic agent side). Figure 1 shows the flow sheet of the osmotic distillation process (Bélafi-Bakó et al., 2007; Courel et al., 2000;Mansuori et al., 1999; Thanedgunbaworn et al., 2007.) Low operating temperature (ambient temperature) and atmospheric pressure can be facilitated to concentrate diluted aqueous solutions, which contain valuable heat-sensitive compounds. In case of fruit juice production, several reports have suggested the applications and possibilities of osmotic distillation to replace high energy demand evaporation. Although the implementation of such a technique at an industrial scale is not yet realized, a variety of fruit juice concentrations was performed experimentally by using OD and showed the potential of osmotic distillation. Cassano & Drioli (2007) examined concentration of kiwi juice. Thanedgunbaworn et al. (2007) clarified passion fruit juice. Rodriges et al. (2004) concentrated camu-camu juice and Hongvaleerat et al. (2008) concentrated pineapple juice using osmotic distillation. Experimental results showed that