Integrated membrane process for blackcurrant (Ribes nigrum L.) juice concentration

The concentration of pretreated blackcurrant (Ribes nigrum L.) juice by reverse osmosis (RO) membrane was investigated in this study. The pretreatment steps were crushing, enzyme dosage, pressing and then clarification of the raw juice by ultrafiltration (UF). Polyethersulphone, tubular UF membrane on low pressure and temperature (4 bar, 25 degrees C) was used for this last pretreatment step. RO process was studied on a laboratory plant unit with flatsheet membranes to preconcentrate the clarified blackcurrant juice. The RO experiments were carried out on different transmembrane pressures (30-50 bar) and on low temperature (30 degrees C) for a mild concentration of the juice. At higher pressure the permeate flux was higher and the tithe of concentration decreased. The initial total soluble solid content of the juice was 8-10 degrees Brix, the concentrate of the RO was 22-25 degrees Brix. The quality of the RO product was evaluated: the antioxidant capacity, monomeric anthocyanin content, total acid content and total phenol content were determined in the samples. Mathematical modelling of the RO process was used to calculate the permeability coefficient. The RO can be applied as the first step of concentration, because it retains all the examined compounds over 99%, and it is an economic procedure. For further concentration membrane distillation or osmotic distillation can be proposed.