Concentration of marc extracts by membrane techniques

By-products obtained from red currant processing still contain large amounts of useful components, e.g. pectin. Pectin was extracted from red currant marc with water at a solid/liquid ratio of 1:10. To reduce the operating costs of further possessing, we concentrated the pectin solution by membrane separation, i.e. nanofiltration (NF) and reverse osmosis (RO).The objectives of our work were to study the effects of the operating pressure and cross-volume flow rate on the flux and on the membrane separation concentration ratio in order to establish the optimum operating conditions and to evaluate the contributions of the fouling, cake and membrane resistances to the overall resistance.Flat-sheet RO and a spiral-wound NF membrane were applied in the work.The conductivity, the color, the viscosity and the TSS of the permeate and the concentrate were followed during the measurements.Concentration by RO resulted in an increase of the TSS content to 4.28°Brix; for NF the corresponding level was 8.88°Brix. The membrane resistance and the fouling resistance were the determinant relative to the gel resistance.