The concentration of orange juice using reverse osmosis associated with ultrafiltration processes was studied in a pilot-scale plant in order to evaluate this technology as a parcial substitute for evaporation in orange juice concentration. Assays were carrried out using 100 L orange juice containing 1.5% pulp (CTM Citrus). As a first step, the material was passed through the ultrafiltration unit to separate the pulp, pectic enzymes and microrganisms contained in the retentate. Polysulphone Romicom membrane (HF- 43), tubular modulus, with a 50,000 dalton cut molecular weight was employed, under 1.2 bar working pressure, yielding a concentration factor of 27.6. The retentate was pasteurised at 90°C in a specially designed scraped surface heat exchanger. Reverse osmosis was carried out in a DDS equipment (model LAB 20), using the compound film DDS membrane HR-95PP, with plate and frame type modulus. Tests were conducted under three pressure conditions, i.e., 20, 40 and 60 bar and results obtained after three repetitions for each condition. The pasteurised ultrafiltration retentate was added to the reverse osmosis retentate and then analysed for its chemical, microbiological, physical and sensory aspects. Reverse osmosis processes under 20, 40 and 50 bar have furnished concentration factors of 2.77, 3.53 and 3.59, containing soluble solids levels of 18.15, 23.44 and 29.80 % w/v, respectively. The permeate showed soluble solids contents of 3.3, 1.3 and 0.3 % w/v and acidity values of 262.50, 91.50 and 34.25 % w/v (as citric acid), under 20, 40 and 60 bar, respectively. Juices from all three treatments presented better defect and colour scores when compared with those regarding the original juice; juices obtained at 40 and 60 bar showed flavour scores close to optimum. The ratio, pH and formaldehyde values were similar under the three pressure conditions. In every case, concentrated as well as diluted juice samples were characterised as Newtonian fluids, showing increasing vicosities for corresponding increasing working pressures.
orange juice; reverse osmosis; concentration
