The turbidity of sour orange juice after juice extraction affects on quality, shelf-life and concentration of juice. Therefore, juice clarification is an important operation in the fruit processing industry. The goal of this study was evaluating the effect of membrane operation parameters including pressure (120-220 kPa) and temperature (25-35 ºC) on the permeate flux and hydraulic resistance of sour orange juice during ultrafiltration clarification. Response surface methodology (RSM) was used to optimizing the operating parameters. Results of the experiments showed that the permeate flux was raised with increasing of temperature, but total hydraulic resistance (RT), concentration polarization resistance (Rcp) and gel layer resistance (Rg) was decreased in this condition. The permeate flux, membrane resistance (Rm), RT, Rcp and fouling index was raised with increasing in pressure. The Rm and fouling index are showed different behavior depending on temperatures level. Results of process optimization indicated that the best conditions to maximize of permeate flux, and to minimize of fouling index and RT achieved at 35 ºC and 120 kPa for a maximum desirability of 0.761.
