Effect of ultrafiltration process on rheology and color indices of sour orange juice

  Fruit Juice is beverage that consist of great nutritional value, rich in antioxidants and essential minerals for human health. Maintenance procedures for juices are consist of heat treatment, freezing, cooling and for some juices; clarification and filtration. Clarification is the separation of dispersed and colloid compounds from the system and the maintenance of compounds that are actually solved in the system. In chemical clarification methods (classic) different types of enzymes (pectinase, amylase, protease, etc.) and Auxiliary clarifiers such as gelatin, bentonite, silica gel or a combination of these used. Classic methods are expensive and time-consuming as well as it is difficult to exclusion of these materials. In recent years, membrane filtration has been proposed as a new processing method. The use of membrane filtration is a good way to solve the problems caused by turbidity. The use of membrane processes in the clarification process makes the product more stable qualitatively and, due to the sterile nature of the process, removing of microorganisms is better than conventional methods. In this study, the effect of membrane parameters including pressure (1.2-2.2 bar) and temperature (25-35 ºC) on the viscosity, density and color indices (L *, a *, b *, Total Color Difference, Chroma and Browning index) of sour orange during membrane clarification was investigated. UF membrane process used for clarification of sour orange juice. Physicochemical tests was performed according to Institute of Standard and Industrial Research of Iran (2685). Viscosity was measured Rotational Brookfield viscometer. Image processing method was used for tracing of color changes after the process. Response surface methodology with central composite design was employed to predict the impact of UF process variables (temperature and operating pressure) on rheology and color of sour orange. Data analysis and graph drawing was performed using Design-Expert 9.0.0.7 software. Results of the experiments showed that the Browning index, viscosity and density was raised by increasing of temperature, but L* and TCD was decreased in this condition. The Browning index, Chroma and viscosity was decreased by increasing of pressure, but L*, b* and TCD was increased in this condition. Effect of temperature and pressure on a* index is not significant. Linear and quadratic models were the best models to predict of (density, TCD) and (L *, b *, BI and Chroma), respectively. The use of membrane processes, the quality (color) beverages and fruit juices (like orange) is improve. The membrane filtration of sour orange juice without enzymatic pretreatment had a suitable performance in clarification of it.