Red beet juice was clarified with microfiltration and the effects of operating parameters on clarification efficiency were evaluated. The red beet juice was clarified at transmembrane pressures of 0.1, 0.5 and 1 bar at two different flow rates (4.4 and 6 mL/s). Different mechanisms of membrane fouling were evaluated during the clarification process. The results showed that the best efficiency of membrane processing was at high transmembrane pressure and feed flow rate. The most dominant fouling mechanism at the process under high transmembrane pressure was the standard blocking; however, at high flow rate, the cake resistance was the main mechanism. Evaluation of physicochemical properties of red beet juice showed that the microfiltration process decreased turbidity, as well as total phenolic contents, total soluble solid and juice color. Also, evaluation of nutritional value of red beet juice showed that the antioxidant value of the juice and betacyanin and betaxanthin contents reduced. PRACTICAL APPLICATIONSConcentrate of red beet extract can be used as a natural colorant in food industry. Large particles can be adhered on the walls of evaporators during concentration process and cause off flavor. Current study showed that microfiltration can remove large particles; hence, the above-mentioned problems reduced. Efficiency of membrane processing was limited by fouling mechanism. Experiments showed that the cake formation is the main fouling mechanism, so membrane washing at high velocity can be useful to repair membrane efficiency.

A B S T R A C T Background and Objectives:Red beet extract concentrate can be used as a natural colorant in food products; however, destructive effects of thermal methods to produce juice concentrate decrease nutritional value in the final product. Materials and Methods:In this study, red beet extract was concentrated using osmotic distillation method, and the best pretreatment was evaluated to increase the efficiency of the concentration process. Also changes in some physicochemical properties such as betacyanins and betaxanthins contents, total phenolic compounds and antioxidant activity of red beet juice were evaluated by both the membrane and thermal concentration methods. Results:The results showed that the best concentration efficiency was obtained after pretreatment of the fresh juice with centrifugation at 1699 G for 17 min. Evaluation of the effect of both the membrane and thermal concentration processes on the physicochemical properties of juice showed that the membrane method did not change betacyanin and betaxanthin contents, total phenolic compounds, and antioxidant activity of the red beet extract. However, these properties decreased with the thermal concentration method by 26, 15, 11 and 13%, respectively. Conclusions:According to the results, osmotic distillation can produce red beet concentrate with more nutritional value than the concentrate produced with thermal method.