Production of high quality clarified pomegranate juice concentrate by membrane processes

• OD and CO were very efficient in preventing the quality of the clarified PJ.
• The CO was found to be very challenging to improve transmembrane flux.
• The CO was the most promising approach to achieve high quality PJ concentrate.
• TE resulted considerable losses in color and TAA, and in a marked formation of HMF.
• Pre-flocculation step improved the efficiency of the overall membrane-based system.

The potential of osmotic distillation (OD) and coupled operation of membrane distillation (MD) and OD processes (CO) for concentration of pomegranate juice was investigated comparatively with a view to the impact on product quality and process performance. The pomegranate juice (17° Bx) which was previously clarified by combined application of fining agents (gelatin and bentonite) and ultrafiltration (UF), was concentrated up to 55–57° Bx by OD, CO or thermal evaporation (TE). Both membrane-based concentration techniques were very efficient in preventing the original characteristics (pH, total titratable acidity (TTA), color characteristics, total antioxidant activity (TAA), total phenolic content (TPC), total monomeric anthocyanins (TMA), individual phenolics and organic acid composition) of the clarified juice. Concentration with TE, however, resulted considerable losses in natural color and TAA, and in a marked formation of hydroxymethyl furfural (HMF). CO was the most feasible approach for concentration of pomegranate juice, allowing to reach higher concentration levels in shorter periods of operation time with a slight increase (5 °C) in temperature of the juice in comparison with OD. The results of this study highlighted the need for an effective pre-clarification step prior to UF to contribute to the improvement of the efficiency of the overall membrane-based system.