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Raw watermelon juice was concentrated in a laboratory-scale flat-plate ultrafiltration system incorporating polyethersulfone membranes with a molecular weight cutoff of 5 kDa. The experiments have been carried out over a wide range of transmembrane pressures (100-300 kPa). The effect of ultrafiltration with molecular weight cutoff of 5 kDa polyethersulfone membrane on concentrate properties is reported. The total soluble solid content of the permeate was found to be very good, while the ascorbic acid content was on the lower side as compared to feed. The analyses of flux decay according to fouling models reported in the literature revealed that the formation of a cake layer covering the entire surface of the membrane is the main cause of the membrane fouling.

The aim of this study is to evaluate the potential of tight ultrafiltration for the concentration of bioactive compounds in watermelon juice and also analyze the effectiveness of frozen storage for storing the juice concentrate. The concentration of the juice was performed at two different temperatures of 30 ± 2 C and 23 ± 2 C and at pressures of 2 and 3 bar for concentration factors of 1.5, 2, and 3. Total phenolic content in the concentrate was determined in terms of gallic acid and flavonoid concentration was analyzed in terms of rutin equivalent. Lycopene was determined spectrophotometrically using the hexane extraction method. The ultrafiltration (UF) process was successful in retaining a high percentage of bioactive compounds in the watermelon juice concentrate. Flavonoids showed the highest levels of concentration among the four important bioactive compounds. The ultrafiltration experimental set of T = 23 ± 2 C, P = 3 bar and volumetric concentration factor = 1.5 was found to be most feasible. Frozen storage at −18 C was successful in retaining a high percentage of bioactives in the concentrate after 1 month although vitamin C loss was on the higher side. Lycopene was highly preserved in the concentrate juice after frozen storage with retention of 93%.