Reverse osmosis and forward osmosis concentration of cranberry juice: processing effects on juice quality

Abstract

Reverse (RO) and forward osmosis (FO) are membrane processes that are alternatives to thermal evaporation, operating at room or lower temperature during concentration of liquid foods, using less energy and retaining heat-labile components. Pasteurized cranberry juice (5.5° Brix, pH 2.6) was concentrated by RO at 3.5 MPa and 25 °C to 17.8° Brix and further concentrated by FO at 25 °C to 52.3° Brix. Potassium citrate (2.35 mol L⁻¹) was used as FO draw solution. Samples were stored refrigerated at 4 °C for 6 months. Total soluble solids, pH, water activity, titratable acidity, citric and malic acids, CIE color, % polymeric color, total phenolics, flavonoids, monomeric anthocyanins, DPPH and ABTS antioxidant activities were measured on concentrated and/or reconstituted samples before and after processing and monthly for 6 months. Total plate and yeast and mold counts were evaluated before and after FO processing and after 1, 3, and 6 months on concentrated samples. Results showed that during RO, anthocyanins decreased by 4% while FO induced no significant changes (p > 0.05) in the physicochemical properties. During storage, color values in the RO + FO concentrate decreased significantly (p < 0.05), with a total color change (ΔE) of 10.4 ± 0.9 at the end of 6 months. Polymeric color increased 2-fold while anthocyanins and DPPH Trolox equivalents decreased by 57% and 23% respectively after 6 month storage. Total phenolics, flavonoids and ABTS antioxidant activity were retained after RO and FO and through storage time. Total plate count was <1.5 log CFU mL⁻¹ before and after FO processing and after storage. No yeast and molds were detected. These findings suggested that a combined RO + FO can produce high-quality cranberry juice concentrate that retains quality attributes and bioactive components but may need frozen storage for preservation of anthocyanins.