Nonthermal Concentration of Red Beetroot Juice by Reverse Osmosis and Forward Osmosis.

This work reports on the use of reverse osmosis (RO) and forward osmosis (FO) for the nonthermal concentration of red beetroot juice. Commercial thermally concentrated juice (TCJ) diluted to single strength and freshly extracted, not from concentrate juice (NFC) were processed by RO with a thin film composite membrane, at 2400 kPa transmembrane pressure and 22°C-23°C. FO concentration was conducted with a cellulose triacetate membrane, at 25°C, using potassium citrate as osmotic agent. Water flux declined over time in both RO and FO, with a more pronounced decay for RO, indicative of membrane fouling. RO concentration plateaued at 17.3 °Brix ± 0.4 °Brix for TCJ and at 12.3 °Brix for NFC, while FO reached concentrations of 50.9 °Brix ± 2.9 °Brix and 49.7 °Brix for TCJ and NFC, respectively. No significant changes (p > 0.05) in juice color and betalain content were observed for any of the membrane concentrated TCJ samples; small decreases in betacyanin content and color occurred after both RO and FO of NFC A combined RO-FO process maintained product quality but did not present benefits in terms of speed of concentration. Overall, this work indicates that FO is a promising nonthermal method for the concentration of beetroot juice, with significant advantages compared to both thermal concentration and RO.