Continuous juice concentration by integrating forward osmosis with membrane distillation using potassium sorbate preservative as a draw solute

Abstract

A green and sustainable technique is desired for juice concentration to increase its shelf life and save the transportation cost. In this study, we investigated an integrated forward osmosis-membrane distillation (FO-MD) process for juice concentration and developed a food preservative potassium sorbate as a renewable draw solute. The upstream FO process was used to concentrate apple juice in ambient operation conditions for preserving juice nutrition and flavor. Potassium sorbate preservative was developed as draw solute to minimize the accumulation of a draw solute in the concentrated juice without interfering juice flavor, and the slow diffusion of potassium sorbate preservative across the FO membrane to the feed juice concentrate can also prevent the bacterial growth during the concentration process by taking advantage of reverse salt flux. The downstream MD process was used to recover potassium sorbate draw solutes from the FO effluent and maintain the constant draw solute concentration for achieving stable water flux of FO membranes. Thin-film composite (TFC) polyamide membranes and poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) electrospun nanofibrous membranes were fabricated and employed in the FO and MD processes, respectively. Results illustrate that the integrated FO–MD process presents a synergistic flux balancing behavior and achieves a constant water flux for both FO and MD membranes. The FO–MD process was able to continuously concentrate apple juice over long-term bench-scale operation. Importantly, the concentrated apple juice has almost no loss in nutrition and also has very low amount of potassium sorbate (0.45 g/L) far below the required maximum level in food industry (1.00 g/L). Our work provides a food preservative potassium sorbate draw solute facilitated FO-MD process for juice concentration, which may have practical application potentials in the food processing.