Flavor Draw Solution on Apple Juice Concentration by Forward Osmosis Technology

The purpose of this experiment was to explore the application of forward osmosis (FO) technology in apple juice concentration. The reverse solute diffusion (RSF) acted as functional agents in the juice. Two organic acids (malic acid and citric acid) and two sugars (fructose and sucrose) were selected as draw solution (DS) to explore the effects of DS concentration, membrane orientation and membrane recycling on concentrated apple juice. Water flux, RSF, and quality indicators of concentrated apple juice (including soluble solids (TSS), chroma, pH, total phenol concentration, etc.) were measured to assess the performance of FO membranes and control RSF. The results demonstrated that all the four DS could concentrate apple juice effectively. Malic acid and fructose exhibited the best performance at high concentrations. The highest average water fluxes were 5.06±0.73 and 6.33±0.70 L/m²/h, respectively. Fructose had the lowest RSF at 3 mol/L, while citric acid had the highest water flux at 3 mol/L. In multiple membrane cycling experiments, FO membrane showed good stability. The water flux remained stable. The RSF of carbohydrate DS was relatively stable, while organic acid DS was slightly increased due to slight corrosion. The quality analysis of concentrated apple juice showed that TSS and total phenol concentration increased significantly. All indexes were in line with national food safety standards. In conclusion, using malic acid, citric acid, fructose and sucrose as functional DS in FO could concentrate apple juice effectively, simultaneously increasing the content of TSS and total phenol in apple juice. This indicates a promising application potential for this method.