Fate of polyphenols in forward osmosis

The forward osmosis (FO) is an emerging technique for high quality concentration of liquid foods. Polyphenols are natural compounds with important health function in fruit and vegetable juice. In this study, the impacts of membrane property, feed solution (FS) pH value, draw solution (DS) composition and concentration, and membrane fouling on rejections of 9 food polyphenols by FO were investigated. Polyphenol rejection was mainly dominated by size exclusion and electrostatic repulsion. Membrane with higher negative charge and selectivity exhibited higher rejection. The increased pH of FS could enhance negative charge of membrane and thus increased the rejection. Reverse solute diffusion of DS could also enhance rejection via hindering the forward diffusion of polyphenol. The pectin fouling layer acting as the additional filtration barrier could increase the rejection of most selected polyphenols. However, the rejection of polyphenols with smaller molecular size (less than 23.07 Å2) decreased with the pectin fouled membrane and this might be attributed to the effect of cake-enhanced concentration polarization. The present study revealed the fate of polyphenol in FO and provided vital information to further advance the FO application.