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Polysaccharides of Dendrobium officinale (DOP) need to be dehydrated and concentrated after extraction for further application. They are usually concentrated by thermal evaporation which consumes great energy. However, high viscosity of DOP makes the concentration more difficult even using non-thermal membrane technologies such as nanofiltration (NF) or reverse osmosis (RO). In this study, effects of process conditions, such as membrane orientations, draw solutions and their concentrations, and flowrate on forward osmosis (FO) concentration of viscous DOP were studied. Active layer to feed solution mode, cross flowrate at 240 mL min −1 , and draw solution of 3 M NaCl have been found as the optimal conditions. Foulants on the membrane surface with loose structure could be easily cleaned and removed by hydraulic flushing. DOP concentrated by FO achieved almost 1.3 times at the same time compared with that in NF and RO. DOP could be further concentrated for 1.5 folds at longtime without significant decrease in water flux. In addition, slight reverse solutes in FO process could reduce the viscosity of high viscous DOP, which was good for concentration. Accordingly, FO is a potential technology for concentration of high viscous polysaccharides such as DOP.

This study is to evaluate the athermal forward osmosis (FO) concentration process of blueberry juice using food additives as a draw solution (DS). The effects of food additives, including citric acid, sodium benzoate, and potassium sorbate, on the concentration processes are studied, and their effects on the products and membranes are compared. Results show that all these three food additives can be alternative DSs in concentration, among which citric acid shows the best performance. The total anthocyanin content (TAC) of blueberry juice concentrated by citric acid, sodium benzoate, and potassium sorbate were 752.56 ± 29.04, 716.10 ± 30.80, and 735.31 ± 24.92 mg·L−1, respectively, increased by 25.5%, 17.8%, and 19.9%. Meanwhile, the total phenolic content (TPC) increased by 21.0%, 10.6%, and 16.6%, respectively. Citric acid, sodium benzoate, and potassium sorbate all might reverse into the concentrated juice in amounts of 3.083 ± 0.477, 1.497 ± 0.008, and 0.869 ± 0.003 g/kg, respectively. These reversed food additives can make the TPC and TAC in juice steadier during its concentration and storage. Accordingly, food additives can be an excellent choice for DSs in the FO concentration process of juices, not only improving the concentration efficiency but also increasing the stability of blueberry juice.

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