Recovery of oligosaccharides from steamed soybean waste water in tofu processing by reverse osmosis and nanofiltration membranes

The recovery of soybean oligosaccharides from the steamed soybean waste water in tofu (soybean protein curd) processing was carried out by using reverse osmosis and nanofiltration membranes. The feed solution was prepared by isoelectric and ultrafiltration treatments. Concentrations of the total oligosaccharides of 10% (w/v) and 22% (w/v) were obtained by using the RO and NF membranes in a batch operation. The chemical oxygen demand of the feed solution was simultaneously reduced from 8400-8700 ppm to 27-160 ppm. The permeate flux was mathematically analyzed by the osmotic pressure model with concentration polarization, the simulated results agreeing well with the experimental ones.