Enhanced ultrafiltration flux rates by enzymatic hydrolysis in protein recovery from wheat starch effluent

Abstract

Wheat starch effluent contains several polysaccharide species which contribute to the formation of a viscous gel layer in the ultrafiltration of wheat starch effluent. Viscosity reduction tests with various hydrolytic enzymes on a wheat starch effluent concentrate revealed a commercial pentosanase, “Brew-N-Zyme Pentosanase” (Naarden), which was very effective at low doses (0.05 wt.% dry solids basis), was thermally stable at the ultrafiltration temperature of 70°C and had no proteolytic activity. Enzymatic hydrolysis considerably increased the permeate flux rate and the maximum achievable concentration in the ultrafiltration of wheat starch effluent from 9 to 18 wt.% solids. Flux-concentration profiles for wheat starch effluent and enzymatically hydrolyzed wheat starch effluent were closely fitted by modified mass transfer and pressure-driven models. The main resistance to permeate flux at the initial wheat starch effluent concentration was caused by adsorption of macromolecules on the surface of the membrane. This accounted for 57% of the total resistance for wheat starch effluent and 78% for enzymatically hydrolyzed wheat starch effluent. Enzymatic hydrolysis reduced the viscosity of the gel layer which was thus more easily removed by shear stress. Reduction of the thickness of the polysaccharide gel layer exposed the membrane to greater adsorption of macromolecules. At the final ultrafiltration concentration the reverse situation applied. The gel layer formed the most significant resistance accounting for 93% of the total resistance for wheat starch effluent and 80% for enzymatically hydrolyzed wheat starch effluent. In both systems, wall shear stress performed the important function of removing the mass flux of macromolecular material which impacted onto the surface of the gel layer.