The feasibility of polyacrylic acid (PAA)-coated magnetic nano-adsorbent for the recovery of Candida rugosa lipase from aqueous solutions was studied. The adsorption percentage was strongly dependent on the solution pH. With decreasing pH, the adsorption percentage increased rapidly from 20 to 90% at pH 7-5.5 and 98% adsorption could be achieved at pH 4.5-3.5. The adsorption behavior followed the Langmuir isotherm with a maximum adsorption amount of 0.605 mg mg-1 and a Langmuir adsorption equilibrium constant of 14.5 mL mg-1 in 0.03 M phosphate buffer at pH 3.5 and 25 °C. The adsorbed lipase could desorb in 0.03 M phosphate buffer at pH 9, and no significant activity loss was observed after adsorption/desorption. From the investigations on the pH effect, desorption, and activity assay, it was suggested that the lipase used might contain 20% inactive form. In addition, the electrostatic interaction between lipase and PAA was not significantly affected by the temperature at 15-35 °C, and both the adsorption and desorption of lipase were quite fast due to the absence of internal diffusion resistance. The whole result demonstrated that the PAA-coated magnetic nano-adsorbent was useful for the efficient and fast recovery of lipase, and might be used to purify the lipase by removing the inactive form at pH 9.
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