Ionic strength-response hyperbranched polyglycerol/polyacrylic acid hydrogel for the reversible immobilization of enzyme and the synthesis of biodiesel

Hyperbranched polyglycerol and acrylic acid were polymerized into smart hydrogel for enzyme immobilization. Lipase from Aspergillus oryzae was selected as model enzyme. Highest enzyme loading amount of 78.93 mg/g and relative enzyme activity of 67.02% were observed. The immobilized enzyme was further used for the synthesis of biodiesel, and the synthesis parameters were optimized with response surface methodology. The yield of fat acid methyl esters (FAMES) under the optimum synthesis condition was determined to be 95.98%. The immobilized enzyme showed good reusability for five consecutive operations without significant loss of FAMES yield. By means of regulating the ionic strength of aqueous solution, the immobilized enzyme was successfully released from the hydrogel. After the enzyme reload, FAMES yield of fresh immobilized enzyme still remained 90% approximately for five consecutive operations. The results demonstrated that the hyperbranched polyglycerol/polyacrylic acid hydrogels could be effectively applied to the enzyme carrier and biodiesel synthesis.