Carbon coated monoliths as support material for a lactase from Aspergillus oryzae: Characterization and design of the carbon carriers

Tunable carbon-coated monoliths as carriers for enzyme adsorption are presented. Depending on enzyme properties and reaction conditions, the carrier can be adjusted to optimize enzyme loading. Carbon–ceramic composites were prepared by sucrose carbonization, polyfurfuryl alcohol (PFA) carbonization, and by growth of carbon nanofibers (CNFs) over deposited Ni. All carbons were treated in air and subsequently in 1 M HNO3, and analyzed with respect to porosity, morphology and surface chemistry. The composites were applied as a carrier for a lactase from Aspergillus oryzae. The CNFs proved to be the best carrier, with respect to enzyme loading. Untreated fibers could adsorb 115 mg lactase/g carbon. After air/HNO3 treatment this value increased to 360 mg/g. Porosity was not affected by air and air/HNO3 treatment, implying that lactase adsorption mainly depends on surface chemistry. A clear trend was observed between oxygen content of different CNFs and lactase adsorption. Ni could be removed completely from the fiber tips of CNFs by different concentrated acids—nitric acid, hydrochloric acid, and oxalic acid. However, with HCl and HNO3 the porosity and surface chemistry were affected. Treatment in oxalic acid removed Ni from the tips by complexation, without changing the porosity. For these samples, 30% of the Ni remained present in the sample as residual NiC2O4. This was confirmed by TGA-MS and XRD.