Improving the enzymatic hydrolysis of dilute acid pretreated wheat straw by metal ion blocking of non-productive cellulase adsorption on lignin

Abstract

Eleven salts were selected to screen the possible metal ions for blocking the non-productive adsorption of cellulase onto the lignin of dilute acid pretreated wheat straw. Mg2+ was screened finally as the promising candidate. The optimal concentration of MgCl2 was 1mM, but the beneficial action was also dependent on pH, hydrolysis time and cellulase loading. Significant improvement of glucan conversion (19.3%) was observed at low cellulase loading (5FPU/g solid). Addition of isolated lignins, tannic acid and lignin model compounds to pure cellulose hydrolysis demonstrated that phenolic hydroxyl group (Ph-OH) was the main active site blocked by Mg2+. The interaction between Mg2+ and Ph-OH of lignin monomeric moieties followed an order of p-hydroxyphenyl (H)>guaiacyl (G)>syringyl (S). Mg2+ blocking made the lignin surface less negatively charged, which might weaken the hydrogen bonding and electrostatically attractive interaction between lignin and cellulase enzymes.