Improving β-glucosidase biocatalysis with deep eutectic solvents based on choline chloride

This work reports a group of new “green” reaction medium-deep eutectic solvents (DESs) as modes in the hydrolysis of p-nitrophenyl-β-glucopyranoside using β-glucosidase as a biocatalyst. The tested DESs consisted of mixtures of a choline salt and three different types of hydrogen bond donors: amides, alcohols and sugars. These eutectic solvents are easily accessible, biodegradable, and inexpensive alternatives to conventional ionic liquids. Herein, the DESs compared with 1-ethyl-3-methylimidazolium tetrafluoroborate and methanol were studied by evaluating enzyme activity and enzyme stability; and a novel DES, choline chloride: propylene glycol (ChCl:PG, 1:2) was believed to be the most appropriate solvent to improve the bioconversion efficiency. When ChCl:PG (40%, v/v) as a co-solvent, β-glucosidase activity was increased to 225% compared to buffer system. Moreover, the enzyme thermal stability in ChCl:PG retained 62% of their initial activity in the fifth day, which was superior to phosphate buffer solution and methanol. On the contrary, the enzyme was mostly deactivated in pure DESs, while adding a certain amount of water was able to eliminate the adverse effects. It can be concluded that the water content in the solvent system will significantly affect the activity of solvent on enzymes. The Kinetic analysis further described that an increase in enzyme affinity toward the substrate in the DESs system was responsible for the enhancement of enzymatic efficiency.