Highly Efficient Enzymatic Conversion of Rutin to Isoquercitrin and <scp>l</scp>-Rhamnose Using Deep Eutectic Solvents
Deqing Wang, Pu Zheng, Pengcheng Chen, Dan Wu
Abstract
Deep eutectic solvents (DESs), considered to be “green media”, have recently been employed in multiple applications including biotransformations. Here, a DES was used in the production of isoquercitrin and l-rhamnose from rutin by enzymatic transformation with recombinant α-l-rhamnosidase from Aspergillus niger. A solution synthesized from choline chloride and urea (ChCl-U) performed best in the conversion of rutin among 24 kinds of DESs. When 130 g/L rutin was used as the substrate, the conversion rate was 100% and the productivity of l-rhamnose and isoquercitrin was 208.68 mM/h under optimized conditions in ChCl-U solution, which was 1.12 times higher than that in buffer (186.92 mM/h). The recycling of ChCl-U solution was also investigated by aqueous two-phase system extraction of l-rhamnose, and ChCl-U/K2HPO4 was screened as the suitable extraction solvent. When the ChCl-U content was 34%, the extraction efficiency of l-rhamnose was 79.06% with a purity and primary crystallization yield of 96.28 and 66.49%, respectively. After five cycles of ChCl-U solution, the average enzymatic conversion rate of recycling was 95.63% with an average purity of 94.22% of the isoquercitrin prepared. After 10 cycles of reuse, the residual conversion rate was 61.14%. The results indicate that the DES has obvious advantages in biocatalytic processes involving flavonoid conversion.