Novel biotransformation of betulin to produce betulone by Rhodotorula mucilaginosa

In this study, betulin was biotransformed to betulone by a strain of yeast. A primary screening was carried out using 47 microbial strains isolated from soil, that was able to grow in the presence of betulin as sole carbon source. The strain of yeast was identified as Rhodotorula mucilaginosa by Bruker MALDI Biotyper and 26S rDNA analysis. Under the optimum conditions, this yeast converted 52.65% of the added 4 mg/ml betulin to two products. One was betulone detected by high performance liquid chromatography (HPLC), isolated by preparative HPLC and characterized by high resolution mass spectrum (HRMS), 13C NMR and 1H NMR spectra. The other was a semi-volatile aromatic compound identified as 11,14-Octadecadienoic acid methyl ester by GC–MS. In the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging system, the activity of betulone was about 2 times higher than that of betulin.

► R. mucilaginosa could transform betulin to betulone.
► The biotransformation was optimized and 52.65% betulin was converted.
► Betulone was proved to have higher potential antioxidant capacity.