Microbial Transformation Of Curcumin Into Its Derivatives

Curcumin is a hydrophobic poly-phenolic compound,has a wide range of biological and pharmacological activities such as antioxidant,anti-inflammatory,antibiosis,anti-tumor,anti-HIV and so on.However,the clinical use of curcumin is limited to some extent by poor water solubility,short half-life and low bioavailability.Structural modification of curcumin has been proven to be a promising approach to resolve these problems.In this paper,a strain capable of transforming curcumin was selected by our group,the separation and purification of transformed products,the optimization of fermentation medium and biotransformation conditions were also investigated.Firstly,we found that curcumin could be efficient converted into two major derivatives of ? and ? by Rhodococcus sp.90-4.TLC analysis showed that product ? had a Rf value of 0.329 and product ?had a value of 0.505.HPLC analysis showed that the retention times of above two compounds were 26.4 min and 29.9 min,respectively.Subsequently,gel column chromatography and preparative thin layer chromatography were carried out for the separation and purification of transformed products by Rhodococcus sp.90-4.Through the methods we got 15.2 mg of product ? and 10.1 mg of product ? whose purity could reach above 95%.UV analysis showed that the maximum absorption wavelength of product ? and ? both were 280 nm.LC-MS analysis showed that the product ? had a molecular weight of 376 and 374 for product ?.According to the fragments ions information,product ? was tentatively identified as octahydrocurcumin and product? was hexahydrocurcumin.Then,the optimization of fermentation medium,in order to increase bacterial biomass and the yield of octahydrocurcumin,was carried out by single factor experiments.The obtained optimal medium was composed of(in g/L):glucose 40,yeast extract 20,Li2SO4 0.2,KH2PO4 1.5,K2HP04 1.5,MgSO4-7H20 0.6,NaCl 0.6.The biotransformation process was then optimized by investigating some key reaction parameters.The optimal conditions were as follows:pH 6.6,wet cells 300 g/L,curcumin concentration 100 mg/L,reaction for 36 h.Under above conditions,the biomass was 5.84 g/L(dry cell weight),and the yield of octahydrocurcumin was 59.89%,corresponding to a 2.98-fold increase compared with original medium.Finally,the optimization of fermentation medium,in order to increase bacterial biomass and the yield of hexahydrocurcumin,was also carried out by single factor experiments and orthogonal experiment.The obtained optimal fermentation medium was composed of(in g/L):peptone 35,glucose 20,(NH4)2SO4 1.0,K2HPO4 3.0,MgSO4·7H2O 0.6,NaCl 0.6.The biotransformation process was subsequently optimized by investigating some key reaction parameters.The optimal conditions were as follows:pH 6.6,wet cells 200 g/L,curcumin concentration 100 mg/L,reaction for 24 h.Under above conditions,the yield of hexahydrocurcumin was 74.48%,corresponding to a 1.63-fold increase compared with original medium.