Bioconversion of yolk cholesterol by extracellular cholesterol oxidase from Brevibacterium sp.

An efficient process for reducing yolk cholesterol by enzymatic treatment was developed in this paper. Extracellular cholesterol oxidase (COD) from a mutant Brevibacterium sp. ODG-007, showed a strong capacity in bioconversion of yolk cholesterol to cholest-4-en-3-one, especially supplemented with NaCl and lipase C, as a yolk granule solubilizer. The bioconversion process was investigated first, to obtain basic information of the process and was further optimized by analysis of parameters, including COD concentration, dilution ratio and incubation time on the cholesterol conversion, employing Response Surface Methodology (RSM) and Central Composite Design (CCD). Under the optimum operational conditions: COD concentration of 5.39 U/g yolk powder, water: solid ratio of 3.54 and incubation time of 13.75 h, up to 85.6% yolk cholesterol was reduced, and the remaining cholestenone, an effective anti obesity medicine in the product, may raise its commercial value.