Processes for producing coenzyme Q10

A process for producing the reduced coenzyme Q10 represented by the following formula (I):

• which comprises culturing reduced coenzyme Q10-producing microorganisms in a culture medium containing a carbon source, a nitrogen source, a phosphorus source and a micronutrient to obtain microbial cells containing reduced coenzyme Q10 at a ratio of not less than 70 mole % among the entire coenzymes Q10, and extracting the reduced coenzyme Q10 by an organic solvent under the condition that the reduced coenzyme Q10 is protected from an oxidation reaction, to thereby obtain an extract containing not less than 70 mole % reduced coenzyme Q10 among the entire coenzymes Q10, and
• wherein the condition that the reduced coenzyme Q10 is protected from an oxidation reaction is selected from the group consisting of an atmosphere of inert gas, a high salt concentration condition where inorganic salts are contained in not less than about 5% in an aqueous phase, the condition in the presence of not less than 0.1 mole % of a strong acid with a pKa value of not more than 2.5 relative to 1 mole of reduced coenzyme Q10, the condition in the presence of ascorbic acid, citric acid or salts and esters thereof, and the condition in the presence of dithionous acid.