Coenzyme Q is an essential component of organisms in wide distribution from microorganisms to mammals, and is known as a mitochondrial electron transfer system constituent in cells of living bodies. Coenzyme Q serves as a transport of the electron transfer system, operating through cycles of oxidation and reduction within the mitochondria, and reduced coenzyme Q possesses antioxidant activity. The major component of coenzyme Q in humans is coenzyme Q10, which is a coenzyme Q species having 10 repeating structures in its side chain, and the reduced form is usually present on the order of 40 to 90% in living bodies. The physiological activity of coenzyme Q involves the activation of energy production through mitochondrial activation, activation of cardiac function, stabilization of cell membranes, cell protection through antioxidant activity, and the like.
Oxidized coenzyme Q10 is used as a health food in the United States and Europe, and as a medication for congestive heart failure in Japan. In recent years, it has come to be used in Japan as a functional nutritive food.
On the other hand, since reduced coenzyme Q itself has strong antioxidant action, it is possible to effectively increase the antioxidant activity in blood by supplying sufficient quantities of reduced coenzyme Q to blood. Increasing the antioxidant activity in blood is thought to have a wide range of usefulness for many diseases from being aggravated supposedly by active oxygen species, for example, preventing vascular lesions during ischemia-reperfusion, preventing restenosis in arteriosclerosis, preventing vascular lesions following cerebral infarction, preventing arteriosclerosis, preventing complications of diabetes.
It is known that reduced coenzyme Q10 can be obtained, for example, by well-known conventional processes such as synthesis, fermentation, extraction from natural sources, and the like, and then concentrating the reduced coenzyme Q10 fraction of the effluent resulting from chromatography (Japanese Kokai Publication Hei-10-109933). In this case, as described in the above-cited publication, the chromatographic concentration may be carried out after reduction of oxidized coenzyme Q10 contained in the reduced coenzyme Q10 with a conventional reducing agent such as sodium borohydride or sodium dithionite (sodium hydrosulfite), or reduced coenzyme Q10 to may be prepared by reacting an existing highly pure grade of coenzyme Q10 with the reducing agent mentioned above.
Moreover, as a result of intensive research, the present inventors established processes for producing high-quality reduced coenzyme Q10, which were disclosed in patent applications (WO 03/06408; WO 03/06409; WO 03/06410; WO 03/06411; WO 03/06412; WO 03/08363; and WO 03/32967).
However, reduced coenzyme Q10 is readily oxidized to oxidized coenzyme Q10 by a molecular oxygen. This oxidation is directly related to the problem of product quality such as formation of a difficult-to-remove byproduct, oxidized coenzyme Q10, and immixture thereof into the product. In order to obtain high-purity reduced coenzyme Q10 crystals and in order to stably maintain the obtained reduced coenzyme Q10 crystals, it is important to suitably protect them from the above-mentioned oxidation.