Aspergillus oryzae, kojic acid produced

Several of the pyran-4-ones found in nature are acidic by virtue of carboxylic acid or hydroxyl groups. Chelidonic (346), meconic (347), comenic (348) and pyromeconic (349) acids and maltol (350) are of plant origin but kojic acid (351) is produced by microorganisms, for example Aspergillus oryzae. Several compounds of this type are used to enhance the flavor of foods. The pyran-4-ones are more basic than their isomeric pyran-2-ones and this results in the formation of more stable salts with acids such as perchloric acid. 

Hydroxypyran-4-ones are potent flavouring materials of which maltol (427), present in roasted malt, is particularly well known. Amongst other features, it imparts a newly baked odour to bread. Kojic acid (712) is produced in an aerobic process by a range of microorganisms, notably Aspergillus oryzae, from a variety of carbohydrate sources and is used as a source of maltol. 

Apart from chelidonic acid 12, which occurs in the roots of celendine (Chelidonium majus), a few other 4//-pyran-4-one derivates are of importance. Maltol 16 occurs in the bark of larch trees and is formed by the dry distillation of starch and cellulose. Meconic acid 17 occurs in opium. Kojic acid 18 is produced by many microorganisms and was first isolated from Aspergillus oryzae, a microorganism used in Japan in the production of sake. 

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