Method for the simultaneous assay of diacetyl and acetoin in the presence of alpha-acetolactate: application in determining the kinetic parameters for the decomposition of alpha-acetolactate.

A simultaneous assay method for diacetyl and acetoin was developed to investigate the formation of diacetyl during the brewing of alcoholic beverages. A GC-MS analysis after the extraction from neutralized sample by ethyl acetate gave accurate assay results. The detection limit was below 0.1 mg/l and the assay was quantitative from 0.1 to 100 mg/l for both compounds. Unlike other methods, the assay results were unaffected by the presence of alpha-acetolactate (up to 26 mg/l), which easily decomposes to diacetyl or acetoin, because the extraction condition prevents the decomposition and extraction of this acidic compound. Since our assay is compatible with samples that contain alpha-acetolactate, the kinetic parameters for decomposition of alpha-acetolactate to diacetyl and acetoin were determined. The decomposition rate constants were affected by the ethanol concentration. Overall kinetics for the decomposition of alpha-acetolactate was formulated as a function of ethanol concentration, pH and temperature. The kinetics can be applied to alcoholic beverages such as sake.