Electrospray ionization mass spectrometric investigations of α-dicarbonyl compounds—Probing intermediates formed in the course of the nonenzymatic browning reaction of l-ascorbic acid

A new method is presented which allows the simultaneous detection of various α-dicarbonyl compounds generated in the course of the nonenzymatic browning reaction initiated by thermal treatment of l-ascorbic acid, namely: glyoxal, methylglyoxal, diacetyl, 3-deoxy-l-pentosone, and l-threosone. 3-Deoxy-l-threosone was successfully identified as a new C4-α-dicarbonyl structure for the first time in the degradation of Vitamin C by application of this non-chromatographic mass spectrometric approach. Moreover, a more detailed elucidation of the mechanistic scenario with respect to the oxidative and nonoxidative pathways is presented by using dehydro-l-ascorbic acid and 2,3-diketo-l-gulonic acid instead of l-ascorbic acid as a starting material. Furthermore, the postulated pathways are corroborated with the aid of 13C-isotopic labeling studies. The investigations were extended to baby food, and the successful detection of α-dicarbonyl compounds characteristic for Vitamin C degradation proved the matrix tolerance of the introduced method.