Autoxidation in the formation of volatiles from glucose-lysine

The formation of volatile compounds from an aqueous glucose-lysine model system heated in the presence of either a free radical initiator (pro-oxidant) or an antioxidant was investigated. alpha-Tocopherol, 2,6-di-tert-butyl-4-methylphenol (BHT), and rosemary extract were used as antioxidants, and alpha,alpha'-azobis(isobutyronitrile) (AIBN) was used as a free radical initiator. The experiments mere performed at pH 4 and 6, which were constantly maintained during the heating time by the addition of diluted NaOH. Principal component analysis was used to find similarities and differences among the model systems. Especially at pH 6 AIBN produces a depletion of pyrazine, 2-methylpyrazine, and 2,3-dimethylpyrazine, whereas the three antioxidants enhance the same compounds. This could be due to an autoxidation of the already formed pyrazines or of some intermediate: in particular, the sensitive material could be the Ct fragment necessary for the formation of pyrazine, 2-methylpyrazine, and 2,3-dimethylpyrazine, but not of 2,5-dimethylpyrazine.