Thermal and free-radical-mediated transformation of selected phytochemicals

Carnosol, an antioxidant isolated from rosemary, was thermally decomposed at 180°C in a fat-like paraffin medium. Two known antioxidative quinones were isolated and identified as decomposition products. They are miltirone and dehydrorosmariquinone. The conversion of carnosol to miltirone and dehydrorosmariquinone may explain the observed antioxidant activity of rosemary extract in products such as potato chips.; The radical-scavenging mechanism of carnosol was studied by reacting with 2,2-diphenyl-1-picryhydrazyl (DPPH), which is a stable free radical. The reaction product was isolated, and identified as a quinone compound. The two hydroxy groups on B-ring of carnosol were converted into an ortho-quinone structure. It suggested that a carnosol molecule could scavenge two radicals.; The Maillard reaction of selenomethionine and glucose was studied. In order to gain a better understanding of the formation of organoselenium in food system. The effects of time of heating and of pH on the volatile compounds formed in a selenomethionine-glucose were investigated by a model system. The study also monitored the interaction between organoselenium and sulfur compound in the Maillard reaction. The organoselenium and mixed organoselenium-sulfur compound generated were identified by EI/MS and NH₃-CI/MS. Pyrazines and dimethyldiselenide are major flavor compounds generated from the glucose and selenomethionine model system. In pH9 solution, 6 selenium-containing compounds are identified, including CH₃-Se-H, CH₃-Se-O-CH ₂-CH₃, CH₃-Se-CH₂-CH₂-CH ₃, dimethyl diselenium, ethyl selenoacetate, vinyl selenoacetate, and selenotrithiolane. In pH3 solution, the selenium-containing compounds identified are dimethyl diselenide, CH₃-Se-CH₂-CO-CH₃, ethyl selenoacetate, vinyl selenoacetate, Me-Se-O-Se-Me, selenotrithiolane, and one unknown compound. The formation of pyrazine and dimethyldiselenide is favored by higher pH. In unbuffered system, a pH change of 3 or more pH units may occur, and this may affect the formation of Maillard reaction products dramatically. Sulfur can easily interact with selenium-containing compounds, but does not affect the formation of pyrazines. The major organoselenium-sulfur compounds identified are CH₃-Se-SH, diallylsulfide, allyl methyl selenide (MeSeAll), dimethyldiselenide, CH₃-Se-CH₂-COOH, CH₃-Se-S-CH₂-CH=CH₂, CH₃-Se-Se-S-CH ₃, CH₃-Se-S-CH₂-COOH, CH₂=CH-CH ₂-S-S-Se-H, CH₃-Se-S-S-CH₂-CH=CH₂, and CH₃-Se-S-S-S-CH₂-CH=CH₂.