Studies on the Photosensitized Degradation of Food Constituents Part I

Volatile Carbonyl Compounds Produced by Photosensitized Degradation of Amino Compounds

Abstract

As one of the fundamental experiments on the sunlight off-flavor of foods, photo-sensitized degradation of amino acids with riboflavine in the atmosphere of air, O₂, and N₂ under visible light was investigated. Amino acids were oxidatively deaminized and decarboxylated to the corresponding aldehydes. Methionine was the most photolabile and gave almost exclusively methional. Degradation of methionine depended on the concentration of riboflavine and O₂, and was maximum at pH 7. One molecule of riboflavine converted 42 molecules of methionine into methional by the irradiation with 500W visible light for an hour. Among amino acids, valine, leucine, isoleucine, phenylalanine, methionine, tryptophan, and cysteine produced strong special odors. It is suggested that these amino acids may be responsible for the sunlight off-flavors of foods.