Chemical, Physical, and Functional Properties of Cod Proteins Modified by a Nonenzymic Free-Radical-Generating System

Chelated ferric iron, hydrogen peroxide, and ascorbate were used to generate hydroxyl radical in washed, minced cod muscle. Protein carbonyl content increased between 2 and 24 h of storage at 5 °C on treatment with the free-radical-generating system (FRGS); it increased less if that storage period included a freeze/thaw process. There was an equal loss of sulfhydryl groups on treatment with the FRGS for 2 or 24 h with or without a freeze/thaw treatment. Electrophoretic results suggested disulfide formation. Treatment with the FRGS and a freeze/thaw process decreased protein solubility; a combination of the two was synergistic. Washed, minced cod muscle had improved gelation and emulsification characteristics when treated with the FRGS if the muscle tissue was not frozen but had poorer qualities if it was frozen. A model is proposed to explain the improvement of gelation and emulsification properties on exposure to the FRGS as well as its loss when exposed to a freeze/thaw process. Keywords: Proteins; free radical effects on; free radical effects on proteins; oxidation of proteins; cod proteins