EPR Methods for Studying Free Radicals in Foods

Although some roles for free radicals in foods have been proposed, relatively little research to document suspected radicals has been undertaken. EPR is a highly specific and sensitive technique for direct detection of free radicals; application of EPR to foods can reveal important information about radical reactions that may be responsible for food qualities and deterioration. To excite interest and encourage more definitive studies of free radicals in foods, this paper will introduce EPR spectroscopy, covering basic considerations necessary to obtain, interpret, and quantitate EPR spectra. Topics covered include calibration of magnetic fields and microwave frequencies for accurate determination of splitting constants and g-values (radical identification factors), quantification of EPR signals, methods for eliminating interference of water, instrumental and environmental conditions that must be controlled to obtain accurate and reproducible EPR spectra, and some pitfalls to avoid. Three guidelines are offered that, if followed, will ensure that data obtained reflects the radicals and reactions being studied rather than secondary or artifact radicals, that the quantitation is accurate, and that the interpretations are sound.