Quantification of Radical Formation in Oil‐in‐water Food Emulsions by Electron Spin Resonance Spectroscopy

The tendency of formation of radicals in an oil‐in‐water food emulsion (a mayonnaise partly based on fish‐oil) was quantified by electron spin resonance (ESR) spectroscopy using the spin trapping technique. Among the spin traps examined, N‐tert‐butyl‐α‐phenylnitrone (PBN) was preferred for this type of product. Under mildly accelerated conditions (i.e. heating to 37C, a spin trap concentration of 2 mM ensured pseudo‐first order conditions for trapping of radicals in the assay for up to 36 h of thermal treatment. The resulting linearity between ESR‐signals and rate of radical formation allows a direct quantification by standardization against stable radicals dissolved in the product. The hydrophobic spin‐probe 12‐doxylstearic acid (in contrast to the hydrophilic 2,2,6,6‐tetramethyl‐l‐piperidinyl‐oxyl) gave a stable signal and a linearity existed between signal intensity and probe concentration.