EPR study of thermally generated free radicals in nuts

Abstract

EPR studies of free radicals generated in roasting process of peanut, almond, walnut and apricot are reported separately for the kernels and flakes. The raw flakes exhibit a weak singlet EPR signal, whereas raw kernels are EPR silent. Two different EPR signals are recorded in the course of roasting. One in flakes with g = 2.0040, which is independent of temperature and time of roasting and is attributed to C-centered free radical. The same C-centered (g = 2.0040) free radical is recorded at high temperature (>140°C) and for extended time (>20 min) of roasted kernels connected with burning of the material. However, an O-centered (g = 2.0048) free radical of 'lipid' type appears in kernels at roasting temperature of 100-140°C and short time (5-20 min). On the contrary, free radical concentration in kernels and flakes increases with increase in roasting temperature and decreases with the time after that. The kinetics of the decay of free radicals concentration in flakes and kernels is followed at room temperature under the storage environment (air or argon). © 2007 Institute of Food Science and Technology Trust Fund.