Investigation of Free Radicals Generated on the Surface of Baked Rice Pudding Samples Using Electron Spin Resonance (ESR) Spectroscopy

Abstract

Electron Spin Resonance (ESR) spectroscopy provides a powerful tool for investigating paramagnetic species generated during thermal treatment of organic matter. In this study, ESR was employed to examine heat-induced free radicals on the surface of baked rice pudding, a heterogeneous organic system containing carbohydrates that undergo thermally driven chemical transformations. Systematic measurements were performed to analyze the evolution of ESR signal intensity, peak-to-peak line width, and g-value as functions of heating temperature and duration. The results demonstrate that radical formation becomes significant above 200 degrees C, reaches a maximum at 350 degrees C, and decreases at higher temperatures. The g-values shift toward the free-electron value (g = 2.0023) with increasing temperature, reflecting changes in the electronic environment of the radicals. Kinetic analysis of time-dependent spectra yielded an activation energy of 12.8 kJ/mol for radical formation, consistent with values reported in other foods. Moreover, the radicals exhibited remarkable stability under ambient conditions, indicating persistent paramagnetic centers in the burnt surface layer. These findings highlight the applicability of ESR spectroscopy for characterizing thermally generated free radicals in heterogeneous organic systems. The study not only provides quantitative insight into the radical formation mechanisms but also demonstrates the use of a widely available food material as a model system for exploring spin dynamics under thermal treatment.