Hydroperoxide formation in rapeseed oil encapsulated in a glassy food model as influenced by hydrophilic and lipophilic radicals

A glassy food model based on emulsions of sucrose, maltodextrin 10, gelatine and stripped rapeseed oil was established by freeze-drying. The glassy food model had a glass transition temperature of 61±2°C determined by Differential Scanning Calorimetry, and encapsulated oil as confirmed by Optical and Scanning Electron Microscopy. Radicals were generated thermally with either the hydrophilic radical generator 2,2′-azobis(2-amidinopropane)dihydrochloride, or with the lipophilic radical generator 2,2′-azobis(2,4-dimethyl-pentanenitrile), as confirmed by Electron Spin Resonance spectroscopy. Early events in lipid oxidation were monitored by analyses of conjugated dienes and peroxides during dry storage at 25°C for up to 7 weeks. Formation of lipid peroxides followed 0th order kinetics. The oxidation of the encapsulated oil was enhanced by radicals generated in the oil, and oxygen was able to diffuse through the glassy matrix in a rate determining process. The hydrophilic radicals were found not to enhance oxidation and were concluded to be immobilized in the glassy matrix.