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, gelatin e and stripped rapeseed oil was established by freeze-drying. The glassy fo od model had a glass transition temperature of 61 +/- 2 degrees C determine d by Differential Scanning Calorimetry, and encapsulated oil as confirmed b y Optical and Scanning Electron Microscopy. Radicals were generated thermal ly with either the hydrophilic radical generator 2,2'-azobis(2-amidinopropa ne)dihydrochloride, or with the lipophilic radical generator 2,2'-azobis(2, 4-dimethyl-pentanenitrile), as confirmed by Electron Spin Resonance spectro scopy. Early events in lipid oxidation were monitored by analyses of conjug ated dienes and peroxides during dry storage at 25 degrees C for up to 7 we eks. Formation of lipid peroxides followed 0th order kinetics. The oxidatio n of the encapsulated oil was enhanced by radicals generated in the oil, an d oxygen was able to diffuse through the glassy matrix in a rate determinin g process. The hydrophilic radicals were found not to enhance oxidation and were concluded to be immobilized in the glassy matrix. (C) 1999 Elsevier S cience Ltd. All rights reserved.