Kinetic studies of degradation of saffron carotenoids encapsulated in amorphous polymer matrices

Kinetic studies on degradation of saffron water soluble carotenoids (mainly crocins) encapsulated in three different amorphous matrices (pullulan and two polyvinylpyrrolidone, PVP, samples differing in their molecular weight) were carried out at different water activity (a(w)) conditions (0.43, 0.53 , 0.64 and 0.75) in the dark at 35 degrees C. Degradation of the polar pigm ents was monitored by periodic measurements of the coloring strength. Among the polymeric matrices used as wall materials, which largely decreased the oxidation rates of crocetin glycosides, PVP 40 was the most effective carr ier under all storage conditions. In the vicinity of the glass transition t emperature (T-g) zone, where pullulan and PVP360 undergo slate transformati ons, there was a change in the reaction rate. The lower degradation rates w ere observed for PVP40 under conditions where this matrix was fully plastic ized (i.e. rubbery) and "collapsed", implying that the degradation kinetics are not governed by factors related to the physical state and molecular mo bility of the inert matrix. Carotenoid losses have been observed even at te mperatures below the T-g of the polymeric matrices. (C) 2000 Elsevier Scien ce Ltd. All rights reserved.