Effect of high-temperature degradative processes on ketocarotenoids present in paprika oleoresins

Carotenoid pigments in six commercial oleoresins, qualitatively uniform in pigment composition, were thermodegraded to determine the degradation kinet ics in the two (red and yellow) isochromic fractions, structurally differen tiated by the presence or absence of keto groups. The different rate of deg radation of total pigment indicates that the oily medium modulates the degr adation reaction differently, so that each oleoresin shows a different stab ility. However, in all the oleoresins, the red pigment fraction is degraded at a higher rate than the yellow. Arrhenius curves reveal an isokinetic te mperature (T-isok) distinguishing two zones in which the degradation proces s has a different effect on each fraction. At temperatures above Tisok, deg radation is preferentially toward the red fraction, while at lower temperat ures, it is toward the yellow fraction. An isokinetic point between the two pigment fractions means that the thermal conditions at which the stability of the system is to be determined must be stated, as such conditions produ ce a different effect on each fraction.