Thermal and Photochemical Degradation of Carotenoids - Carotenoids: Physical, Chemical, and Biological Functions and Properties - page 229

12 Thermal and Photochemical

Degradation of Carotenoids

Claudio D. Borsarelli and Adriana Z. Mercadante

CONTENTS
12.1 Introduction .......................................................................................................................... 229
12.2 Thermally Induced Degradation .......................................................................................... 229
12.2.1 Thermal Degradation in Model Systems .................................................................. 231
12.2.2 Thermal Degradation in Food Systems .................................................................... 235
12.3 Direct and Sensitized Light-Induced Degradations.............................................................. 239
12.3.1 Photolysis in Model and Food Systems .................................................................... 239
12.3.2 Photosensitized Degradation in Model and Food Systems.......................................246
12.4 Conclusions........................................................................................................................... 249
Acknowledgments .......................................................................................................................... 250
References ...................................................................................................................................... 250

12.1 INTRODUCTION
The most characteristic feature of the carotenoid structure is the presence of several conjugated
double bonds in the chain. The polyene chain is responsible for the light absorption properties and
also for the susceptibility of carotenoids to degradation under high temperature, low pH, light, and
reactive oxygen species, among other factors. Nevertheless, heat processing has become an impor-
tant part of the food chain, and both processed and fresh foods are often exposed under l uorescent
light in supermarkets.
Although carotenoids are naturally stabilized by the plant matrix, cutting or disrupting of fruit
and vegetable tissues favors their exposure to oxygen and endogenous oxidative enzymes, thus pro-
voking their isomerization and oxidation. Differences between fruit and vegetable species, such as
the localization of carotenoids in the tissue and its physical state, may be crucial factors for the sus-
ceptibility of these pigments to trans to cis isomerization and oxidation reactions. In food systems,
the mechanisms involved in both thermal and photochemical degradations are much more complex
than in model systems. Along with the environmental factors and the carotenoid structure that
play important known roles, the physical state and location in cellular organelles, and interactions
between different naturally occurring food compounds are much more difi cu lt to pre d ict. T herefore,
comparison of published data regarding the extension of carotenoid degradation is a difi cult task
since different foods are processed and stored under different combinations of temperature, light
and time, etc. and such conditions are sometimes only partially described.

12.2 THERMALLY INDUCED DEGRADATION
Although trans to cis isomerization per se is not expected to cause major changes in color, it is
the i rst step for intramolecular cyclization to form cyclic volatile compounds under conditions
of high temperature. The oxidation of carotenoid is also required for subsequent reorganization

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