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Chapter 6: Carotenoids

Pages 43-53
DOI: https://doi.org/10.1094/1891127004.006
ISBN: 1-891127-00-4


Topics Covered

  • Annatto
  • Saffron
  • Paprika
  • Tagetes
  • Lycopene
  • Miscellaneous Carotenoid Extracts
  • Synthetic Carotenoids
  • Health Aspects

Introduction to Chapter

The carotenoids are probably the best known of the food colorants and certainly are one of the largest groups of pigments produced in nature. They are very widespread; over 100,000,000 tons are produced annually in nature. Most of this amount is in the form of fucoxanthin in algae in the ocean and the three main carotenoids of green leaves: lutein, violaxanthin, and neoxanthin. Other pigments predominate in certain plants, such as lycopene in tomatoes, capsanthin and capsorubin in red peppers, and bixin in annatto. Colorant preparations have been made from all of these, and obviously the composition of the colorant extracts reflects the profile of the starting material. Bauernfeind (1) described many of the colorant preparations in detail.

Carotenoids can occur in nature in four states: 1) as crystals or amorphous solids in solution or associated with lipid media, 2) as esters of fatty acids (e.g., the lauric acid esters of capsanthin in peppers), 3) in combinations with sugars (e.g., the gentiobioside of crocetin), and 4) in combination with protein, where the carotenoid stabilizes the molecule (e.g., the combination of astaxanthin with protein forms the greenish-blue pigment in the shells of lobsters).

β-Carotene can be used as an example of the structure of carotenoids. It has β-ionone structures at each end of the molecule joined by a conjugated double bond system. The structure and numbering system for β-carotene are shown in Figure 6-1. The modifications on each ionone structure vary greatly—over 600 carotenoids are known to occur in nature. The color of the carotenoid pigment is a function of the number of conjugated double bonds in the molecule. For example, phytofluene (Fig. 6-2) has only five conjugated bonds and is colorless. Zeta-carotene has seven and is yellow. Neurosporene has nine and is orange. Lycopene (Fig. 6-1) has 11 and is red. All four of these pigments occur in tomatoes. Extension of the conjugation system into the ring structure does influence the color but not to the same extent as the open structure of lycopene; thus β-carotene with 11 double bonds is orange. Canthaxanthin (Fig. 6-2) also has 11 conjugated bonds extending into the ring structure, but the ring keto group shifts the visual color to the red. The symmetry of the canthaxanthin molecule also contributes to its stability.