Category Archives: Carotenoids

Human health and carotenoids

Benefits of carotenoids for human health

Carotenoids belong to the category of bioactive compounds taken up with diet, that is, molecules able to provide protection against many diseases such as cardiovascular diseases, cancer and macular degeneration. They are also important for the proper functioning of the immune system.
Among the mechanisms that seem to be at the basis of their human health-promoting effects have been reported (Olson, 1999, see References):

  • the capability to quench singlet oxygen (see above);
  • the scavenging of peroxyl radicals and reactive nitrogen species;
  • the modulation of carcinogen metabolism;
  • the inhibition of cell proliferation;
  • the enhancement of the immune response;
  • a filtering action of blue light;
  • the enhancement of cell differentiation;
  • stimulation of cell-to-cell communication

Carotenoids, antioxidant activity and human health

Human Health and Carotenoids
Fig. 1 – Free Radical

Carotenoids, with the adaptation of organisms to aerobic environment, and therefore to the presence of oxygen, have offered protection against oxidative damage from free radicals, particularly by singlet oxygen, a powerful oxidizing agent (see also below).
Carotenoids stabilize singlet oxygen acting both chemical and physical point of view:

  • chemical action involves the union between the two molecules;
  • in physical action, the radical transfers its excitation energy to the carotenoid. The result is a low energy free radical and an excited carotenoid; later, the energy acquired by the carotenoid is released as heat to the environment, and the molecule, that remains intact, is ready to carry out another cycle of stabilization of singlet oxygen, and so on.

The capability of carotenoids to quench singlet oxygen is due to the conjugated double-bond system present in the molecule, and the maximum protection is given by those molecules that have nine or more double bonds (moreover, the presence of oxygen in the molecule, as in xanthophylls, seems to have a role).
Carotenoids are involved not only in singlet oxygen quenching, but also in the scavenging of other reactive species both of oxygen, as peroxyl radicals (therefore contributing to the reduction of lipid peroxidation) and nitrogen. These reactive molecules are generated during the aerobic metabolism but also in the pathological processes.

Lycopene, xanthophylls and human health

Lycopene, a carotene, canthaxanthin and astaxanthin, two xanthophylls present in foods of animal origin, are better antioxidants than beta-carotene but also than zeaxanthin that, with lutein, is involved in prevention of age-related macular degeneration.
Lycopene, in addition to act on oxygen free radicals, acts as antioxidant also on the radicals of vitamin C and vitamin E, that are generated during the antioxidant processes in which these vitamins are involved, “repairing them”.
Finally, lycopene exerts its antioxidant action also indirectly, inducing the synthesis of enzymes involved in the protection against the action of oxygen free radicals and other electrophilic species; these enzymes are quinone reductase, glutathione S-transferase and superoxide dismutase (they are part of the enzymatic antioxidant system).

Vitamin A and human health

Human Health and Vitamin A
Fig. 2 – Provitamin A Activity

Vitamin A, whose deficiency affects annually more than 100 million children worldwide, causing more than a million deaths and half million cases of blindness, is a well-known carotenoid derivative with many biological actions, being essential for reproduction, growth, vision, immune function and general human health.
In the human diet, the major sources of vitamin A are the preformed vitamin, which is found in foods of animal origins (meat, milk, eggs, etc), and provitamin A carotenoids, present in fruits and vegetables. In economically deprived countries, fruits and vegetables are the main source of vitamin A being less expensive than food of animal origin.
Of the more than 750 different carotenoids identified in natural sources, only about 50 have provitamin A activity, and among these, beta-carotene (precisely, all-trans-beta-carotene isomer) is the main precursor of the vitamin A.
Among the other carotenoids precursors of vitamin A, alpha-carotene, gamma-carotene, beta-cryptoxanthin, alpha-cryptoxanthin, and beta-carotene-5,6-epoxide have about half the bioactivity of beta-carotene.
Spinach, carrots, pumpkins, sweet potatoes (yellow) are example of vegetables rich in beta-carotene and other provitamin A carotenoids.
Acyclic carotenes, such as lycopene (the main carotenoid in the human diet), and xanthophylls, except those mentioned above (beta-cryptoxanthin, alpha-cryptoxanthin, and beta-carotene-5,6-epoxide), cannot be converted to vitamin A.

References

de la Rosa L.A., Alvarez-Parrilla E., Gonzàlez-Aguilar G.A. Fruit and vegetable phytochemicals: chemistry, nutritional value, and stability. 1th Edition. Wiley J. & Sons, Inc., Publication, 2010

Johnson E.J. The role of carotenoids in human health. Nutr Clin Care 2002;5(2):56-65 [Abstract]

Olson, J.A. 1999. Carotenoids. p. 525-541. In: Shils M.E., Olson J.A., Shike M., Ross A.C. “Modern nutrition in health and disease” 9th ed., by Lippincott, Williams & Wilkins, 1999

Ross A.B., Thuy Vuong L., Ruckle J., Synal H.A., Schulze-König T., Wertz K., Rümbeli R., Liberman R.G., Skipper P.L., Tannenbaum S.R., Bourgeois A., Guy P.A., Enslen M., Nielsen I.L.F., Kochhar S., Richelle M., Fay L.B., and Williamson G. Lycopene bioavailability and metabolism in humans: an accelerator mass spectrometry study. Am J Clin Nutr 2011;93:1263-73 [Abstract]

 

Functions of carotenoids in plants and foods

Through the course of evolution, carotenoids, thank to their unique physical and chemical properties, have proven to be highly versatile molecules, being able to perform many functions in many different organisms, like plants.

Carotenoids in photosynthesis

Carotenoids, in the early stages of the emergence of single-celled photosynthetic organisms, are probably been used for light harvesting at wavelengths different from those covered by chlorophyll. Therefore carotenoids, acting as light absorbing accessory pigments, have allowed to expand the range of solar radiation absorbed and so utilized for photosynthesis, energy that is then transferred to chlorophyll itself.
The major carotenoids involved in light harvesting, that accumulate in green plant tissues, are beta-carotene, lutein, neoxanthin, and violaxanthin, that absorb light energy in the 400- to 500-nm range.
Moreover, they protect chlorophyll from photooxidation (in humans, they may contribute to the protection of photo-oxidative damage caused by UV rays, thus acting as a endogenous photo-protective agents).

Carotenoids and autumn leaf color

Carotenoids and Plants: Autumn Leaf Color
Fig. 1 – Carotenoids and Autumn Leaf Color

Leaf color of deciduous plants in different seasons, green, yellow, orange or red, is due to the presence in them of natural pigments.
In spring and summer, the predominant pigment present in the leaf is chlorophyll, and therefore the color is green.
During the fall, the color changes from green to yellow, orange or red, depending on the type of plant: this is a consequence of the change, both qualitative and quantitative, in the pigment content.
In fact, as a result of the decrease of the temperature and daylight hours, the production of chlorophyll is interrupted and that already present is demolished into colorless metabolites. In this way the predominant pigments become carotenoids (yellow-orange), molecules much more stable than the chlorophyll, which remain in the leaf coloring it (it do not seem to be synthesized de novo), and anthocyanins (red-purple), which, unlike carotenoids, are not present during the growing season, but are synthesized in autumn, just before leaf fall. Therefore, it can be concluded that the red-purple color assumed from the leaves of certain plants is not a side effect of leaf senescence but results from anthocyanins de-novo synthesis.
Depending on the prevalence of carotenoids or anthocyanins, leaf color changes from green to yellow/orange, as in Ginkgo biloba (yellow), or red-purple as in some maples.

And plants with non green leaves?
Their color is not due to the absence of chlorophyll but the presence of very high amounts of other pigments, typically carotenoids and anthocyanins, that “cover” the chlorophyll, determining the color of the leaf.

Some functions of apocarotenoids in plants and foods

These oxygenated carotenoids, containing fewer than 40 carbon atoms, have many functions in plants and animals and are also important for the aroma and flavor of foods.
Some of their main functions include the following.

  • Apocarotenoids have significant roles in the response signals involved in the development and in the response to the environment (for example abscisic acid).
  • They can act as visual or volatile signals to attract pollinators.
  • They are important in the defense mechanisms of plants.
  • They have a role in regulating plant architecture.
  • An apocarotenal, trans-beta-apo-8′-carotenal, found in citrus fruits and spinach, with a low provitamin A activity, is used in pharmaceuticals and cosmetics, and is also a food additive (E160e) legalized by the European Commission for human consumption.
  • Apocarotenoids make an important contribution to the nutritional quality and flavor of many types of foods such as fruits, wine and tea. Two natural apocarotenoids, crocetin and bixina, have economic importance as they are used as pigments and aroma in foods.
  • Finally, a broad range of apocarotenals derive from oxidative reactions that occur in food processing; these molecules are intermediates in the formation of smaller molecules, important for the color and flavor of the food.
References

Archetti, M., Döring T.F., Hagen S.B., Hughes N.M., Leather S.R., Lee D.W., Lev-Yadun S., Manetas Y., Ougham H.J. Unravelling the evolution of autumn colours: an interdisciplinary approach. Trends Ecol Evol 2009;24(3):166-73 [Abstract]

de la Rosa L.A., Alvarez-Parrilla E., Gonzàlez-Aguilar G.A. Fruit and vegetable phytochemicals: chemistry, nutritional value, and stability. 1th Edition. Wiley J. & Sons, Inc., Publication, 2010

Carotenoids: definition, structure and classification

Carotenoids: contents in brief

What are carotenoids?

Carotenoids
Fig. 1 – Carrots

Carotenoids are soluble-fat pigments found throughout nature.
Carotenoids were discovered during the 19th century.
In 1831 Wachen proposed the term “carotene” for a pigment crystallized from carrot roots.
Berzelius called the more polar yellow pigments extracted from autumn leaves “xanthophylls” (originally phylloxanthins), from Greek words xanthos, meaning yellow, and phyllon, meaning leaf.
Tswett separated many pigments and called them “carotenoids.”

They occur in the chromoplasts of plants and some other photosynthetic organisms such as algae and in some types of fungi and bacteria; they are also produced by some invertebrates (Aphids).
There are more than 750 different carotenoids ranging in color from red (such as lycopene), to orange (such as alpha-carotene, beta-carotene, and gamma-carotene) or yellow (such as lutein, alfa-cryptoxanthin or violaxanthin); more than 100 have been found in fruits and vegetables.
In some green plants and in their parts, generally the darker the green color, the higher the carotenoid content: for example, carotenoid content in pale green cabbage is less than 1% of that in dark green one.
Fruit carotenoids are very different, and those present in ripe fruits may be different from those present in unripe fruits.
They also occur extensively in microorganisms and animals.
In plants, microorganism and animals carotenoids have diverse and important functions and actions.

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Chemical structure of carotenoids

Carotenoids are a class of hydrocarbon compounds consisting of 40 carbon atoms (tetraterpenes), with a structure characterized by an extensive conjugated double-bond system that determines the color (it serves as a light-absorbing chromophore): as the number of conjugated double-bond increases, color changes from pale yellow, to orange, to red.
In nature, they exist primarily in the more stable all-trans isomeric configuration, even though small amounts of cis isomers do occur too (they can be produced from all-trans forms also during processing).
Traditionally, carotenoids have been given trivial names derived from the biological source from which they are extracted. However, a semisystematic scheme exists: it allows carotenoids to be named in a way that describes and defines their structure.

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Classification of carotenoids

Depending on the presence or absence of oxygen in the molecule, they can be divided into:

  • xanthophylls, which contain oxygen, such as:

Antheraxanthin
Astaxanthin (red)
Auroxanthin
Bixin, E160b
Canthaxanthin (red), E161g
Capsanthin, E160c
Capsorubin, E160c
beta-Carotene-5,6-epoxide
alfa-Cryptoxanthin (yellow)
beta-Cryptoxanthin (orange)
Crocetin
Lutein (yellow), E161b
Lutein-5,6-epoxide or taraxanthin
Luteoxanthin
Lycophyll
Lycoxanthin
Neoxanthin
Rubixanthin
Tunaxanthin
Violaxanthin (yellow)
Zeaxanthin (yellow-orange)
Zeinoxanthin

  • carotenes, which lack oxygen, as such:

alfa-Carotene (orange)
beta-Carotene (orange), E160a
delta-Carotene
gamma-Carotene (orange)
Lycopene (red), E160d
Neurosporene
Phytoene (colorless)
Phytofluene
alfa-Zeacarotene
beta-Zeacarotene
zeta-Carotene

Depending on chemical structure they can be divided into:

  • acyclic carotenes: formed by a linear carbon chain such as:

zeta-Carotene
Phytoene (colorless)
Lycopene (red), E160d
Neurosporene
Phytofluene

  • cyclic carotenes: containing one or two cyclic structures such as:

alfa-Carotene (orange)
beta-Carotene (orange), E160a
gamma-Carotene (orange)
delta-Carotene
alfa-Zeacarotene
beta-Zeacarotene

  • hydroxycarotenoids (or carotenols): containing at least an hydroxyl group (xanthophylls) such as:

alfa-Cryptoxanthin (yellow)
beta-Cryptoxanthin (orange)
Lutein (yellow), E161b
Lycofill
Lycoxanthin
Rubixanthin
Zeaxanthin (yellow-orange)
Zeinoxanthin

  • epoxycarotenoids: containing at least an epoxic group (xanthophylls) such as:

Antheraxanthin
Auroxanthin
beta-Carotene-5,6-epoxide
Lutein-5,6-epoxide
Luteoxanthin
Neoxanthin
Violaxanthin (yellow)

  • uncommon or species-specific carotenoids such as:

Bixin, E160b
Capsanthin, E160c
Capsorubin, E160c
Crocetin

Note: although green leaves contain unesterified hydroxycarotenoids, most carotenols in ripe fruits are esterified with fatty acids. However, those of some fruits, particularly those that remain green when ripe (example kiwi fruit) undergo no or limited esterification.

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Apocarotenoids

Apocarotenoids are a class of carotenoids containing less than 40 carbon atoms, very widespread in nature and with extremely different structures.
They derive from 40 carbon atom carotenoids by oxidative cleavage that can occurs through non-specific mechanisms, such as photo-oxidation, or through the action of specific enzymes (these enzymatic activities, identified in plants, animals and microorganisms, are collectively referred to as carotenoid cleavage dioxygenases).
Some of the most well-known

  • vitamin A
  • abscisic acid
  • bixin, E160b
  • crocetin
  • trans-β-apo-8′-carotenal, E160e

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References

Boileau A.C., Merchen N.R., Wasson K., Atkinson C.A. and Erdman Jr J.W. cis-Lycopene is more bioavailable than trans-lycopene in vitro and in vivo in lymph-cannulated ferrets. J Nutr 1999;129:1176-1181 [Abstract]

de la Rosa L.A., Alvarez-Parrilla E., Gonzàlez-Aguilar G.A. Fruit and vegetable phytochemicals: chemistry, nutritional value, and stability. 1th Edition. Wiley J. & Sons, Inc., Publication, 2010

Engelmann N.J., Clinton S.K., and Erdman Jr J.W. Nutritional aspects of phytoene and phytofluene,carotenoid precursors to lycopene. Adv Nutr 2011:2;51-61. doi:10.3945/​an.110.000075

Olempska-Beer Z. Lycopene (synthetic): chemical and technical assessment (CTA). Office of Food Additive Safety, Center for Food Safety and Applied Nutrition. U.S. Food and Drug Administration. College Park, Maryland, USA [PDF]

Periago M.J., Bravo S., García-Alonso F.J., and Rincón F. Detection of key factors affecting lycopene in vitro accessibility. J Agr Food Chem 2013;61(16):3859-3867. doi:10.1021/jf3052994

Ross A.B., Thuy Vuong L., Ruckle J., Synal H.A., Schulze-König T., Wertz K., Rümbeli R., Liberman R.G., Skipper P.L., Tannenbaum S.R., Bourgeois A., Guy P.A., Enslen M., Nielsen I.L.F., Kochhar S., Richelle M., Fay L.B., and Williamson G. Lycopene bioavailability and metabolism in humans: an accelerator mass spectrometry study. Am J Clin Nutr 2011;93:1263-73. doi:10.3945/ajcn.110.008375

Wang X-D. Lycopene metabolism and its biological significance. Am J Clin Nutr 2012:96;1214S-1222S. doi:10.3945/​ajcn.111.032359