Carotenoids as Antioxidants Samar Almohaimeed

Carotenoids are a class of more than 600 naturally occurring pigments synthesized by plants, algae, and photosynthetic bacteria. These richly colored molecules are the sources of the yellow, orange, and red colors of many plants.

International Agency for Research on Cancer. IARC Handbooks of Cancer Prevention: Carotenoids. Lyon: International Agency for Research on Cancer; 1998.

What is Carotenoids?

Jane Higdon. 2009.Carotenoids Alpha-Carotene, Beta-Carotene, Beta Cryptoxanthin, Lycopene, Lutein, and Zeaxanthin. Linus Pauling Institute

Fruits and vegetables provide most of the carotenoids in the human diet.

The most common dietary carotenoids are:

Alpha-carotenebeta-carotenebeta-cryptoxanthinLuteinLycopenezeaxanthin

Carotenoids family

the most prominent member of this group is b-carotene.

Carotenoids classified into two classes:

Carotenes: alpha-carotenebeta-carotenelycopene

Xanthophylls: beta-cryptoxanthinLuteinzeaxanthin

Carotenoids classes

Carotenoids Functions

Berg_et_al-2000. Journal_of_the_Science_of_Food_and_Agriculture

Diets high in carotenoid-rich fruits and vegetables are associated with reduced risk of: cardiovascular diseasesome cancersmany other chronic diseases

Why we do need Carotenoid?

Eat Orange, Red, or Yellow Food

http://www.everydayhealth.com/breast-cancer/1210/eat-orange-red-or-yellow-food-to-prevent-breast-cancer-3394.aspx

CHEMICAL PROPERTIES

With their extended system of conjugated double bonds the carotenoids contain a reactive electronic system which is susceptible to reactions with electrophilic compounds.

Such reactions are responsible for the instability of carotenoids towards oxidation.

In the presence of oxygen, carotenoids tend to autoxidise.The reaction of carotenoids with oxidising agents or free radicals depends on the length of the polyene chain and the nature of the end groups.

Carotenoid BioavailabilityAbsorption of carotenoids are influenced by many factors:

dietary lipidfiberpresence of vitaminsminerals

Carotenoids are highly hydrophobic it are easily dissolved in oil.

Fat in the diet has the potential to improve the absorption of carotenoids.

What is Antioxidants ?

Antioxidants protect cells against the effects of free radicals, which are potentially damaging compounds produced as by-products of metabolism, as well as through exposure to toxins and pollutants

Free radicals can cause cell damage that may contribute to the development of cardiovascular disease and cancers.

Carotenoids as Antioxidants

Carotenoids are one of the major groups of antioxidants found in fruits and vegetables.

The polyene chain is the structural feature that determines the chemical reactivity of carotenoids toward free radicals, then its antioxidant properties.

Ehab A. Abourashed. 2013. Bioavailability of Plant-Derived Antioxidants. Antioxidants 2013, 2(4), 309-325;

ANTIOXIDANT PROPERTIES

Carotenoids are highly lipophilicincorporated within cell membrane or associated with lipoproteins. Therefore, interaction of carotenoids with free radicals is greater.Therefore, antioxidant activity of carotenoids to scavenge free radicals is higher in a hydrophobic environment

(Tsuchihashi et al., 1995)(Clevidence and Bieri, 1993; Ribaya-Mercado et al., 1995a)

localization of carotenoids in the lipophilic component of the cell provides a greater resistance of lipid and lipoproteins to oxidative damage

Antioxidant StabilityPost-harvest changes in carotenoid levels depend on:the itemthe length of time of storagethe conditions (light, temperature, relative humidity)

During storage, spoilage occurs owing to a high relative humidity, which ultimately results in enzymatic degradation of the structure, allowing carotenoids to oxidise.

To extend carotene shelf-life:reducing the water content/activity or removing oxygen

Lycopene

Lycopene is a member of the carotenoid family, and it is the naturally occurring compound that gives the characteristic red color to the tomato, watermelon, pink grapefruit, and orange.

Biological Function of lycopene

The biological function of lycopene is determined by its structure.

Lycopene is a lineal acyclic isomer of β-carotene. It contains 11 conjugated double bonds in the center part of the molecule and 2 unconjugated double bonds at each end

Since lycopene doesn’t contain β-ionone ring structure at the end of the molecule, it cannot be converted to vitamin A.

Lycopene Antioxidant

Lycopene, α-carotene, and β-carotene were studied for their inhibitory effects on hydroperoxide formation during oxidation of methyl linoleate.

Lycopene displayed a higher antioxidant effect compared to α-carotene and β-carotene,which is in accordance with the results of increased reactivity of lycopene with singlet oxygen and free radicals.

lycopene oxidative degradation

Lycopene can be converted into peroxyl radicals capable of acting as pro-oxidants and of undergoing autoxidation themselves.

Oxygen is introduced into lycopene in two ways: (a) oxidation of a methyl or methylene group(b) addition to a carbon-carbon double bond.

Oxidative degradation can occur at either end of the C40-carbon skeleton.

ReferencesJane Higdon. 2009. Carotenoids Alpha-Carotene, Beta-Carotene, Beta Cryptoxanthin, Lycopene, Lutein, and Zeaxanthin. Linus Pauling Institute

Ehab A. Abourashed. 2013. Bioavailability of Plant-Derived Antioxidants. Antioxidants, 2(4), 309-325

Berg et al.2000. The potential for the improvement of carotenoid levels in foods and the likely systemic effects. Journal of the Science of Food and Agriculture. 80:880±912

Karrer, P. and Jucker, E. 1950. Carotenoids. Elsevier, New York. Kawaguchi, A., Yutani, C., and Yamamoto, A. 2003. Hypercholesterolemic valvulopathy: An aspect of malignant atherosclerosis. Ther. Apher., 7:439–443.

Tsuchihashi, H., Kigoshi, M., Iwatsuki, M., and Niki, E. 1995. Action of beta- carotene as an antioxidant against lipid peroxidation. Arch. Biochem. Biophys., 323:137–147.

Clevidence, B.A. and Bieri, J.G. 1993. Association of carotenoids with human plasma lipoproteins. Methods Enzymol., 214:33–46.

Ribaya-Mercado, I.D., Ordovas, I.M., and Russell, R.M. l995a. Effect of β-carotene supplementation on the concentrations and distributions of carotenoids, vitamin E, vitamin A, and cholesterol in plasma lipoprotein and nonlipoprotein fractions in healthy older women. J. Am. Coll. Nutr., 14:614– 620.

Anguelovea, T. and Warthesen, J. 2000. Degradation of lycopene, α-carotene, and β-carotene during lipid peroxidation. J. Food Sci., 65:71– 75.

Erdman, J.W., Poor, C.L., and Dietz, J.M. 1988. Factors affecting the bioavail- ability of vitamin A, carotenoids, and vitamin E. Food Technol., 10:214– 221.

Agarwal, S. and Rao, A.V. 2000b. Role of antioxidant lycopene in cancer and heart disease. J. Am. Coll. Nutr., 19:563–569.