Abstract
Carotenoids are a class of natural pigments familiar to all through the orange-red colours of popular foods like oranges, tomatoes and carrots and the yellow colour of many flowers. They have been studied for a number of years because of their diverse roles in photobiology, photochemistry and photo medicine. Carotenoids are also added as colorants to many manufactured foods, drinks, and animal feeds, either in the forms of natural extracts (e.g annatto, paprika or marigold extracts) or as pure compounds manufactured by chemical synthesis. Carotenoids are often described as provitamins A, as this particular vitamin is a product of carotenoid metabolism. The distribution of carotenoids among the different plant groups shows no obvious pattern. b-Carotene is the most abundant in leafy vegetables, though the colour is masked by its co-existence with chlorophyll, and this carotenoid has the highest vitamin A activity. Zeaxanthin, a-carotene and antheraxanthin are also present in small amounts. In the tomato, lycopene is the major carotenoid, while fruits contain varying proportions of cryptoxanthin, lutein and antheraxanthin. In this review paper the natural occurrence of carotenoids (with focus on certain natural extracts) is described along with its structure and physicochemical properties. The biosynthesis - industrial synthesis and absorption of carotenoids is also discussed. Finally, a brief overview of analysis and properties of commonly available natural carotenoid extracts (annato, paprika, xanthophylls, lycopene) are also reported.
Highlights
Natural occurrence of carotenoids Carotenoids are lipid secondary metabolites that play essential roles in plants and are relevant compounds from a nutritional standpoint. (Etoh et al, 2000; Grobush et al, 2000). They attract much attention due to their proposed antioxidant properties and as natural pigments abundant in many fruits and vegetables that constitute an important part of the human diet. (Edge et al, 1997; Meléndez-Martínez et al, 2014)
Decades of research on carotenoids has improved our understanding of the role of these ubiquitous pigments, which have emerged as important players exerting a protective role against diseases associated with aging, including cancer, cardiovascular disease, cataracts, and agerelated macular degeneration (Bowen et al, 2015; Bermudez et al, 2005; Pantavos et al, 2015)
They have been studied for a number of years because of their diverse roles in photobiology, photochemistry and photo medicine (Pryor et al 2000)
Summary
Natural occurrence of carotenoids Carotenoids are lipid secondary metabolites that play essential roles in plants and are relevant compounds from a nutritional standpoint. (Etoh et al, 2000; Grobush et al, 2000). The antioxidant activity of carotenoids is a direct consequence of the chemistry of their long polyene chain (Farombi & Burton 1999; Boileau et al, 1999): a highly reactive, electron–rich system of conjugated double bonds susceptible to attack by electrophilic reagents, and forming stabilized radicals (Mortensen & Skibsted, 1997; Bast et al, 1998; Kiokias et al, 2008b) This structural feature is mainly responsible for the chemical reactivity of carotenoids towards oxidizing agents and free radicals, and other factors such as oxygen pressure (Jorgensen and Skibsted, 1993) and synergistic effect with other natural compounds may determine their antioxidant action or even prooxidant character in certain model systems (Mordi et al; 1993; Kiokias & Gordon 2004, Krinsky 2001; Palozza, 1998). Further experimental evidence of the antioxidant potential of certain carotenoid extracts following their incorporation in olive oil and olive oil based oil-in-water emulsions along with aspects of analysis and identification of their carotenoid pigments, are discussed by Kiokias and Varzakas (2014)
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