Introduction

Carotenoids are also called tetraterpenoids which are yellow, orange, and red organic pigments that are produced by plants and algae, as well as several bacteria, and fungi. Carotenoids give the characteristic color to pumpkins, carrots, corn, tomatoes, canaries, flamingos, salmon, lobster, shrimp, and daffodils. Carotenoids can be produced from fats and other basic organic metabolic building blocks by all these organisms.

The only land dwelling arthropods known to produce carotenoids are aphids, and spider mites, which acquired the ability and genes from fungi.  It is also produced by endosymbiotic bacteria in whiteflies. Carotenoids from the diet are stored in the fatty tissues of animals and exclusively carnivorous animals obtain the compounds from animal fat. In the human diet, absorption of carotenoids is improved when consumed with fat in a meal and Cooking carotenoid-containing vegetables in oil increases carotenoid bioavailability.

Sources of carotenoids

Carotenoids are pigments in plants, algae, and photosynthetic bacteria. These pigments produce the bright yellow, red, and orange colors in plants, vegetables, and fruits. Carotenoids act as a type of antioxidant for humans. There are more than 600 different types of carotenoids. Some can be converted into vitamin A when released into the body. A few of the most common caroten.oids include: alpha carotene, beta carotene, beta cryptoxanthin, lutein, zeaxanthin and lycopene.

Carotenoids must be consumed through the diet. They are best absorbed through a source of fat. Foods rich in carotenoids include: yams, kale, spinach, watermelon, cantaloupe, bell peppers, tomatoes, carrots, mangoes and oranges. Carotenoids are fat-soluble compounds, meaning they are best absorbed with fat. Unlike some protein-rich foods and vegetables, cooking and chopping carotenoid-rich foods increase the strength of the nutrients when they enter the bloodstream.

Carotenoids are classified into two main groups: xanthophylls and carotenes. Both types of carotenoids have antioxidant properties. In addition, some carotenoids can be converted into vitamin A, an essential component for human health and growth. This provitamin-A carotenoids include alpha carotene, beta carotene, and beta cryptoxanthin. Non-provitamin-A carotenoids include lutein, zeaxanthin, and lycopene.

Antioxidant activity

In plants, carotenoids have the important antioxidant function of quenching (deactivating) singlet oxygen, an oxidant formed during photosynthesis. Test tube studies indicated that lycopene is one of the most effective quenchers of singlet oxygen among carotenoids. They also suggested that carotenoids could inhibit the oxidation of fats (i.e., lipid peroxidation) under certain conditions, but their actions in humans appear to be more complex. Although important for plants, the relevance of singlet oxygen quenching to human health is less clear.

Some evidence suggests that carotenoids and/or their metabolites may upregulate the expression of antioxidant and detoxifying enzymes via the activation of the nuclear factor E2-related factor 2 (Nrf2)-dependent pathway. Briefly, Nrf2 is a transcription factor that is bound to the protein Kelch-like ECH-associated protein 1 (Keap1) in the cytosol. Keap1 responds to oxidative stress signals by freeing Nrf2. Upon release, Nrf2 translocates to the nucleus and binds to the antioxidant response element (ARE) located in the promoter of genes coding for antioxidant/detoxifying enzymes and scavengers.

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