Abstract
Capsicum species produce fruits that synthesize and accumulate carotenoid pigments, which are responsible for the fruits’ yellow, orange and red colors. Chili peppers have been used as an experimental model for studying the biochemical and molecular aspects of carotenoid biosynthesis. Most reports refer to the characterization of carotenoids and content determination in chili pepper fruits from different species, cultivars, varieties or genotypes. The types and levels of carotenoids differ between different chili pepper fruits, and they are also influenced by environmental conditions. Yellow-orange colors of chili pepper fruits are mainly due to the accumulation of α- and β-carotene, zeaxanthin, lutein and β-cryptoxanthin. Carotenoids such as capsanthin, capsorubin and capsanthin-5,6-epoxide confer the red colors. Chromoplasts are the sites of carotenoid pigment synthesis and storage. According to the most accepted theory, the synthesis of carotenoids in chili peppers is controlled by three loci: c1, c2 and y. Several enzymes participating in carotenoid biosynthesis in chili pepper fruits have been isolated and characterized, and the corresponding gene sequences have been reported. However, there is currently limited information on the molecular mechanisms that regulate this biosynthetic pathway. Approaches to gain more knowledge of the regulation of carotenoid biosynthesis are discussed.
Highlights
Carotenoids are widely distributed in nature and are synthesized by all photosynthetic organisms as well as non-photosynthetic microorganisms, such as fungi and some bacteria [1]
The first step in plant carotenoid biosynthesis pathway is the formation of phytoene (Figure 2); this is a two-step condensation reaction with two geranylgeranyl pyrophosphate (GGPP) molecules catalyzed by phytoene synthase (PSY) [1]
These results demonstrated that chromoplasts are the site of carotenoid biosynthesis and that those carotenoids derived from β-carotene are predominantly synthesized during fruit ripening
Summary
Carotenoids are widely distributed in nature and are synthesized by all photosynthetic organisms (cyanobacteria, algae and plants) as well as non-photosynthetic microorganisms, such as fungi and some bacteria [1]. Carotenoids have an essential function in human nutrition and health; humans are unable to de novo synthesize vitamin A from endogenous isoprenoid precursors, but plant carotenoids (β-carotene, α-carotene, γ-carotene and β-cryptoxanthin; provide the primary dietary source of provitamin A (meaning they can be converted into retinol) [17] In addition to their nutritional value, carotenoids, acting as antioxidants, have been implicated in reducing the risk of cancer and cardiovascular diseases [18]. Carotenoids have a broad variety of applications, such as nutrient supplements, for pharmaceutical purposes, in animal feeds [12], coloring foods, cosmetics and nutraceutical agents as well [4]
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