Carotenoid Derivates in Achiote ( Bixa orellana) Seeds: Synthesis and Health Promoting Properties

Abstract

Bixa orellana (family Bixaceae) is a neotropical fast growing perennial tree of great agro-industrial value because its seeds have a high carotenoid content, mainly bixin. It has been used since pre-colonial times as a culinary colorant and spice, and for healing purposes. It is currently used as a natural pigment in the food, in pharmaceutical, and cosmetic industries, and it is commercially known as annatto. Recently, several studies have addressed the biological and medical properties of this natural pigment, both as potential source of new drugs or because its ingestion as a condiment or diet supplement may protect against several diseases. The most documented properties are anti-oxidative; but its anti-cancer, hypoglucemic, antibiotic and anti-inflammatory properties are also being studied. Bixin's pathway elucidation and its regulation mechanisms are critical to improve the produce of this important carotenoid. Even though the bixin pathway has been established, the regulation of the genes involved in bixin production remains largely unknown. Our laboratory recently published B. orellana's transcriptome and we have identified most of its MEP (methyl-D-erythritol 4-phosphate) and carotenoid pathway genes. Annatto is a potential source of new drugs and can be a valuable nutraceutical supplement. However, its nutritional and healing properties require further study.

Keywords: achiote; annatto; anti-cancer; antigenotoxic; antioxidant; apocarotenoids; bixin biosynthesis; hypoglycemic.

FIGURE 1

(A) Bixa orellana L. buds, flower (left), fruit and seeds (right). (B) Carotenoid biosynthesis Pathway. Carotene biosynthesis start with the phytoene synthesis by condensation of two geranilygeranyl diphosphate molecules mediated by phytoene synthase enzymes (BoPSY1 and BoPSY2). The phytoene is convert to Lycopene by successive steps of desaturation (phytoene desaturase: BoPDS1 and BoPDS2; ζ-carotene desaturase: BoZDS) and isomerization (ζ-carotene isomerase: BoZ-ISO; Carotenoid isomerase: BoCRTISO1, BoCRTISO2 and BoCRTISO3). (C) Bixin biosynthesis pathway. Lycopene is convert into bixin by three serial step reactions. (1) Lycopene is cleaved at the 5-6 and 5′-6′ double bonds by carotenoid cleavage enzymes from family 4 (BoLCD; BoCCD4-1: KT359022; BoCCD4-2: KT359023; BoCCD4-3: KT359024). (2) Bixin aldehyde is the oxidation product of aldehyde groups by aldehyde dehydrogenase enzymes (BoBADH; BoALDH3I1: KT359036; BoALDH3H1: KT359033). (3) Norbixin is converted into bixin by the addition a methyl group in carboxyl groups by a methyl transferase enzyme belonging to SABATH methyl transferase family (BonBMT; BoSABATH3: KT359051; BoSABATH4: KT359052). Dashed lines indicate the position of lycopene cleavage. A single asterisk indicates the proved enzymes that convert lycopene into bixin. A double asterisk indicates the proposed new set of genes involved in bixin synthesis.