Lutein: chemistry, biosynthesis, applications, and production biotechnology in plants

Among the xanthophylls, lutein is the second most important carotenoid in the world in terms of its application, ubiquity, and bioavailability. Being a yellowish-orange lipophilic water-insoluble crystalline solid, lutein is chemically recognised as (3R, 3′R, 6′R)-β, ε-carotene-3,3′-diol. It is a derivative of α-carotene, featuring two hydroxyl groups on its terminal rings. Naturally, lutein is biosynthesized through the mevalonate pathway, which occurs in the plastids of photosynthetic organisms. Lutein is dominantly found in petals of colorful flowers, egg yolks, and green leafy vegetables. Globally, marigold (Tagetes sp.) is the known source for commercial lutein extraction and production. Recently, microalgal protists have also garnered attention as lucrative alternatives to higher lutein production. Colloquially nicknamed the “eye vitamin” due to its unquestionable properties in preserving and improving eye health, lutein as a nutraceutical has many other industrial, pharmacological, and economic uses due to its antioxidative, antimicrobial, anti-inflammatory, antidiabetic, anticancerous, neuroprotective, cardioprotective, hepatoprotective, and wound healing properties. Apart from health-related applications, lutein also finds uses in food and dyeing industries as a nutritive food colorant and dye. Industrially, lutein is extracted through extraction techniques such as high-speed counter-current chromatography supercritical fluid extraction, enzyme-based extraction, and solvent-based extraction. Although, investigations have enabled the development of eco-friendly green wayouts of lutein production such as ultrasound-assisted extraction, microemulsion technique, microwave-assisted method, transgenics and omics approaches, and hydroponics along with response surface methodology to improvise the extraction process. Hence, the current review discusses the importance of lutein in terms of its chemistry, biosynthesis, applications, and production technologies in light of the above points.