Phytochemicals in Daucus carota and Their Health Benefits-Review Article

Abstract

Carrots are a multi-nutritional food source. They are an important root vegetable, rich in natural bioactive compounds, which are recognised for their nutraceutical effects and health benefits. This review summarises the occurrence, biosynthesis, factors affecting concentration, and health benefits of phytochemicals found in Daucus carota. Two hundred and fifty-five articles including original research papers, books, and book chapters were analysed, of which one hundred and thirty articles (most relevant to the topic) were selected for writing the review article. The four types of phytochemicals found in carrots, namely phenolics, carotenoids, polyacetylenes, and ascorbic acid, were summarised. These chemicals aid in the risk reduction of cancer and cardiovascular diseases due to their antioxidant, anti-inflammatory, plasma lipid modification, and anti-tumour properties. Numerous factors influence the amount and type of phytochemicals present in carrots. Genotype (colour differences) plays an important role; high contents of α and β-carotene are present in orange carrots, lutein in yellow carrots, lycopene in red carrots, anthocyanins in the root of purple carrots, and phenolic compounds abound in black carrots. Carotenoids range between 3.2 mg/kg and 170 mg/kg, while vitamin C varies from 21 mg/kg to 775 mg/kg between cultivars. Growth temperatures of carrots influence the level of the sugars, carotenoids, and volatile compounds, so that growing in cool conditions results in a higher yield and quality of carrots, while higher temperatures would increase terpene synthesis, resulting in carrots with a bitter taste. It is worthwhile to investigate the cultivation of different genotypes under various environmental conditions to increase levels of phytochemicals and enhance the nutritional value of carrot, along with the valorisation of carrot by-products.

Keywords: ascorbic acid; carotenoids; carrot; human health; phenolic compounds; polyacetylenes.

Figure 1

Carrot root anatomy: (A) longitudinal; (B) cross-section, showing the periderm, phloem, and xylem (www.carrotmuseum.co.uk).

Figure 2

Structures of phenolic acids: (A) p-hydroxybenzoic acid; (B) caffeic acid; (C) chlorogenic acid; and (D) the basic chemical structure of anthocyanins.

Figure 3

Schematic representation of the biosynthesis of chlorogenic acid via the shikimic acid pathway. Abbreviations: Aldol: aldol condensation reaction; ATP: adenosine triphosphate; EPSP: 5-enolpyruvylshikimate-3-phosphate synthase; NAD and NADH: nicotinamide adenine dinucleotide reductase and oxidase; NADPH: nicotinamide adenine dinucleotide phosphate-oxidase; PAL: phenylalanine ammonia lyase; TAL: tyrosine ammonia lyase; PLP: pyridoxal phosphate.

Figure 4

(A) Structures of carotenoids: (1) α-carotene; (2) β-carotene; (3) β-cryptoxanthin; (4) lutein; (5) lycopene; (6) zeaxanthin; (B) Structures of the polyacetylenes: (1) falcarinol; (2) falcarindiol; (3) falcarindiol-3-acetate.

Figure 5

Schematic biosynthetic pathway for carotenoids.

Figure 6

Schematic biosynthetic pathway for falcarinol type polyacetylenes.

Figure 7

Schematic representation of the biosynthetic pathway of ascorbic acid in carrot: (1) hexokinase; (2) phosphoglucose isomerase; (3) phosphomannose isomerase; (4) phosphomannose mutase; (5) guanosine diphosphate (GDP)-mannose pyrophosphorylase; (6) GDP-mannose epimerase; (7) GDP-l-galactose phosphorylase; (8) l-galactose-phosphatase; (9) l-galactose-dehydrogenase; (10) l-galactose-1,4-lactone dehydrogenase.