Does Plant Breeding for Antioxidant-Rich Foods Have an Impact on Human Health?

Abstract

Given the general beneficial effects of antioxidants-rich foods on human health and disease prevention, there is a continuous interest in plant secondary metabolites conferring attractive colors to fruits and grains and responsible, together with others, for nutraceutical properties. Cereals and Solanaceae are important components of the human diet, thus, they are the main targets for functional food development by exploitation of genetic resources and metabolic engineering. In this review, we focus on the impact of antioxidants-rich cereal and Solanaceae derived foods on human health by analyzing natural biodiversity and biotechnological strategies aiming at increasing the antioxidant level of grains and fruits, the impact of agronomic practices and food processing on antioxidant properties combined with a focus on the current state of pre-clinical and clinical studies. Despite the strong evidence in in vitro and animal studies supporting the beneficial effects of antioxidants-rich diets in preventing diseases, clinical studies are still not sufficient to prove the impact of antioxidant rich cereal and Solanaceae derived foods on human.

Keywords: Solanaceae; antioxidants; carotenoids; cereals; food diet; polyphenols; pre-clinical studies.

Figure 1

The flavonoid biosynthesis and its regulation in cereal and Solanaceae crops. Scheme of the pathway leading to the production of flavonoids and phenolic acids in monocots (a) and dicots (b). Phenylalanine is first deaminated by PAL to produce cinnamic acid, then converted by C4H into p-coumaric acid, which can enter the synthesis of hydroxycinnamic acids (i.e., chlorogenic acid and other phenolics) or it can be conjugated with coenzyme A to produce 4-coumaroyl-CoA by 4CL. CHS catalyses the condensation of p-coumaroyl-CoA with three molecules of malonyl-CoA to naringenin chalcone, then converted to the flavanone naringenin by CHI. Indeed, naringenin may be converted to flavones by FNSI/FNSII (e.g., maysin in maize), to the red phlobaphenes, derived from condensation of the 3-deoxy flavonoids apiferol and luteoforol (a) and to dihydroflavonols, such as dihydrokaempferol (DHK), which can then be used by F3′H to produce dihydroquercetin (DHQ) or by F3′5′H to form dihydromyricetin (DHM) (b). Dihydroflavonols are then converted to flavonols (e.g., kaempferol, quercetin, and myricetin) by FLS. Downstream, DFR reduces the dihydroflavonols to their respective colourless leucoanthocyanidins, which are then converted into the coloured anthocyanidins (e.g., cyanidin, pelargonidin, and delphinidin). The main enzymes catalyzing the reactions in the pathway are reported in violet. Regulatory proteins belonging to diverse classes of transcription factors are marked with coloured dots. Branches leading to different classes of flavonoids and anthocyanins are indicated with diverse colours; in B, thicker purple and red arrows highlight the branch leading to the most abundant derived anthocyanins. The name of the enzymes is detailed in the abbreviation list.

Figure 1

The flavonoid biosynthesis and its regulation in cereal and Solanaceae crops. Scheme of the pathway leading to the production of flavonoids and phenolic acids in monocots (a) and dicots (b). Phenylalanine is first deaminated by PAL to produce cinnamic acid, then converted by C4H into p-coumaric acid, which can enter the synthesis of hydroxycinnamic acids (i.e., chlorogenic acid and other phenolics) or it can be conjugated with coenzyme A to produce 4-coumaroyl-CoA by 4CL. CHS catalyses the condensation of p-coumaroyl-CoA with three molecules of malonyl-CoA to naringenin chalcone, then converted to the flavanone naringenin by CHI. Indeed, naringenin may be converted to flavones by FNSI/FNSII (e.g., maysin in maize), to the red phlobaphenes, derived from condensation of the 3-deoxy flavonoids apiferol and luteoforol (a) and to dihydroflavonols, such as dihydrokaempferol (DHK), which can then be used by F3′H to produce dihydroquercetin (DHQ) or by F3′5′H to form dihydromyricetin (DHM) (b). Dihydroflavonols are then converted to flavonols (e.g., kaempferol, quercetin, and myricetin) by FLS. Downstream, DFR reduces the dihydroflavonols to their respective colourless leucoanthocyanidins, which are then converted into the coloured anthocyanidins (e.g., cyanidin, pelargonidin, and delphinidin). The main enzymes catalyzing the reactions in the pathway are reported in violet. Regulatory proteins belonging to diverse classes of transcription factors are marked with coloured dots. Branches leading to different classes of flavonoids and anthocyanins are indicated with diverse colours; in B, thicker purple and red arrows highlight the branch leading to the most abundant derived anthocyanins. The name of the enzymes is detailed in the abbreviation list.

Figure 2

A simplified overview of carotenoid pathway in cereal and Solanaceae crops. The first step in carotenoid biosynthesis is the condensation of two GGPP molecules to form phytoene catalysed by PSY, which is the main rate-limiting step in solanaceous fruits and cereal grains. Further, the conversion of phytoene to lycopene via sequential desaturation and isomerization reactions is catalysed by a set of four enzymes (PDS, ZISO, ZDS, and CRTISO). Lycopene is at the branch point of carotenoid synthesis since it can be cyclized to ß-carotene or α-carotene by LCYB and LCYE. Downstream, the sequential hydroxylation and epoxidation of these carotenes leads to the production of diverse xanthophylls (e.g., lutein and zeaxanthin). Regulatory proteins belonging to diverse classes of transcription factors are marked with coloured dots. The name of the enzymes is detailed in the abbreviation list.