**3. Chemistry of wheat polyphenols**

Among these cereals, wheat (*T*. *aestivum* L.) is a significant source of minerals, proteins, water-soluble vitamins, and dietary fibers. The wheat grain is divided into three parts such as endosperm (80–85%), bran (13–17%), and germ (2–3%) and comprises all essential nutrients. Generally, wheat grain kernel contains carbohydrates (70%), protein (12%), water (12%), fat (2%), crude fiber (2.2%), and minerals (1.8%), respectively. Moreover, wheat grain kernel is a potential source of minerals, including magnesium, phosphorus, zinc, manganese, iron, selenium, copper, and potassium [26]. Likewise, wheat is also enriched with a wide range of bioactive compounds, including phenolic acids (136.8–233.9 μg/g), alkylresorcinols (AR) (99.9–316.0 μg/g), phytosterols (562.6–1035.5 μg/g), and tocols (19.3–292.7 μg/g) [27, 28]. Phenolic acids are widely distributed in different parts of grains, i.e., testa, pericarp, and aleurone [29]. In wheat, several phenolic acids are present such as chlorogenic acid, ferulic acid, caffeic acid, *p*-coumaric, and sinapic acid, respectively. These compounds are present as bound forms, respectively, as phenolic acids (85%) in maize, wheat and maize (75%), and rice (62%). Cinnamic acids have been categorized as bioactive ingredients of the diet because they are bound to structural compounds of the cell wall

[30, 31]. The schematic representation of wheat grain fractions is shown in **Figure 1**.

Ferulic acid (4-hydroxy-3-methoxycinnamic acid) is present in different parts of vegetables, fruits, and grains as well as also endorses the health-promoting perspectives [29, 32]. Wheat flour is the prime ingredient, which is used to prepare different products of bread industry such as pasta. Wheat is also a promising source of dietary fibers along with preventing and curing some digestive disorders [33]. Endosperm is separated from the bran and germ through grinding, sieving, and purifying steps in conventional wheat roller milling. Furthermore, endosperm is also grounded to wheat flour on the basis of refinement and then used to prepare the bread, whereas bran, aleurone layer, starchy endosperm, and germ are used as milling by-products. Similarly, wheat bran is used by animals due to higher nutritional profile which exerts beneficial physiological effects. The bran-based products are shown with more health perspectives when

**Figure 1.** Schematic representation of wheat grain fractions.

368 Wheat Improvement, Management and Utilization

Wheat polyphenols are generally involved in defense mechanism against biotic and abiotic stresses which are secondary metabolites [35]. The first substrate of the phenyl propanoid pathway is phenylalanine, which initiates the biosynthesis of phenolic acids and then produces the different phenolic acids and flavonoids [36]. Similarly, wheat phenolic compounds are categorized into derivatives of hydroxybenzoic acid or hydroxycinnamic acid. In hydroxybenzoic acid derivatives, different compounds are present like gallic, vanillic, *p*-coumaric, hydroxybenzoic, and syringic acids, whereas hydroxycinnamic acids contain different derivatives, such as ferulic acid, dehydrotrimers of ferulic acid, *p*-coumaric acids, and dehydrodimers [37, 38].

Wheat antioxidants are located in wheat grain compartments such as the endosperm, bran, and germ [37]. The intermediate layer of wheat grain mostly composed of arabinoxylan and high amounts of ferulic acid monomers, whereas aleurone layer has lower content of ferulic acid dimers and trimers [39]. The phenolic contents present in bran/germ have 15–18 folds higher than that of endosperm, whereas only 17% of the total phenolic content is present in starchy endosperm [40, 41]. The phenolic compounds and antioxidant in wheat grain are shown in **Figure 2**.

**Figure 2.** Phenolic compounds and antioxidant in wheat grain.
