**4.2. Pigmented maize grain**

### *4.2.1. Blue/purple grain*

Most of the ferulic acid in the pericarp of the maize grain is linked by ester bonds to cell wall polysaccharides [35]. Nonetheless, they are also present in the form of dehy‐ drodimers originating from the oxidative coupling of ferulate esters by means of the enzyme peroxidase. The diferulates that have been identified in maize grain are 8,5′‐dife‐ rulic acid, 8,O,4′‐diferulic acid, 8‐8‐diferulic acid, 4‐O‐5‐diferulic acid, and 5.5′‐diferulic acid [35], of which the most abundant is the first one [26]. The diferulates are linked to the arabinoxylans of the polymers that form the cell wall [36]. The resistance of the pericarp cells is attributed to the presence of these compounds and their abundance has been associated to resistance toward the development of fumonisins [37, 38] and tolerance to warehouse pests [15, 39]. The presence of ferulic acid dehydrotrimers was reported by Rouau et al. [40] in maize bran, which is a fraction that is composed of rem‐ nants of pericarp and aleurone layer. Until now, seven different ferulic acid dehydro‐ trimers have been identified [35]. The different ways in which ferulic acid is integrated into the cell wall components contributes to the formation of networks that support the resistance of this structure whose main function is to isolate and protect the grain from

224 Phenolic Compounds - Natural Sources, Importance and Applications

The type of maize affects the values reported for total soluble phenolics in the grain peri‐ carp. In dent maize grain, Cabrera‐Soto et al. [33] reported a variation of 232.4–334.0 mg EAG/g DW in seven different maize varieties. In cornpop, Das and Singh [18] observed a value of 13.1 ± 0.66 µmol of FAE/g of DW, while the value for QPM maize was of 15.9 ± 0.28. Insoluble phenolic content (IPs) in this structure is between 18 and 21 times that of soluble phenolics (SPs). Das and Singh [13] reported values of SPs of 11.9 and 10.4 µmol of FAE/g of DW in the pericarp of dent and crystalline maize types, respectively: the values of IPs were 218.6 and 219.4 µmol of FAE/g of DW, for the same maize grains. In the SPs fraction, the phenolic acids presented were vanillic, caffeic, ferulic, and p‐coumaric, with predominance of the latter; in IPs, ferulic acid represented between 40 and 50% of this

In maize grain with presence of anthocyanin pigments in the pericarp, the SPs content is commonly higher than the values observed in white maize grain. This is due to the presence of anthocyanins that occurred mainly in soluble form, because the amount of bounded antho‐

**Germ**. The germ concentrated the highest content of soluble phenolics of the maize grain structures. In seven varieties of white maize grain, Cabrera‐Soto et al. [33] reported in the germ values of 499.1–689.2 µg GAE/g DW; in the pericarp, the values were of 232.4–334.1 µg GAE/g DW, while in the endosperm, they reported values of 124.1–194.0 µg GAE/g DW. Meanwhile, Das and Singh [13] reported 14.2 ± 0.3 for germ, 11.9 ± 1.1 for pericarp, and 0.4 ± 0.02 µmol of FAE/g of DW, in one sample of dent maize grain. In the germ, the phenolic acids: 3‐hydroxy‐ benzoic acid, caffeic, p‐coumaric, ferulic in itsr cis and trans forms, and salicylic have been

**Endosperm**. The concentration of phenolic compounds in this structure is very low. Cabrera‐ Soto et al. [33] reported values of 124.1–194.0 µg GAE/g DW. The amount of IPs is also mar‐ ginal since it is less than 2% of that present in the pericarp and 3.56% of that contained in the

reported. Ferulic acid predominates in its esterified soluble form [41].

external agents.

fraction.

cyanins reported is very low [29].

The purple grain maize is the most studied with respect to the phenolic compounds because it is highly used for pigments extraction with application in foods [41–43]. In purple maize grain the phenolic acids have been reported: protocatechuic, vanillic, and p‐coumaric acid, besides four hydroxycinnamic acid derivatives [19]. Additionally, Ramos et al. [14] found in purple maize grain the following phenolic acids: chlorogenic, caffeic, and ferulic. Of the flavonoids present in purple maize grain, the anthocyanins are the most abundant. Ramos et al. [14] reported values of 2.76 ± 0.05 g of cyanidin‐3‐glucoside (C3G)/kg DW, meanwhile for flavonols and flavanols the values observed were of 0.41 ± 0.02 g of rutin equivalents (RE)/kg of DW and 0.23 ± 0.01 g of catechin equivalents (CE)/kg of DW, respectively. Other flavonoids described in this maize grain color were rutin, morin, quercetin, naringenin, and kaempferol. Others phenolic compounds that have been identified in purple maize grain are those result‐ ing from the condensation of flavanols (catechin or epicatechin) and anthocyanins. Some of these compounds are catechin‐(4,8)‐cyanidin‐3‐glucoside, catechin‐(4,8)‐peonidin‐3‐gluco‐ side, catechin‐(4,8)‐pelargonidin‐3‐glucoside, and the corresponding derivatives in which the epicatechin is the flavonol attached [44].
