**3. Phenolic acids in pigmented corn**

Pigmented corns are good source of phenolic acids; mainly hydroxycinnamic acids but also hydroxybenzoic and chlorogenic acids. These compounds are distributed in whole plant. **Table 4** shows the main phenolic acids found in different parts of the plant reported in the literature (**Figure 5**).

In white, yellow and pigmented maize, ferulic acid is the most abundant phenolic acid. There are reports that in white and yellow corn it can be found in the forms of dimers, trimers and tetramers [51]. Other authors have reported 1.94 mg/100 g [52] of free diferulic acid in blue Mexican corn which is the most abundant in that variety (**Table 5**).

#### **3.1. Phenolic acid in pigmented corn kernel**

Free ferulic acid concentration in a variety of pigmented kernel is similar among Mexican and Khao Niew Dum varieties (2.02–3.99 mg/100 g) [24, 52]; however, Peruvian variety has the highest concentration with 5.50 mg/100 g [53].

Also, there are reports that evaluate ferulic concentration among different Mexican corn phenotypes pigmented white and yellow and there are no statistically significant differences. The concentration is between 140 and 160 mg and 94–98% are bounded in cell wall and the rest is free [24]. In the cell wall, ferulic acid plays an important role because it is cross-linked through photochemical reactions or coupling reactions catalyzed by peroxidases with the polysaccharides present in the grains, thus improving the rigidity in the cell

Bioactive Compounds in Pigmented Maize http://dx.doi.org/10.5772/intechopen.78340 81

Other acids found in pigmented maize kernel are as follows: *p*-coumaric, caffeic, vanillic, chlorogenic and hydroxybenzoic acids, however concentrations are different according to the variety. In purple maize variety Khao Niew Dum, the next acid apart of the ferulic acid are *p*-coumaric, vanillic, caffeic and *p*-hydroxybenzoic acid [54]; while in INIA-GUI purple corn from Peru, the acid with major concentration after ferulic acid is the caffeic acid and cholorogenic acid [53]. The difference in concentration could depend on different factors as genetic,

Research about pigmented corn cob is low; nevertheless, they have concentrations of important phenolic acids. The most abundant phenolic acid in cob from four pigmented corn phenotypes is syringic acid (31–202.78 mg/100 g) [32], followed by ferulic acid (7.34–10.73 mg/100 g) and in minors amounts vanillic acid (1.42–7.05 mg/100 g) and hydroxybenzoic acid

Other organ from maize plant which has been studied due to their higher concentration of phenolic acids, in particular chlorogenic acids, is the stigma, commonly called silk. Some authors highlight that silk from purple corn have 25.64 mg/100 g of chlorogenic acid [21] and other studies highlight that from 25 days after emergence from four phenotypes of corn (purple, green, pink and yellow) they have 21.2–29.3 mg/100 g of 3-caffeoylquinic acid, and 5 days after emergence 923.7–1840.8 mg/100 g [37], also other three chlorogenic acids where studied: 4-caffeoylquinic acid (186.9–362.1 mg/100 g), 5-caffeoylquinic acid (74.4–86.5 mg/100 g) and *p*-coumaroylquinic acid (43.4–90.9 mg/100 g). Purple and green silk has the major concentra-

**3.4. Extraction methods and characterization of phenolic acids in pigmented corn**

As already mentioned, most of the phenolic acids in the corn kernel are bound to the cell wall and a minimum amount are free form; for this reason, the way to extract them to identify and quantify them is not simple and is diverse: some authors point to the extraction of free phenolic acids, making an extraction with 80% methanol and centrifuging [31]; while the solid of the methanol extraction was carried out by a basic hydrolysis (with NaOH) with a water bath at 80°C for 30 min, and in this way the acids bound to the cell wall are obtained. Other authors report successive extraction methods for the recovery of free and bound phenolic acids; first

environmental, ripening, light-UV exposure and insect and pathogens attack [51].

wall of corn [51].

(0.73–7.05 mg/100 g).

tion of chlorogenic acids.

**3.2. Phenolic acid in pigmented corn cob**

**3.3. Phenolic acid in pigmented corn silk**

**Figure 5.** Phenolic acids structures in pigmented corn.


**Table 5.** Free phenolic acid concentration in different phenotypes of pigmented corns.

Also, there are reports that evaluate ferulic concentration among different Mexican corn phenotypes pigmented white and yellow and there are no statistically significant differences. The concentration is between 140 and 160 mg and 94–98% are bounded in cell wall and the rest is free [24]. In the cell wall, ferulic acid plays an important role because it is cross-linked through photochemical reactions or coupling reactions catalyzed by peroxidases with the polysaccharides present in the grains, thus improving the rigidity in the cell wall of corn [51].

Other acids found in pigmented maize kernel are as follows: *p*-coumaric, caffeic, vanillic, chlorogenic and hydroxybenzoic acids, however concentrations are different according to the variety. In purple maize variety Khao Niew Dum, the next acid apart of the ferulic acid are *p*-coumaric, vanillic, caffeic and *p*-hydroxybenzoic acid [54]; while in INIA-GUI purple corn from Peru, the acid with major concentration after ferulic acid is the caffeic acid and cholorogenic acid [53]. The difference in concentration could depend on different factors as genetic, environmental, ripening, light-UV exposure and insect and pathogens attack [51].
