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

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 concentration of chlorogenic acids.

## **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 for the free acids, they performed an extraction with 80% ethanol using a high-performance disperser, then the residue was assisted by adding an enzyme cocktail (pectinases, amylases and cellulases). To the residue of this, they made a thermal hydrolysis doing another extraction with methanol and 70°C. Finally, to the solid residue of this extraction, they added NaOH to carry out a basic hydrolysis [55].

The effect of antioxidant activity on corn from Bajio and Morelos (Mexico) has been evaluated; wherein the amount of free and bound phenols was measured; concluding that the antioxidant activity increases three times more in the extractions with basic hydrolysis. Therefore, antioxidant increase is attributed to phenolic acids linked mainly to phenolic acid [31]. In other studies, they reported that one-third of the antioxidant activity of the phenolic fraction in Mexican pigmented corn is given by ferulic acid [24]. They have also described the antioxidant activity between phenolic compounds, reporting that the highest antioxidant activity is generally presented by hydroxycinnamic acids, with ferulic acid presenting the highest and hydroxybenzoic acids less activity. In the case of purple and pink corn silk [35], high antioxidant activity is attributed mainly to chlorogenic acids, these activities being so high that they could be compared with other medicinal plants such as *Mentha piperita* and *Salvia officinalis*.

Bioactive Compounds in Pigmented Maize http://dx.doi.org/10.5772/intechopen.78340 83

Other import group of the bioactive compounds that contain the pigmented corns are of flavonoids; with>4000 compounds, these molecules are most abundant polyphenols present in plant foods. They are characterized by a 15-carbon skeleton, organized as C6-C3-C6, with different substitutions making up the different subclasses. The major groups of the flavonoids

The most common chemical structures of flavonoids in corn are shown in **Figure 6**, and the

Peruvian purple corn has kaempferol and morin as major flavonoids in kernel (**Table 8**), the concentration is 202–224 mg/100 g [53] which represent almost the total flavonoids (**Table 9**); after kaempferol and morin the naringenin glucoside and in minor amount rutin and quercetin. Meanwhile, Serbian pigmented corn phenotypes [35] report a lower total flavonoid

Flavonoids are the main bioactive compounds in pigmented corn silk [35] as shown in **Table 9**. Some authors reports until 3644.9 mg/100 g in Serbian purple corn and Mexican pigmented corn reports 797.1 a 2602.4 mg/100 g [61]. Among the flavonoids identified and quantified in pigmented corn silk is the maysin with 12.6–17.1 mg/100 g [35], quercetin (1.58 mg/100 g) and

Other organ of pigmented corn (blue, red and red dark) which represent higher concentration of total flavonoids is pollen (916.36–1087.69 mg/100 g) **Table 9**. The flavonoids identified are

**4. Flavonoids in pigmented corn**

**4.1. Flavonoids in pigmented corn kernel**

concentration with 19.90–33.75 mg/100 g.

**4.2. Flavonoids in pigmented corn silk**

narigenin glucoside (6.45 mg/100) [21].

**4.3. Flavonoids in pigmented corn pollen**

(**Table 8**) hyperoside, rutin and quercetin [60].

of nutritional interest are the flavonols or catechins [59].

composition of flavonoids in different parts of is presented in **Table 7**.

In the case of phenolic acids present in corn silk, they only report extractions with organic solvents; for example, performing a direct extraction of the silk, using 95% methanol, centrifuging and using the supernatant for quantification and characterization [35]; other studies use 50% ethanol [21]. In the same way, for the case of the phenolic acids of the cob where they describe a simple extraction using methanol and centrifugation [32].

To carry out the characterization and quantification of each of the phenolic acids perform chromatography techniques: such as HPLC and HPLC-MS [52–55].

#### **3.5. Biological activity of pigmented corn phenolic acids**

The phenolic acids present in the pigmented corns are of great importance due to the biological effects on human health [56], such as anticancer properties, antimutagenic, anti-inflammatory and cardiovascular diseases [56]. **Table 6** shows the biological properties of each of the phenolic acids present in the pigmented corn plant.

The biological activity that most report is as antioxidant, with phenolic acids having the capacity to reduce the free radical formation and elimination of ROS, inhibition and repair of lesions caused by the oxidation and degradation of other molecules and biomolecules [57].


**Table 6.** Phenolic acids present in pigmented maize and their biological properties.

The effect of antioxidant activity on corn from Bajio and Morelos (Mexico) has been evaluated; wherein the amount of free and bound phenols was measured; concluding that the antioxidant activity increases three times more in the extractions with basic hydrolysis. Therefore, antioxidant increase is attributed to phenolic acids linked mainly to phenolic acid [31]. In other studies, they reported that one-third of the antioxidant activity of the phenolic fraction in Mexican pigmented corn is given by ferulic acid [24]. They have also described the antioxidant activity between phenolic compounds, reporting that the highest antioxidant activity is generally presented by hydroxycinnamic acids, with ferulic acid presenting the highest and hydroxybenzoic acids less activity. In the case of purple and pink corn silk [35], high antioxidant activity is attributed mainly to chlorogenic acids, these activities being so high that they could be compared with other medicinal plants such as *Mentha piperita* and *Salvia officinalis*.
