**3. Nutraceutical properties of corn**

The kernel of corn contains proteins that have been classified into four groups in relation to their solubility. The most water-soluble proteins fall into the category of albumins, while proteins soluble in saline solutions are known as globulins. Proteins soluble in alcoholic solutions make up the group of prolamins or zeins, and proteins unable to be solubilized in any of the previous solutions form the group of glutelins. In view of this, the disposition and location of these proteins have a differential characteristic. For example, albumins and globulins are located mainly in the germ, while prolamins and glutelins can be found predominantly in the endosperm. In relation to their concentration, proteins are distributed unevenly in the corn kernel; 40% of the proteins are concentrated in zeins, followed by the glutelins, with 30%, and globulins and albumins together representing less than 5%. Of these, approximately 60% of the proteins are concentrated in the endosperm and are prolamins, with α-zein being the most abundant in corn, reaching up to 75% of the total prolamins [17]. Due to the water insolubility of corn proteins, its potential health benefits are limited; however, late technological advances have allowed to obtain peptides by hydrolysis in order to improve their bioavailability [18].

Once ingested, corn proteins are hydrolyzed by the activity of gastrointestinal enzymes such as pepsin, trypsin, and chymotrypsin. In vitro, this process can be carried out by the addition of enzymes, or by acidification or fermentation. Nonetheless, in vitro hydrolysis processes have shown some drawbacks, for example, when using acids, controlling the process can be complicated and some amino acids can be lost; also, protein hydrolysis turns out to be inefficient under the process of fermentation. As of late, enzymatic digestion has been chosen for in vitro isolation of bioactive peptides, which has proven to be a more efficient process. From two-amino acid peptides to 30-amino acid polypeptides can be isolated by means of these processes. Hydrophobic amino acids can be counted among peptides with bioactive capacity, structured with a positive charge and a proline in their C-terminal end [19]. On the other hand, dipeptides and tripeptides have greater resistance to the degradation of stomach, pancreatic, and intestinal proteases and peptidases, and larger peptides (six amino acids and larger) have a higher biological activity outside the intestine [20].

improvement is not limited only to the kernel or its byproducts [13]; other anatomical parts of the plant such as stigmata, cobs, and leaf sheaths have proven to be an important source of

Corn kernels consist mainly of fiber, ranging from 61 to 86%, depending on the variety of the plant. Approximately 99% of the fiber is found in the endosperm and consists of starch (approximately 73% of the total weight), and the rest of resistant starch. The kernel also contains non-starch polysaccharides such as cellulose, hemicellulose, and, to a lesser extent, lignin (approximately 10% of the total weight), located mainly in the brand. Protein follows; depending on the variety of corn, it can range from 6 to 12%, calculated on the dry basis, while lipids represent around 3–6%. Out of these, between 81 and 85% is stored in the germ. Other phytochemical elements can also be found in pigmented and yellow varieties, in the form of secondary metabolites, phenolic compounds, and carotenoids for the most part. A very wide range of phenolic content exists among corn varieties, which has been assessed by the quantification of total polyphenols under the Folin–Ciocalteu reagent method, reporting amounts of 1756 mg of gallic acid equivalent/100 g of sample for a variety of purple corn with Andean genotype [14] and 266 mg gallic acid equivalent/100 g of sample for varieties of purple corn with Mexican genotype [15]. When it comes to Mexican white corn, amounts of 260 mg of gallic acid equivalent/100 g of sample have been reported; likewise, it is likely that corn types with a high profile of carotenoids contain a higher concentration of phenolic compounds, reporting 320 mg of gallic acid equivalent/100 g of sample [15]. It should be noted that yellow corn varieties have reported the highest carotenoid content, with an average dry base concentration of 13 μg of β-carotene equivalent/100 g of sample [16],

These elements act as nutraceuticals depending on their bioavailability, molecular structure, physicochemical characteristics, and their physiological effects, as well as on the properties

The kernel of corn contains proteins that have been classified into four groups in relation to their solubility. The most water-soluble proteins fall into the category of albumins, while proteins soluble in saline solutions are known as globulins. Proteins soluble in alcoholic solutions make up the group of prolamins or zeins, and proteins unable to be solubilized in any of the previous solutions form the group of glutelins. In view of this, the disposition and location of these proteins have a differential characteristic. For example, albumins and globulins are located mainly in the germ, while prolamins and glutelins can be found predominantly in the endosperm. In relation to their concentration, proteins are distributed unevenly in the corn kernel; 40% of the proteins are concentrated in zeins, followed by the glutelins, with 30%, and globulins and albumins together representing less than 5%. Of these, approximately 60% of the proteins are concentrated in the endosperm and are prolamins, with α-zein being the most abundant in corn, reaching up to 75% of the total prolamins [17]. Due to the water insolubility of corn proteins, its potential health benefits are limited; however, late technological advances have allowed to obtain peptides by hydrolysis in order to improve their bioavailability [18].

acquired or lost after the different food byproducts have been processed.

nutraceutical molecules, as will be seen later in this chapter.

32 Corn - Production and Human Health in Changing Climate

although red varieties also synthesize carotenoids.

**3. Nutraceutical properties of corn**

Studies have shown that bioactive peptides can have beneficial effects on health, mainly as antihypertensive, anticholesterolemic, antioxidant, anti-inflammatory, anticarcinogenic, antimicrobial, and others, due to their immunomodulatory properties. Likewise, it has been reported that they can help decrease the effects associated with high alcohol consumption. A large number of bioactive peptides have been obtained by means of the hydrolysis of zeins proteins, for example, the tripeptide lysine-proline-proline, and from the γ-zein protein, the valine-histidine-leucineproline-proline-proline polypeptide, whereas the tripeptide proline-arginine-proline, which has also shown a biological functional activity, has been isolated from the α-zeins protein, as well as MBP-1 peptides from the corn kernel. Successful efforts have been made to isolate other peptides from corn gluten meal, such as Cys-Ser-Gln-Ala-Pro-Leu-Ala or Tyr-Pro-Lys-Leu-Ala-Pro-Asn-Glu. Overall, it has been observed that a large number of peptides can be isolated from the different components of corn, although their possible biological activity is still undergoing further research, as it is still necessary to carry out studies that help find the mechanisms from which these peptides can exert their biological activity.

As for the total fiber contained in corn, resistant starch is a type of non-digestible fiber, as it is highly resistant to the activity of digestive enzymes. The presence of resistant starch seems to be directly related to the percentage of amylose content. In normal corn, the presence of 34% of amylose is related to 0.8% of resistant starch, while high-amylose corn starch, the recorded presence of 83% amylose results in 39% resistant starch [21, 22]. However, resistant starch can be metabolized by the microbiota of the large intestine through fermentation and this in turn results in small chains of fatty acids [23]. Both the starch and the resistant starch contained in corn kernels have grown in relevance due to their possible function as regulators of body weight, thus a possible natural alternative for the treatment of obesity. On the other hand, these elements have also been linked to liver protection and the prevention of type 2 diabetes [24, 25].

In turn, phenolic compounds are a group of molecules whose chemical structure is made up of several hydroxyl groups linked to an aromatic group. When two or more rings are conjugated, a polyphenolic structure is generated; depending on the number of aromatic rings and the structural elements that bind them together, thousands of polyphenols have been identified. The polyphenols synthesized in corn can be classified into three groups according to their concentration and their contribution to human health; this way, we can speak of non-anthocyanin flavonoids, phenolic acids, and anthocyanin flavonoids. The group of non-anthocyanin flavonoids includes flavonols (rutin, isoquercetin, flavonol, morin, kaempferol, and quercetin) and flavonones (naringenin and hesperetin) [26], while the phenolic acids found in corn are protocatechuic acid, vanillic acid, syringic acid, trihydroxybenzoic acid, caffeic acid, chlorogenic acid, and p-hydroxyphenylacetic acid. Ferulic acid and p-coumaric acid are the compounds with more concentrates in corn, particularly in pigmented varieties [27, 28]. Total ferulic acid content detected in kernels of white varieties with Mexican genotype has been reported as 124,053 mg of ferulic acid equivalent/100 g of sample, while pigmented varieties such as blue or red corn have reported 129,985 and 130,297 mg of ferulic acid/100 g sample, respectively [15].

to 60 μg of xanthophylls equivalent/g of sample [39]. Carotenoids are found mainly in the germ, followed by the aleurone and the endosperm. Generally, by decreasing lipoperoxida-

Tissues such as stigmata, cobs, stems, and leaf sheaths of corn can be an important source of anthocyanins, ferulic acid, and some other substances that may help improve health; even when those are not products fit for human consumption, they could be processed to obtain extracts with a potential nutraceutical use. As of today, there is scientific evidence of the use of stigmata for the treatment of conditions such as kidney disorders, hypertension, and some neurodegenerative diseases. Some of the bioactive compounds that can be isolated from these tissues are terpenoids, steroids, saccharides, cerebrosides, flavonoids such as flavonones and

Reactive oxygen species (ROS) are a group of molecules derived from oxygen that are characterized by their high reactivity and a short life span. The reactivity of these molecules is due to the presence of two unpaired electrons in the outermost electron layer. Among the molecules

intracellular mechanisms. The main source of ROS is the mitochondria during the cellular respiration process, followed by cellular metabolism processes, whereas exogenous production of ROS arises from smoking, ultraviolet radiation, ionizing radiation, drug consumption, and the presence of toxins. The damage generated by ROS is due to their reductive property, and if not properly regulated, they can alter cell integrity due to the peroxidation of lipids and

Oxidative stress is generated by excess ROS, linked to cell damage associated with chronicdegenerative diseases such as cancer, chronic inflammation, cardiovascular diseases, neurodegenerative problems, and metabolic dysfunction. The process of cellular oxidation is regulated by antioxidant mechanisms, which delay or prevent the formation of ROS. Antioxidant protection is achieved through the correct balance between pro-oxidants and endogenous and/ or exogenous antioxidants. Cells have an endogenous system of enzymes such as superoxide dismutase (SOD), catalases (CAT), glutathione peroxidase (GPx), quinone reductase (QR), and glutathione reductase (GR), which function as ROS stabilizers [42]. Compounds with antioxidant activity can be introduced in the body through diet, and corn is one important

Fruits, vegetables, and seeds in general contain a great diversity of antioxidants that can act for the benefit of health more efficiently than some synthetic antioxidants. Recent studies have shown that the consumption of cereals can provide a greater antioxidant activity [2600–3500 μmol of Trolox equivalent (TE)/100 g] compared to some fruits (1200 μmol of TE/100 g) or vegetables (450 μmol of TE/100 g). Carotenoids, bioactive peptides, and flavonoids such as corn anthocyanins can act as antioxidant agents by lowering ROS levels, or by activating endogenous antioxidant systems that reduce cell damage. The antioxidant activity of nutraceuticals in corn is different; for example, when assessing the antioxidant activity of the carotenoids of Croatian genotype corn through the ABTS technique, values of

proteins of the cell membrane, being able to even damage the structure of DNA.

−

). ROS can be generated by endogenous, extracellular, and

), the hydroxyl radical (OH<sup>−</sup>

The Maize Contribution in the Human Health http://dx.doi.org/10.5772/intechopen.78700

),

35

tion, carotenoids can act as antioxidant agents in lipid environments.

included in the ROS group are the superoxide free radical (O2

O2

anthocyanins, and lignan [40, 41].

**3.1. Antioxidant properties of corn**

and the hydrogen peroxide (H2

source of such compounds.

The food industry has exploited the varieties of yellow and white corn for a long time now; however, the use of pigmented varieties has gained more and more strength in the food sector recently, not only as a possible source of natural edible pigments but also for its properties as a functional food. Among the most common colors, red, blue, and black can be found. This pigmentation is conferred by anthocyanins. Anthocyanins are a group of natural pigments soluble in water, widely distributed in the different tissues of the plant. Anthocyanins are responsible for conferring shades ranging from red to blue and purple. Functionally, anthocyanins protect the plant from damage by radiation, partake in the defense against pathogens and/or predators, and in reproductive functions as pollinator attractants; likewise, they regulate the synthesis of growth factors such as auxin. In corn kernels, anthocyanins are stored mainly in the aleurone layer; it is also possible to find these molecules in the pericarp, or in both structures. Even native non-pigmented varieties, pure lines, and hybrids have some pigmented tissue in the roots of the seedling or anthers [29–31]. In pigmented corn, the content of anthocyanins can be evaluated as low, medium, and high, with values that range between 5.9 and 3045 mg of cyanidin-3-glucocide equivalent/100 g of sample, while values reported in white or yellow corn varieties range from 0.9 to 1.2 mg of cyanidin-3-glucocide equivalent/100 g [32, 33]. It is also possible to find anthocyanins in other tissues such as cobs and leaf sheaths, but the concentration in these structures is not precisely defined. Some studies have been found concentrations ranging from 430 to 11,700 mg of cyanidin-3-glucocide equivalent/100 g of sample for the cob [33], whereas for the leaf sheaths, it has been possible to extract up to 17,7900 mg of cyanidin-3-glucide equivalent/100 g of sample [34]. It should be noted that cyanidin and its derivates are more abundant in pigmented corn varieties [35].

Carotenoids are natural pigments in corn and other plants, responsible for conferring colorations ranging from yellow to orange. Carotenoids participate in functions such as photosynthesis due to their ability to absorb light from different spectra and transfer energy to chlorophyll. The carotenoids have a skeleton made up of 40 carbons of isopropene units. These structures can be cycled in one or both terminations, having several levels of hydrogenation or can have oxygenated functional groups and, according to this, can be classified into carotenes, which are tetrapenoid hydrocarbons, consisting solely of carbon and hydrogen atoms, and xanthophylls or oxo-carotenoids, structures that contain at least one oxygen. Yellow corns contain lutein, zeaxanthin, β-cryptoxanthin, and β-carotenes [36, 37]. Carotenoid concentration can vary widely depending on genotypes and external characteristics. For example, the blue variety of the Mexican genotype has concentrations of 0.18 μg of β-carotene equivalent/g of sample [38], while the yellow variety of the Canadian genotype has concentrations of up to 60 μg of xanthophylls equivalent/g of sample [39]. Carotenoids are found mainly in the germ, followed by the aleurone and the endosperm. Generally, by decreasing lipoperoxidation, carotenoids can act as antioxidant agents in lipid environments.

Tissues such as stigmata, cobs, stems, and leaf sheaths of corn can be an important source of anthocyanins, ferulic acid, and some other substances that may help improve health; even when those are not products fit for human consumption, they could be processed to obtain extracts with a potential nutraceutical use. As of today, there is scientific evidence of the use of stigmata for the treatment of conditions such as kidney disorders, hypertension, and some neurodegenerative diseases. Some of the bioactive compounds that can be isolated from these tissues are terpenoids, steroids, saccharides, cerebrosides, flavonoids such as flavonones and anthocyanins, and lignan [40, 41].
