**3.1. Antioxidant properties of corn**

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]. 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

34 Corn - Production and Human Health in Changing Climate

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 included in the ROS group are the superoxide free radical (O2 − ), the hydroxyl radical (OH<sup>−</sup> ), and the hydrogen peroxide (H2 O2 ). ROS can be generated by endogenous, extracellular, and 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 proteins of the cell membrane, being able to even damage the structure of DNA.

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 source of such compounds.

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 0.767 μmol of TE/g of sample were reported [34], whereas the total extracts of Italian genotype corn have reported antioxidant activity of 29 μmol of TE/g of sample [43]. These data suggest that carotenoids only contribute approximately 5% of the total antioxidant activity, while the phenolic fraction has the highest antioxidant activity. It should be noted that the antioxidant activity of carotenoids depends on their concentration, their distribution in the kernel, and the type of carotenoid, as studies have found activity values of 71 μmol of TE/g of sample in extracts of aleurone and 66.2 μmol of TE/g of sample in the endosperm. Other studies measured the antioxidant activity of the carotenoids contained in corn tortillas with the β-carotene/linoleate bleaching method, showing that the nixtamalization process can improve the antioxidant activity of carotenoids. In tortillas made of Mexican genotype corn of red or blue varieties, a decrease in whitening of approximately 27% has been reported, while in unprocessed kernels, the value reported was 15%. A value of 25% has been reported for white corn tortillas and 12% for raw kernels [38].

antioxidant activity are the flavonoids, the anthocyanins being those that inhibit, to a greater extent, the formation of ROS, in a concentration-dependent manner. In addition to kernels, other tissues such as stigmata, leaf sheaths, and cobs, particularly those of pigmented varieties, stand out as potential sources for anthocyanins, showing a high antioxidant activity.

Another group of compounds that can be found in corn is that of bioactive peptides, exogenous antioxidants that can act as scavengers of free radicals, inhibitors of ROS formation, and promoters of the activation of endogenous antioxidant systems. It has been shown that from the peptide fraction of corn gluten, only the sequences of Gly-Leu-Leu-Leu-Pro-His and Tyr-Phe-Cys-Leu-Thr can exert their antioxidant activity through the reduction of the amount of ROS and regulate the activity of enzymes such as SDO, CAT, and GR [42]. Some peptides

electron donors. In spite of the scientific evidence demonstrating the antioxidant activity of corn bioactive peptides, it is still necessary to carry out further studies in biological models to explain their interaction in the organism. From the above, it can be concluded that corn and its byproducts not only represent a food source with a high nutritional value but also that, due to its anthocyanin, polyphenol, and peptide content, they contribute to the correct functioning and homeostatic maintenance of the organism. Moreover, due to its antioxidant properties, it can be used as an alternative to prevent the oxidative damage caused by stress and the

Obesity is currently a multifactorial etiology, chronic course disease, which involves genetic, environmental, and lifestyle aspects. Obesity is defined as the abnormal or excessive accumulation of fat harmful to health. One of the parameters that must be evaluated in order to determine if a person has obesity is the body mass index (BMI). Thus, a person with a BMI equal to or greater than 30 is considered obese. In recent years, obesity has been acknowledged as a global public health problem: an estimated 1900 million adults are overweight, and 600 million are obese [47]. Research carried out in rodents has shown that anthocyanins contained in purple corn can improve insulin resistance induced by a high-fat diet. For example, the cyanidin 3-glucoside present in purple corn may suppress the transcription of mRNA for the synthesis of enzymes involved in the production of fatty acids and triglycerides and reduce the sterol, a regulatory element that binds to the mRNA level of the protein-1 in white adipose tissue. The downregulation of protein-1 may contribute to the accumulation of triglycerides in white adipose tissue. These data, reported in 2003 by researchers from the University of Doshisha in Japan, have established the biochemical and nutritional bases for the use of cyanidin and anthocyanins in purple corn, as a functional food factor able to provide benefits for the prevention of obesity and diabetes [48]. Components of bioactive foods, such as resistant corn starch with a

high content of amylose type 2 and sodium butyrate, reduce obesity in rodents [24].

Recently, an integral version has been used in a study carried out on humans, demonstrating greater postprandial satiety [49]. In addition, in vitro studies have shown a potential anti-obesity effect of purple corn stigmata in multiple stages of the adipocyte life cycle. The potential effects of high concentrations of purple corn stigmata extracts may inhibit adipocyte

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The Maize Contribution in the Human Health http://dx.doi.org/10.5772/intechopen.78700 37

radical by acting as

synthesized from corn gluten meal can decrease the formation of the O2

subsequent negative effects associated with it.

**3.2. Corn and metabolism**

When comparing the antioxidant activity of phenolic compounds of pigmented corn and the polyphenols of blue berries, it was shown that corn has a greater antioxidant capacity and greater reaction kinetics [14]. When evaluating the antioxidant capacity in phenolic compounds of the blue, red, white, yellow, and high carotenoid corn varieties by the peroxyl radical scavenging capacity assay (PSC), an activity of 41–49 μmol of vitamin C equivalent/100 g of sample was reported [15]. This fact has proven that the higher the phenolic content, the greater the antioxidant activity, not only in kernels, but this quality is also maintained in byproducts elaborated by the nixtamalization process, such as the tortilla. However, unlike carotenoids, corn phenolic compounds are affected by production processes such as nixtamalization, which causes a decrease in their nutraceutical properties. For example, in Mexican phenotype corn kernels of the blue variety, a concentration of 343 mg of gallic acid equivalent/100 g of sample has been reported, while in products such as tortillas made with this same kernel, 201 mg of gallic acid equivalent/100 g of sample has been found. Antioxidant capacity can be expressed as the inhibition of ABTS cation formation; this way, it was determined that the antioxidant activity of the kernel is approximately 63%, while for the tortilla, it was 44%. The antioxidant activity of corn is not only limited to inhibiting the formation of ROS, it can also regulate cellular enzymatic elements for the defense against oxidative stress. It has been shown that corn components can increase the activity of the QR enzyme [44]. Only some of the phenolic compounds contained in corn have biological activity; for example, phenolic acids have only been able to recognize the nutraceutical capacity of compounds such as ferulic acid, protocatechuic acid, and p-coumaric acid [45].

Researchers from the University of Florida quantified and characterized the content of phenolic compounds in commercial genotype corn kernels of white varieties and of two blue varieties, one of Mexican genotype and the other North American, and reported a higher content of phenols in white corn, mainly ferulic acid, protocatechuic acid, and p-coumaric acid, while in blue corn, there were no traces of these acids. However, they found high concentrations of anthocyanins in the Mexican genotype, followed by the North American genotype. In addition, the antioxidant capacity of the three varieties was evaluated, demonstrating that the Mexican genotype has a greater capacity to inhibit the formation of ROS [46]. In this sense and due to their structural composition, the compounds contained in corn with a greater antioxidant activity are the flavonoids, the anthocyanins being those that inhibit, to a greater extent, the formation of ROS, in a concentration-dependent manner. In addition to kernels, other tissues such as stigmata, leaf sheaths, and cobs, particularly those of pigmented varieties, stand out as potential sources for anthocyanins, showing a high antioxidant activity.

Another group of compounds that can be found in corn is that of bioactive peptides, exogenous antioxidants that can act as scavengers of free radicals, inhibitors of ROS formation, and promoters of the activation of endogenous antioxidant systems. It has been shown that from the peptide fraction of corn gluten, only the sequences of Gly-Leu-Leu-Leu-Pro-His and Tyr-Phe-Cys-Leu-Thr can exert their antioxidant activity through the reduction of the amount of ROS and regulate the activity of enzymes such as SDO, CAT, and GR [42]. Some peptides synthesized from corn gluten meal can decrease the formation of the O2 − radical by acting as electron donors. In spite of the scientific evidence demonstrating the antioxidant activity of corn bioactive peptides, it is still necessary to carry out further studies in biological models to explain their interaction in the organism. From the above, it can be concluded that corn and its byproducts not only represent a food source with a high nutritional value but also that, due to its anthocyanin, polyphenol, and peptide content, they contribute to the correct functioning and homeostatic maintenance of the organism. Moreover, due to its antioxidant properties, it can be used as an alternative to prevent the oxidative damage caused by stress and the subsequent negative effects associated with it.
