Phytochemical Composition: Antioxidant Potential and Biological Activities of Corn Phytochemical Composition: Antioxidant Potential and Biological Activities of Corn

Corn seeds are used as a nutritional source for humans, and the stem and leaves are utilized as fodder for cattle throughout the world. Corn silk and corn cob are usu ally discarded as waste. This chapter highlights the nutritional as well as medicinal importance of various parts of corn plant. All parts of corn plant are good source of a variety of bioactive phytochemical compounds which possess antioxidant potential. The principal phytochemicals present in corn seed and corn silk include polyphenols, phenolic acids, flavonoids, anthocyanins, glycosides, carotenoids, and polysaccharides of biological importance, reducing compounds and some water-soluble vitamins. The presence of these phytochemicals makes corn a medicinal plant which shows various biological activities particularly the antioxidant, antimicrobial, antidiabetic, anti-obesity, antiproliferative, hepatoprotective, cardioprotective, and renal-protective activities. On the account of its high antioxidant potential, all parts of corn plant can be used for the management of oxidative stress and the treatment of various diseases.


Phytochemical composition
Phytochemicals are the non-nutritional bioactive compounds found in various parts of plants.
In plants these compounds perform vital functions particularly protection from predators and harsh environmental conditions. These compounds are also important in pharmaceutical and medicinal field due to their antioxidant, antimicrobial, and other biological properties. Flavonoids are the bioactive phytochemical compounds which make the plant resistant to the attack of microbes and insects and also protect the animals against various diseases [22][23][24]. Flavonoids possess strong antioxidant activity and free radical-scavenging capacity and inhibit protein glycation [23,25,26]. The antho cy anins have been found to protect against ischemic reperfusion injury in rats [27]. These have been also found to show antioxidant and antiradical activities which are further associated with certain health-promoting activities such as anticancer, anti-inflammatory, anti-obesity, antidiabetic, car dioprotective, and hepatoprotective activities [28][29][30]. Tannins are polyphenolic compounds which show several biological activities such as anti-inflammatory, antioxidant, free radical-scavenging, and antimutagenic activities [31,32].

Phytochemical components Reference
Corn stem

Antioxidant potential
The pharmaceutical and medicinal significance of medicinal plants is usually based on their antioxidant phytochemical composition. Antioxidants are the substances which have the ability to prevent the oxidation reactions in living and nonliving systems. They possess hydrogendonating ability due to which they reduce other species and are themselves oxidized. These substances perform their action by reducing the reactive oxygen or nitrogen species or metals in their oxidized forms. These substances have the ability to terminate the free radical chain reactions occurring in the living system. Owing to their antiradical and reducing properties, the antioxidant phytochemicals play a key role in the preparation of pharmaceutical formulations against various diseases. The diversity in the phytochemical quality and high content of bioactive antioxidant phytochemicals make corn a valuable candidate for pharmaceutical application. Among various parts of corn, the corn silk is a rich source of antioxidant compounds and possesses strong antioxidant potential. The antioxidant properties of various parts of corn studied in terms of total antioxidant activity, ferric reducing, iron chelating, copperreducing properties, and free radical-scavenging capacities are presented in Tables 3-5. The corn extracts have been also reported to improve the antioxidant status of various organs by affecting the activity of antioxidant enzymes [38]. TAOA, total antioxidant activity; β-CABC, β-carotene-bleaching capacity; GAE, gallic acid equivalent; TE, Trolox equivalent; AAE, ascorbic acid equivalent; fw, fresh weight; dw, dry weight.

Biological activities
Epidemiological studies have demonstrated a relationship between the consumption of food with high quantities of phenolic compounds and a reduction in the risks of chronic and degenerative diseases, such as cancers and cardiovascular disease. Corn seed possesses antidiabetic, antioxidant, antiproliferative, and anti-cataractogenic activities [18,[39][40][41].

Corn part
Extracting solvent

Activity Reference
Corn silk

Water
Diuretic and kaliuretic activity with reduced glomerular function, anti-hepatocarcinomic, antiadipogenic, antiobesitic, antihyperglycemic, antidiabetic, lipid lowering, hematinic, anti-inflammatory, and analgesic activity [43,55,59,99,100] Hot water Antioxidant activity and inhibition of IgE antibody formation in mice [48,101] Methanol Antioxidant, antimicrobial, anti-hyperthyroidism, inhibition of lipid peroxidation, immunomodulatory activity by enhancing the innate immunity, lipid lowering, and cardioprotective activity [19,47,49,102,103] Ethanol Inhibition of tumor necrosis factor-α and adhesion of leukocytes to cell surface, activation of human peroxisome proliferator activator receptors, induction of antioxidant enzymes, and reduction of oxidative stress, antioxidant and free radical-scavenging, urease inhibitory, antihyperlipidemic, and diuretic activity [34,38,44,46,50,76,104] Aqueous alcohol Anti-fatigue, hepatoprotective, and renal protective activity in terms of inhibition of lipid peroxidation [10,37,[105][106][107][108] Aqueous acetone Antioxidant activity [20] Various polarity solvents Antioxidant activity in terms of free radical-scavenging, metal-reducing and beta-carotene-bleaching capacities and antimicrobial activity [24,87,109] Corn silk powder Antioxidant and immunostimulatory activity in fish [110] Phytochemical Composition: Antioxidant Potential and Biological Activities of Corn http://dx.doi.org/10.5772/intechopen.79648 Corn silk has been traditionally used for the treatment of several ailments due to various pharmacological activities exhibited by its extracts. It has been found to possess antioxidant, antidiabetic, antiproliferative, antimutagenic, anticoagulant, antifungal, antiadipogenic, antiobesitic, antihypertensive, antihyperlipidemic, antilithiatic, antibiotic, antibacterial, antiseptic, anti-inflammatory, antidepressant, and anti-fatigue activities [6,11,34,38,42,43]. It has been also reported to possess antihyperglycemic, antihyperlipidemic, diuretic, neuroprotective, hepatoprotective, and uricosuric activities [44,45]. Corn silk has been investigated to activate the receptors for the binding of human peroxisome proliferator activators used in the treatment of diabetes [46]. Its methanolic extract has been found to be effective in thyroid dysfunction [47]. Corn silk extracts contain certain bioactive compounds which show immunomodulation activity [33,48,49]. Corn silk extracts have been also found to be effective in inhibition of tumor necrosis factor-α and adhesion of leukocytes to cell surface and induction of nitric oxide synthase and cyclooxygenase in macrophages [50][51][52]. The chemically modified corn silk polysaccharides have been reported to show antioxidant and amylase inhibitory activities [14]. Recently, the studies have shown that corn silk has no cytotoxic effect, but the excessive use of corn silk may be cardiotoxic particularly in patients with compromised cardiac health [4]. The biological activities of various extracts of different parts of corn are presented in Table 6.

Medicinal importance
Corn seed kernel is commonly used as nutritional purpose, but owing to its good phytochemical composition and biological properties, it has great medicinal value. The toxicological assessment of corn at various doses against various clinical parameters has proven it clinically nontoxic and can be used for nutritional and medicinal purposes [53]. Anthocyanins in purple waxy corn have been reported to be effective against diabetic cataract [39]. Corn silk is usually discarded as waste and not used for nutritional purpose. However, it has a great medicinal importance due to the presence of valuable bioactive phytochemical compounds. It has been traditionally used as an effective herbal remedy for the treatment of hyperglycemia, diabetes, obesity, hypercholesterolemia, hyperthyroidism, rheumatism, arthritis, gout,

Corn part
Extracting solvent

Activity Reference
Corn seed

Methanol
Antioxidant activity in terms of free radical-scavenging and metalreducing capacity [18,40] Aqueous alcohol Antioxidant and anti-cataractogenic activity against diabetic cataract [39] Corn stem

Ethanol
Nephroprotective activity by dose-dependent increase antioxidant enzymes in diabetic rat [111]  tumors, hepatitis, heart problems, jaundice, malaria, inflammation, asthma prostatitis, cystitis, nephritis, kidney stones, bed wetting, renal conditions, and other kidney-related diseases. Corn silk is also known to be urine laxative, antihypertensive, and immune enhancer. Corn silk tea has been used as diuretic for the treatment of urinal irritation. In combination with other herbs, corn silk has been found to be effective against mumps or inflammation of the bladder. It has been also reported to be useful in gonorrhea, acute and chronic cystitis, and bladder irritation due to uric acid and phosphate gravel [11, 14, 37, 38, 42-44, 46, 47, 51, 54-59]. Recently, corn silk polysaccharides have been suggested to be a good choice as functional food or medicine for the treatment of type 2 diabetes mellitus due to its hypoglycemic activity [60].

Factors affecting the phytochemical profile and antioxidant potential of corn
There are several factors which have been reported to affect the phytochemical quality and antioxidant potential of various parts of corn. The phytochemical composition and antioxidant profile of maize have been observed to be different in different varieties and at various stages of maturity [18,[61][62][63]. The phytochemical content of corn silk has been found to be enhanced by treatment with red algae [64]. The location, climatic, water stress, irrigation method, and plant density significantly affect the growth, metabolism, and physiological characteristics of corn plant [65][66][67]. The spraying of salicylic acid and collection period have been found to increase the growth rate and phytochemical content of corn silk [68]. The fermentation of corn samples has been found to result in an increase in carotenoid and ascorbic acid content with a slight decrease in antioxidant activity [69]. The germination conditions between light and dark periods have been also found to affect the morphological structures, biochemical and phytochemical composition, and antioxidant activity of corn sprouts [70]. The storage conditions, processing techniques, and cooking methods have been also found to affect the phytochemical content and free radical-scavenging activity of maize [21,71]. Recently, studies in our laboratory have shown that high-dose gamma irradiation results in a decrease in antioxidant properties of corn flour [72].

Conclusion
All parts of corn plant are good sources of phytochemical compounds which possess antioxidant potential. Corn seed have a valuable role in human nutrition, while corn silk has a great medicinal importance due the presence of a variety of bioactive phytochemical compounds. The principal phytochemicals present in corn silk include polyphenols, phenolic acids, flavonoids, anthocyanins, glycosides, carotenoids, and some water-soluble vitamins. The presence of these phytochemicals makes corn a medicinal plant which shows various biological activities particularly the antioxidant activity. On the account of its high antioxidant potential, all parts of corn plant can be used for the management of oxidative stress and the treatment of various diseases.