Functional and Nutraceutical Based Applications of Phytochemicals from Major Cereal Grains

Farhan Mohiuddin Bhat*, Mamta Chandel, Nilakshi Chauhan and Yadwinder Singh Dhaliwal

CSK Himachal Pradesh Agricultural University, India *Corresponding author: Farhan Mohiuddin Bhat, CSK Himachal Pradesh Agricultural University, Palampur, HP, India, Tel: 6005570446; Email: farhanbhat999@gmail.com

Introduction

Cereal grains are staple foods sources of the world population and are important sources of nutrients and energy worldwide than any other crops [1]. Cereals are usually consumed as a whole or as an ingredient in food stuffs as a valuable source of proteins, carbohydrates, dietary fiber, carotenoids, B vitamins, and minerals along with phytochemicals including phenolic acids, flavones, organic acids, polyphenols, anthocyanins, sterols, tocopherols, tocotrienols, and phytosterols. The cereal grains provides high energy mainly due to the presence of starch in them but the fat and protein contents also contributed in energy generation. The starch composition in cereals varies from

65 to 75% of their total weight, proteins varied from 6 to 12% and fat from 1 to 5% along with moisture content, cellulose, traces of minerals and vitamins. Cereals are also rich sources of bioactive compounds, polyunsaturated fats like omega-3, linolenic acid, soluble and insoluble fibre, and resistant starches. The presence of phytochemicals in cereals makes them ideal for the formulation of functional foods and nutraceuticals due to their antioxidative, antimutagenic and anticarcinogenic activities [2]. The production of cereals is much greater than other types of crops throughout the world and thus is considered as the staple food crop [1]. Cereals are consumed by as a whole or as an ingredient in different formulation of food choices. Cereals are also fed to livestock and poultry that are usually consumed by human population in the form of meat, dairy and poultry products. Besides these, cereals are widely used in the industrial production of glucose, oils, adhesives, thickeners and alcohols. The nutritional elements in addition of chemical components that are present in small quantities usually in bran and germ part of cereal grains are called as bioactive compounds. These are having beneficial effect on health like antioxidant properties, anti-carcinogenic, antiinflammatory, anti-allergenic, anti- atherogenic and anti-proliferative activity, but are not regarded as essential for the human body [3], wheat, corn, rice, oats, rye, barley, buckwheat, sorghum, and millet as minor grains are the major cereals consumed globally, out of which wheat, corn, and rice are cultivated and produced much larger than other types of cereals [4].

Major Categories of Bioactive Compounds Present in Cereals

The bioactive compounds with widely variations in their chemical structures, properties and functions are often produced in small quantities either as primary metabolites or secondary metabolites such as terpenoids, polyphenols, vitamins, alkaloids [5]. These compounds are used for the formulation and fortification of functional foods and pharmaceuticals. The bioactive compounds are produced in specialized cell types during a particular growth stage and specific conditions that make extraction and purification of these compounds very difficult [6]. Phenolic compounds with one or more aromatic rings and contain one or more hydroxyl groups have been found to possess excellent antioxidant properties and thus protect the body from various degenerative diseases like cancer and coronary diseases [7]. Phenolic acids represent the hydroxylated derivatives of benzoic and cinnamic acid that includes both free and bound forms like p-hydroxybenzoic, protocatechuic, vanillic, capsaicin, ellagic, salicylic, tannic, vanillin, gallic, syringic, p-coumaric, o-coumaric, m-coumaric, caffeic, ferulic, sinapic, chlorogenic acids [8]. Flavonoids belonging to subclasses anthocyanins, flavonols, flavanones, flavones and flavonols are compounds having two aromatic rings joined together by three-carbon linkage. Carotenoids are pigments with more than 600 naturally occurring forms and gives yellow, orange, and red colors to different cereals. The carotenoids are focussing attention nowadays in the formulation of nutraceuticals and functional food due to their pro-vitamin and antioxidant properties. The carotenoids are mainly classified into two classes like carotene (β-carotene, γ-carotene, α-carotene and β-cryptoxanthin) and xanthophylls (lutein, astaxanthin and zeaxanthin). Β-Carotene, α-carotene and lycopene are mainly composed of carbon and hydrogen atoms whereas xanthophylls contain oxygen atoms. Xanthophylls consisting of Lutein, zeaxanthin and astaxanthin contain hydroxyl and keto groups in their structural conformations [9]. Among the carotenoids only β-carotene, γ-carotene, α-carotene and β-cryptoxanthin are converted to vitamin A (retinol). Carotenoids are considered best for their ability to scavenge free radicals by quenching of reactive oxygen species singlet oxygen, hydroxyl radical and superoxide anion. Among carotenoids lycopene has been found to retain higher antioxidant capability than β-carotene and lutein. The in-vivo antioxidant capability of carotenoids is mainly attributed for their ability to inhibit lipid peroxidation by extinguishing singlet oxygen. The antioxidant activity of β-Carotene has been found to be higher than vitamin E and vitamin C against the singlet oxygen radicals [10]. Β-carotene is regarded as a potent antioxidant for their role in preventing liver damage from toxic effects of drugs, photoprotective effects and anticarcinogenic activity whereas α-carotene has been found to be best for reducing the risk of cardiovascular disease and cancer. Β-Cryptoxanthin is more bioefficacious than α-carotene due to its bipolar nature along with its ability in reducing the risk of lung cancer. The carotenoids Lutein and zeaxanthin are stored in the retina and eyes of human body. Higher intake of these carotenoids leads to more than 20% reduction of cataract and 40% of age related macular degeneration [11]. Astaxanthin possess 10 times higher antioxidant activity than β-carotene and 500 times greater than vitamin E [12]. It also prevents the body from various toxic radicals, Ultra violet effects, LDL-cholesterol damage and tumours.

Functional and Bioactive Potential of Majorly Grown Global Cereals

Maize contains antioxidant rich carotene, xanthophylls, vanillic acid, ferulic acid, anthocyanins, phytoesterols, pantothenic acid and vitamins E, C and K [13].  These antioxidant rich compounds in maize have been to possess notable nutraceutical properties and health benefits including anti-obesity, anti-hypertensive, anti- prostatic, anti-fatigue, anti-inflammatory, and prevention of neurodegenerative disorders, anti diabetic and anti- carcinogenic activities [14]. The carotenoids prevalent in most of the yellow maize kernels have been found to be lutein, zeaxanthin, α and β cryptoxanthin while as lavorr- 3-glucoside, lavorr-3, 5-diglucoside, pelargonidin, and peonidin-3-glucoside are the major anthocyanins found in pigmented blue, red, and purple colored maize kernels [15]. Flavonoids being an important class of polyphenols comprise more than 4000 compounds in different types of corn varieties. The major class of flavonoids in corn have been found to be kaempferol, morin, rutin and quercetin. Corn has been found to contain thiamine that has been found to boost memory and neuronal health. The flavonoids in corn possess antibacterial, antiviral, antimicrobial, diuretic and hypertensive properties [16]. Xanthophylls in maize play an essential role in enhancing eye health by reducing the risk of age-related macular degeneration in optical muscles [17]. The presence of provitamin A carotenoids and xanthophylls in maize varieties have been found to be beneficial for the alleviation of vitamin A deficiency and oxidative stress.

Wheat is a rich source of bioactive phytochemicals including phenolic acids, tocopherols, carotenoids, phytosterols, alkylresorcinols, benzoxazinoids, and lignans. That has been associated with reduction of chronic health complications like type 2 diabetes, neurological disorders, cataracts, cardiovascular diseases, atherosclerosis and cancer. The highest concentration of bioactive phytochemicals are mostly concentrated in germ and bran fractions of the grain. Alkylresorcinols in wheat bran has been shown to inhibit platelet binding to fibrinogen, thereby stimulate thromboxane production and prevent triglyceride formation [18]. The most abundant phenolic acid in wheat grains has been found to be ferulic acid along with smaller concentrations of  p-hydroxybenzoic, vanillic, syringic, p-coumaric, salicylic, and sinapic acids [19]. About 80% of the phenolic acids in wheat grains are found in insoluble bound form in the bran fraction. The carotenoids Lutein and zeaxanthin are mostly predominant in whole wheat, with concentrations ranging from 0.5–1.44 and 0.2–0.39 µg/g of grain along with lower concentrations of β-cryptoxanthin. All of these components are having potential health benefits by inhibiting cholesterol biosynthesis thereby lowering LDL cholesterol levels along with increasing iron absorption in the human body [20]. The carotenoids are present in highest amount in the germ of the grain followed by the bran and endosperm fractions. The bran of wheat grain is an essential source of bioactive Ferulic acid that contributes antioxidant activity by the electron donation and hydrogen transfer to free radicals. In addition to ferulic acid, wheat grains also contains hydroxycinnamic acids coumaric, syringic, sinapic, salicylic and caffeic acid that are also having antioxidant activity [21]. The bran and germ of wheat grains exhibit beneficial positive effects to gut microbiota by providing indigestible fibers, resistant starch and nonstarch polysaccharides (β-glucan, inulin and arabinoxylans) and phenols that are metabolized by the residing microbiota and thus are having positive health benefits especially on gastrointestinal tract including diverticular disease, constipation and irritable bowel syndrome [22]. The significant bioactive compounds in wheat grains are phenolic compounds, beta-glucan, lignans, phytic acid, inositols and betaine that promotes its formulation for the development of functional foods. All of these components are associated with prevention of several diet and age- related diseases like increase in blood cholesterol, glycemic index, digestive and cardiovascular health, colon and breast cancers [23]. Majority of the bioactive compounds having antioxidant properties remain in bound form in the wheat grains that survive gastrointestinal digestion. Only 0.5% - 5% of the ferulic acid has been observed to be absorbed in the small intestine and this typical phenolic acid in wheat played an important role in the protection of the colon cancer [24]. The bran and germ fractions of the wheat grain were found to retain phytosterols, whileas steryl  ferulates  are mainly found to be present in the bran [25]. The higher concentration of pelargonidin and peonidin derivatives in pigmented wheat genotypes coupled with their excellent antioxidant properties makes them suitable for the development of functional foods. The phenolic compounds feruloyl oligosaccharides in wheat bran has been reported to protect human erythrocytes from free radical-induced oxidative damage [26].

Traditional cereal based formulations forms an important part of folk medicine since prehistoric times in China and India. These Traditional landraces possess nutritive and pharmalogical value and could be used in Ayurvedic and Unani system of medicines for treatment of various ailments. The traditional cereals have become a part of China’s cultural heritage and have received widespread popularity throughout the world [27].

An increased interest and attention are being paid to by both government and scientific bodies to reveal the various health-promoting benefits of these traditional cereals that could prove beneficial in relieving a number of chronic diseases. The cereals have been found to be rich source of phenolic and flavonoids [28]. These polyphenols act as reducing agents due to their ability to donate hydrogen atoms, also act as singlet oxygen quenchers and free radical hydrogen donors and because of these properties, they have protected the cell constituents against oxidative damage. The antioxidant properties of phenolics have been reported in epidemiological studies as anti-carcinogenic and prevent cardiovascular and nerve diseases [29].

Rice is the second largest cereal grain grown after maize that is consumed by majority of world population as their staple food [30]. Rice is mainly consumed in milled form as white rice. However, rice available in the form of pigmented rice have reddish, purple or even blackish colour. The main component of the rice is the starch present in the endosperm of the rice kernels. Starch consists of two main polymers amylose (AM) and amylopectin (AP), which determines the functional role of starch in the various food and non-food industrial application such as a thickening and binding agent, gelling and filling agent, emulsifier, clouding agent, photographic paper powder, in confectionary as sugar coating, in cosmetics as a dusting powder and expedient for pharmaceutical tablets [31]. The basic attributes associated with rice starch which preferred it over other cereal and non-cereal starches are non-allergenic , easy digestibility, bland lavor, small granule (3-10 μm), white colour, more acid resistance, greater freeze –thaw stability of pastes and a wide range of amylose/amylopectin ratios [32]. Pigmented rice consumption is rapidly increasing among the consumers due to their healthy prospective and considered as functional food ingredients. There are red and black paddy varieties which have about 38% more protein, about 18% more crude fiber and are richer in lysine, vitamin B1 and other minerals as compared to conventional rice varieties. In addition to good quality protein, high fiber content, and vitamin content, pigmented rice varieties are having functional properties due to the antioxidant compounds they contain and have the ability to inhibit the formation of reactive cell-damaging free radicals. Anthocyanin located in the bran layers of the rice kernel have been reported as a health promoting functional food ingredients, which possess anticancerous, antioxidant activity and anti-inflammatory property [33]. Keeping in view the several health benefits associated with anthocyanins, such as anti-inflammatory, anti-oxidative, and anticancer effects, pigmented rice is considered as a functional food and food ingredient in many Asian countries. Greater interest has been shown in these rice cultivars recently due to the polyphenols in this rice that are having multiple biological activities. These phenolic compounds have been found to consist of anthocyanidins, ferulic acid and diferulates, anthocyanins, and polymeric proanthocyanidins (condensed tannins). Phenolic acids are mainly present in the bran layers of riceexisting as free, conjugated, and bound forms. The bound phenolics present in rice bran amounted to more than 70% of the total phenolic and are having a higher antioxidant capacity than free phenolics. Pigmented rice varieties contain antioxidative compounds that are having the ability to inhibit the formation or to reduce the concentrations of reactive cell-damaging free radicals and thus have the potential to promote human health. These observations suggest that pigmented non polished rice varieties may have beneficial effects in the human diet. The application and incorporation of bran into food products for the preparation of functional foods is increasing due to presence of bioactive compounds. The superior antioxidant activities in pigmented bran and non-pigmented Gull zag could be attributed to their greater amount polar phenolic compounds such as thymol, quinicquinic-cafeic acid ester, tricafeoyl-hydroxyferulic acid, and Chlorogenic acid [34].

Barley (Hordeum vulgare L.) is the world’s fourth-largest cereal grain produced after wheat, rice, and corn, which could be classified into hulled barley and hull-less barley according to the presence or absence of the husk on the grain [35]. Approximately three-quarters of the worldwide barley production is used for animal feed, while 20% is malted for use in alcoholic and non-alcoholic beverages and 5% is used as a component in the production of so many food products [36]. It is available in different varieties such as hulled, hull- less, normal, waxy barley as well as low and high β-glucan barley. In India, its utilization as a food crop is restricted to the tribal areas of hills. The barley products have been used in ayurvedic medicinal form for treatment of various ailments, like “Sattu” that is consumed in summers because of its cooling effects on the human body [37].

Generally, Barley acts as a functional food due to its content of so many health-promoting components that have shown positive health effect such as β- glucan. These special characteristics of barley enable its use in the formulation of various kinds of functional foods. With the changing lifestyles and increasing urbanization, diseases like coronary heart disease, diabetes etc., are on the rise all over the world. Changes in dietary habits are one of the effective manners suggested preventing these diseases. Besides this, in the past few years, it has been shown that inclusion of nutraceuticals such as soluble dietary fibers can help in controlling the blood cholesterol and glucose levels besides providing benefits to gut health. Barley grains possess higher amounts (3-7%) of dietary fiber called beta-glucan. The beta-glucans have been approved in many countries as health benefitting soluble fiber due to its role in lowering postprandial blood glucose and the risk of cardiovascular diseases by reducing LDL cholesterol content [38].

The low incidence of hyperlipidemia and diabetes in the Tibetan population has been associated with the consumption of hull-less barley. The complex carbohydrates present in barley ensures slow release of glucose upon digestion into the bloodstreams thereby resulting in lowering glycemic index and thus is essential for patients suffering from diabetes [39].

The used of cereals in traditional health care systems has been in practices from centuries ago and numerous cultures throughout the globe still rely on these traditional cereal based formulations for their primary health care. Owing to recent advances done in plant sciences, there has been a tremendous increase in the use of these cereals and products derived from such cereals in both developing as well as developed countries for treatment of various ailments [40].

Extraction of Bioactive Compounds from Cereal Grains

Bioactive compounds  are gaining more popularity due to their antioxidant and medicinal properties. Due to which there is tremendous exploitation of bioactive compounds in formulation of different functional foods, chemical, nutraceuticals and pharmaceutical industries. The phenolics compound in cereals are mainly categorised into benzoic acid or cinnamic acid derivatives, while as ferulic acid has been found to be the major phenolic acid concentrated mostly in the outer layers of cereals [41]. The presence of these bioactive compounds like phenolics compound, tannins, and carotenoids in cereals contributed in antioxidant activities of cereals by different mechanisms [42]. Keeping into consideration the presence of phytochemicals and their antioxidant activities, different solvent like distilled water, ethanol, methanol and, acetone have been used for the extraction of these bioactive compounds. The extractions done by these solvents are evaluated in terms of total phenolic compounds, total flavonoids content, total anthocyanin/carotenoid contents and antioxidant properties. Free phenolic lavorr are present mainly in the outer layers of the pericarp while as bound phenolic acids are ester-linked to cell walls that requires an acid, base or enzymatic hydrolysis for extraction with solvent [43]. The application of different solvent mixtures such as methanol/water, ethanol/water and acetone/water have been found to enhanced the extraction rate and results in higher extraction yields of free phenols than pressurized liquid extraction methods as validated by Bonoli, et al. [44]. The extraction efficiency of any organic solvent used in extraction of bioactive compounds depends on the polarity of certain phenolic compounds. Thus the dilution of solvents generates a medium polarity facilitating extraction of other components that are not soluble in organic solvents [45]. The variations in the total phenolic contents of as extracted by using different solvent concentrations could be attributed to polarities of different compounds present in the selected cereals. The aqueous solvents had been found to be suitable for extracting some bioactive compounds with strong polarity. Acetone plus water solvent was found the best solvent for extraction of polyphenols with a broad range of polarity. The alcohols ethanol or methanol leads to development of hydrogen bonds between hydroxyl groups and oxygen atoms of the compounds, thereby contributing to more extraction efficiency than acetone [46]. The addition of water to organic solvent increases its polarity and thus enhancing the ability of extracting low, medium and high polarity compounds that represents a higher concentration of total flavonoids. Due to varied polarities of acetone (0.355), ethanol (0.654) and methanol (0.762), the extraction of different components varied depending on the polarity degree of the compounds. Thus no single solvent is capable of extracting simultaneously all classes of phenolic compounds from any cereal or by products. The tendency of solubility have been found to be associated with the stereochemistry of the phenols (polar and the nonpolar fractions) and the intermolecular hydrogen bonding forces between the phenolic compounds and the solvents.  A number of sensitive and selective analytical techniques have been developed for the determination and characterization of the bioactive compounds. Among which spectrophotometric, chromatographic, fluorometric, enzymatic, and electrophoretic methods are considered best ones.

Conclusion

Cereals are consumed as a whole or as an ingredient in different formulation of food choices. The nutritional elements in addition of chemical components that are present in small quantities usually in bran and germ part of cereal grains are called as bioactive compounds. The proteins of millets are gluten free and are non-allergenic, hence their consumption decreases triglycerides and C- reactive proteins that may prove beneficial in preventing cardiovascular disease. Sorghum is beneficial for diabetic patients than other cereals as its starches and sugars are released more slowly in human body and thus are having lower glycemic index. The extraction efficiency of any organic solvent used in extraction of bioactive compounds depends on the polarity of certain phenolic compounds. Thus the dilution of solvents generates a medium polarity facilitating extraction of other components that are not soluble in organic solvents.