Nutritional and functional roles of millets-A review

J Food Biochem. 2019;43:e12859. wileyonlinelibrary.com/journal/jfbc  

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© 2019 Wiley Periodicals, Inc.

1 | INTRODUCTION

In recent years, there has been a growing public interest for food not solely for their nutritional role but also for their functional roles geared toward preventing diseases rather than curative treatments. Cereal foods, a rich collection of essential macro and micro elements and with non‐nutrient bioactives/secondary metabolites/phyto‐ chemicals are important in the food system. Millets, which are rich

in minerals and vitamins with low fat, dietary energy, and glycemic index values, have been observed to numerous documented health benefits. Epidemiological evidences showed a close association of millets with a decrease in the incidence/risk factors of cardiovas‐ cular disease, diabetes, and certain cancers, etc. (Gong et al., 2018; Radhika et al., 2011; Singh & Raghuvanshi, 2012).

Currently, worldwide cereals consumption is increasing and it is used as a principal food source. However, there is a great demand for conventional/major tropical cereals like rice, wheat, maize, corn, and dhal, etc., though they have good trade in local and export markets.

Received: 13 December 2018 

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R E V I E W

Nutritional and functional roles of millets—A review

Srinivasan Nithiyanantham

 | Palanisamy Kalaiselvi

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Mohamad Fawzi Mahomoodally

 | Gokhan Zengin

 | Arumugam Abirami

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Gopalakrishnan Srinivasan

Srinivasan Nithiyanantham and Gokhan Zengin were contributed equally to this paper.

1_{Environment‐Omics‐Disease Research}

Center, China Medical University Hospital, China Medical University, Taichung, Taiwan

2_{Graduate Institute of Clinical Medical}

Sciences, China Medical University, Taichung, Taiwan

3_{Faculty of Science, Department of Health}

Sciences, University of Mauritius, Réduit, Mauritius

4_{Science Faculty, Department of}

Biology, Selcuk University, Konya, Turkey

5_{Department of Environmental}

Sciences, Bharathiar University, Coimbatore, India

Correspondence

Srinivasan Nithiyanantham, Environment‐ Omics‐Disease Research Center, China Medical University Hospital, China Medical University, Taichung, Taiwan.

Email: micronithibionithi@yahoo.co.in Gokhan Zengin, Science Faculty, Department of Biology, Selcuk University, Campus, Konya 42075, Turkey.

Email: gokhanzengin@selcuk.edu.tr [Correction added on 26 April 2019, after first online publication: the corresponding address of Srinivasan Nithiyanantham has been corrected.]

Abstract

The available cultivable plant‐based food resources in developing tropical countries are inadequate to supply proteins for both human and animals. Such limition of avail‐ able plant food sources are due to shrinking of agricultural land, rapid urbanization, climate change, and tough competition between food and feed industries for existing food and feed crops. However, the cheapest food materials are those that are derived from plant sources which although they occur in abundance in nature, are still un‐ derutilized. At this juncture, identification, evaluation, and introduction of underex‐ ploited millet crops, including crops of tribal utility which are generally rich in protein is one of the long‐term viable solutions for a sustainable supply of food and feed materials. In view of the above, the present review endeavors to highlight the nutri‐ tional and functional potential of underexploited millet crops.

Practical applications

Millets are an important food crop at a global level with a significant economic impact on developing countries. Millets have advantageous characteristics as they are drought and pest‐resistance grains. Millets are considered as high‐energy yielding nourishing foods which help in addressing malnutrition. Millet‐based foods are con‐ sidered as potential prebiotic and probiotics with prospective health benefits. Grains of these millet species are widely consumed as a source of traditional medicines and important food to preserve health.

K E Y W O R D S

Moreover, economic constrains making them non‐affordable for day to day life by local/rural peoples. On the other hand, a category of millet crops called “underutilized/neglected” have plenty of hidden potential in occupying the niches of local ecology, production, and consumption systems. They remain inadequately characterized and neglected by research despite their practical use. Exploration of such underutilized/neglected species provides sustainability, preserva‐ tion, and diversification of the ecosystem, economic empowerment of rural peoples and nutritional and health security, a greater de‐ mand by the world today (Gopalan, Rama Sastri, & Balasubramanian, 2009; McDonough, Rooney, & Saldivar, 2000).

Millets are an important food crop on a global level with a signifi‐ cant economic impact on developing countries. Millets have advanta‐ geous characteristics as they are drought and pest‐resistance grains. They are small‐ to medium‐size crops that are cultivated throughout the tropics and subtropical region. The genus millets belonging to

Poaceae (true grass) comprises major and minor millets which are dis‐

tributed in India, China, Malaysia, Srilanka, and Australia. The Poaceae family plays a vital function in both farming and environmental nour‐ ishment (Wang, Jiang, Jing, Wang, & Zhang, 2010). The major types are Pearl millet (Pennisetum glaucum, with synonyms of P. americanum,

P. typhoides, and P. typhoideum), Foxtail millet (Setaria italica), Proso

millet or white millet (Panicum miliaceum), and Finger Millet (Eleusine

coracana). Minor millets includes Barnyard millet (Echinochloa spp.),

Kodo millet (Paspalum scrobiculatum), Little millet (Panicum sumatrense), Guinea millet (Brachiaria deflexa/Urochloa deflexa), and Browntop mil‐ let (Urochloa ramose/Brachiaria ramose/Panicum ramosum) (Chinchole, Pathak, Singh, & Kumar, 2017; ICRISAT, 2017; Yang et al., 2012).

Millets are considered as high‐energy yielding nourishing foods which help in addressing malnutrition. They are consumed as flour, rolled into balls, parboiled, and served as porridge with milk (FAO, 2009). According to the FAO, the traditional food processing meth‐ ods, such as decortications, milling, germination, fermentation, malt‐ ing, and roasting of millets are recommended in order to prevent their antinutritional properties and improve their edible qualities. Functional properties, such as water and oil holding capacity, vis‐ cosity, foaming activity, bulk density, and swelling power of millets are the fundamental physicochemical properties that reveal the in‐ tricate relations between the structure, molecular components and composition and physicochemical properties of food components (Ramashia, Gwata, Meddows‐Taylor, Anyasi, & Jideani, 2017). Table 1 shows the content of proximate composition of different varieties of millets. Millets could be processed and consumed as traditional local

foods, such as popping meals, porridges, chapati, dosa, pastas, bread, and biscuits (Adebiyi, Obadina, Adebo, & Kayitesi, 2017; Jalgaonkar & Jha, 2016; Omoba, Taylor, & Kock, 2015). Millet based foods and beverages are eaten as a major diet in most of the African countries (Amadou, Mahamadou, & Le, 2011). Due to the presence of natu‐ ral bioactive compounds, such as richness in calcium, dietary fiber, polyphenols, and protein in the millet crops which have a number of health benefits (Amadou, Gounga, & Le, 2013; Annor, Tyl, Marcone, Ragaee, & Marti, 2017; Izadi, Nasirpour, Izadi, & Izadi, 2012; Srikanth & Chen, 2016). Millets are rich in amino acids, especially sulfur con‐ taining amino acids (methionine and cysteine); and also superior in fatty acids than maize, rice, and sorghum (Jideani, 2012; Obilana & Manyasa, 2002). In general, millets are limited in lysine and tryp‐ tophan content and vary with cultivar. However, most cereals con‐ tain the essential amino acids as well as vitamins and minerals (Devi, Vijayabharathi, Sathyabama, Malleshi, & Priyadarisini, 2011; FAO, 2009; Gull, Kmalesh, & Kumar, 2015).

Millet based foods are considered as potential prebiotic and pro‐ biotics with prospective health benefits (Banerjee, Sanjay, Chethan, & Malleshi, 2012; Palaniswamy & Govindaswamy, 2016). Millet grains are widely consumed as a source of traditional medicines and are important food to preserve health. The phytonutrients and vitamins may be responsible for the antioxidant, anticancer and anti‐inflam‐ matory, antifungal, and blood clot inhibition properties of millet crops (Dykes & Rooney, 2007; Yadav, Chaudhary, Singh, & Gupta, 2013).

Given that several studies have been conducted on the nutri‐ tional and biological roles of millets, this review attempts to present a single compilation that deals with the origin and distribution, brief morphological characters, indigenous knowledge, chemical compo‐ sition, and results of reported research finding on the nutritional properties of millet grains.

2 | ORIGIN, DISTRIBUTION, AND

MORPHOLOGY

Millets are small grained cereal crops, such as Kodo, Foxtail, Proso, Little, and Barnyard, which are widely distributed and cultivated worldwide as a staple food. Millets probably grow in the Asian and African countries and parts of Europe but are cultivated through‐ out the tropical and subtropical regions of the world (Saleh, Zhang, Chen, & Shen, 2013). Millets are considered as the first domesti‐ cated cereals and characterized by their remarkable facility to

Millet varieties Moisture Ash Protein Carbohydrates Fat

Total dietary fiber Finger millet 13.1 2.7 7.7 83.3 1.5 11.5 Pearl millet 12.4 1.64 11.6 59.8 5 11.3 Foxtail millet 11.2 0.47 12.3 75.2 4.3 2.4 Proso millet 11.9 NA 12.5 80.1 1.1 – Note. Gopalan, Ramashastri, and Balasubramanium (2004), USDA National Nutrient Database (2016). TA B L E 1   Proximate composition of

varieties of millet grains (g/100 g, dry basis)

survive in less fertile soil, drought resistance, pest resistance, and short growing season usually 45–60 days (Awika, 2011). As of now, millets are highly consumed as a staple food by millions of poor peo‐ ple in Africa and Asia. With regard to production of millets, India oc‐ cupies a significant position in world productivity and marketability. For a long time, millet crops were valued by man because of their nutritional and edible qualities (Bukhari, Ayub, Ahmad, Mubeen, & Waqas, 2011). Though millets seem small‐seeded cereals but contain a number of dietary advantages (Dayakar, Bhaskarachary, Arlene Christina, Sudha Devi, & Tonapi, 2017).

P. glaucum (Pearl millet) is the drought resistant crop and majorly

cultivated as a staple food and feed at sub‐Saharan Africa and India (Amadou et al., 2011; Obiana, 2003). India is the largest producer of pearl millet (Bhattacharjee, Khairwal, Bramel, & Reddy, 2007). The seeds are 3–4 mm long and 2.25 mm wide, usually yellowish‐gray in color (Hannaway & Larson, 2004). Eleusine coracona (Finger millet also known as Small millet) is a salt tolerant plant and considered as an important cereal after maize and it is widely grown in east and central Africa, India and Uganda (Satish et al., 2016). Their grains are very small and vary in size up to 2 mm in diameter and dark brown and red brown in color. S. italica (Foxtail millet) is also the drought and high salt tolerating crop adapted to arid and semi‐arid areas and mainly grown in China as a food and feed source (Krishnamurthy et al., 2014; Pant, Irigoyen, Doust, Scholthof, & Mandadi, 2016). Seeds are 2–3 mm size and light cream in color. P. miliaceum (Proso mil‐ let is considered as the largest millet crop) cultivated in the Pacific Northwest USA, Northern China, Eastern Asia, Mongolia, Manchuria, Japan, India, Eastern and Central Russia (Zhang et al., 2016). They are a drought resistant and high temperature tolerant crop and seed weight from 5 to 9 mg (Habiyaremye et al., 2017). Paspalum

scorbiculatum (Kodo millet) is drought resistant, grown on poor soils

and it is widely distributed in arid and semi‐arid regions of India and African countries (Kannan, Thooyavathy, Kariyapa, Subramanian, & Vijayalakshmi, 2013). It is a monocot crop and smaller size seeds, 1.5 mm in width, 2 mm in length and light brown to dark gray in color. Echinochlo frumentacea (Barnyard millet) is the fastest grow‐ ing crop under unfavorable conditions and it is commonly cultivated in Egypt (Farrell, 2011). Panicum miliare (Little millet) is cultivated throughout India. These plants are generally shorter and are grown in sandy loam, slight acidic and saline nature of soil.

3 | TR ADITIONAL USES OF MILLET

Millet grains are important as food for poor families to battle mal‐ nutrition and a chief source of income. In traditional systems, indig‐ enous knowledge plays a central role in disease diagnosis and health care practices. Celiac disorder is an immune‐mediated enteropathy which is triggered by intake of gluten rich food (Becker, Damiani, Melo, Borges, & de Barros Vilas Boas, 2014). Millets are gluten‐free food and can be a substitute for celiac diseases and gluten sensitive patients (Annor, Marcone, Corredig, Bertoft, & Seetharaman, 2015; Saleh et al., 2013). Polyphenols of millets exhibit inhibitory activity

against its malt amylase, aldose reductase of cataract eye lenses and snake venom phospholipases (Mathanghi & Sudha, 2012). Phenolics of finger millet seed coat were reported to decrease hyperglyce‐ mia by blocking the α‐amylase and α‐glucosidase enzyme activity (Shobana, Sreerama, & Malleshi, 2009). Seed coat phenolics of finger millet are also reported as an inhibitor of cataractogenesis in human eye lenses (Chethan, 2008). Food processing techniques, such as soaking, germination, fermentation, and puffing of millets enhance the nutritional quality of millets, improve digestibility with reducing antinutrient content in their cereals (Handa, Kumar, Panghal, Suri, & Kaur, 2017; Jaybhaye & Srivastav, 2015). The presence of antinutri‐ ent in finger millet was reported to lower glycemic effect, reduced starch digestibility, and absorption (Kumari & Sumathi, 2002). Pearl millets were traditionally consumed for the treatment of celiac dis‐ order, constipation and several noncommunicable diseases (Jnawali, Kumar, & Tanwar, 2016). In China, foxtail millet is highly appreci‐ ated for its high nutritional value, easily digestible and non‐aller‐ gic properties and also it plays a significant role in human health. The fermented products of millets are consumed as probiotics and recommended for the treatment of diarrhea in young children (Manisseri & Gudipati, 2012; Nduti et al., 2016).

4 | NUTRITIONAL VALUES

Millet crops have long been valued as part of a nourishing diet. It is well‐established that millet diets are a rich source of phytocon‐ stituents, vitamins, minerals, and fibrous materials (non starch polysaccharides) that are essential for normal growth, control type 2 diabetes and overall nutritional well‐being (Habiyaremye et al., 2017; Schoenlechner, Szatmari, Bagdi, & Tomoskozi, 2013). A num‐ ber of health benefits are associated with the consumption of mil‐ lets, largely due to the bioactive phytochemicals found in these cereals, such as lignans, flavonoids, phenolics, beta‐glucan, ster‐ ols, inulin, pigments, dietary fiber, and phytate (Amir et al., 2014; Kamara, Zhou, Zhu, Amadou, & Tarawalie, 2009; Narasinga, 2003). The common health benefits of some of millet varieties are shown in Table 2. Those nutraceuticals are reported to be important in the management and/or treatment of asthma, migraine, blood pressure, diabetes, cardiovascular diseases, and for the immune system (Anju & Sarita, 2010; Balasubramanian, Vishwanathan, & Sharma, 2007; Gupta et al., 2017). Millet‐based foods are described to be prospec‐ tive prebiotics and probiotics with major health benefits (Lei, Friis, & Michaelsen, 2006). Phenolics rich millets are of great significance in health, aging, and metabolic syndrome (Hegde, Rajasekaran, & Chandra, 2004). The presence of phytate in the millets are allied with anticancer and cholesterol lowering property (Coulibaly, Kouakou, & Chen, 2011). Millets with fiber‐rich content are essential for prevent‐ ing the gall stone formation. Millets are most commonly thought of as a good source of proteins which play a crucial role in the suppres‐ sion of malnutrition (Chandel, Kumar, Dubey, & Kumar, 2014; Prasad, 2010). Natural foods, especially millet crops, play a major role in human nutrition as excellent sources of antioxidants, and contain a

variety of proteins, vitamins, and mineral substances (nutritive value of 100gm of various millet crops are shown in Table 3).

Millets and their food products contain biologically active com‐ pounds which possess antioxidant potential (Izadi et al., 2012). They are essential components and hence used as a functional food (Devi et al., 2011). Millet grain nutrients, vitamins, and flavonoids help to prevent unwanted damage to cell membranes and other structures of the body by neutralizing free radicals. Antioxidants in millet grains have been documented to possess antitumor activity. The consump‐ tion of millet grains may significantly improve bone quality due to the presence of vitamin content and its bioactive compounds which preserve bone calcium concentration and increase antioxidant sta‐ tus (Chethan & Malleshi, 2007; Devi et al., 2011).

5 | PHY TOCHEMICAL COMPOSITION OF

MILLETS

5.1 | Phenolics and flavonoids

Phenolic compounds are aromatic secondary metabolites of plants which play a significant role in color (gray, yellow, green, and creamy white color) sensory and nutritional qualities and antioxidant prop‐ erties of food (Reichert, 1979). They are naturally present in millets and plant sources. These compounds are a part of the everyday diet and also used as medicines or supplements. Phenolic compounds, such as phenolic acids, flavonoids, stilbenes, tannins, and lignans can scavenge free radicals and quench ROS, and therefore provide

effective means for preventing and treating free radical‐medi‐ ated diseases (Subba Rao & Muralikrishna, 2002). Polyphenols are capable of removing free radicals, chelate metal catalyst, activate antioxidant enzymes, reduce α‐tocopherol radicals, and inhibit oxi‐ dases (Singh & Raghuvanshi, 2012). Phenolics substances like flavo‐ noids and phenolic acids in food behave as natural antioxidants and therapeutic medicine due to their nutraceutical and health benefits (Siddhuraju & Becker, 2007). Millets are known for their rich sources of bioactive compounds, including vitamin, phenolics, and flavo‐ noids and their glucosides, folic acid, carotenoids, coumarins, highly fermentable fiber, and potassium with potential health‐promoting properties (Viswanath, Urooj, & Malleshi, 2009). These bioactive compounds are known to act as free radical‐scavengers, to modu‐ late enzymatic activities and to protect against a variety of diseases, particularly cardiovascular diseases and also some types of cancer (Chandrasekara & Shahidi, 2011). Millets grains are good sources of polyphenols (Chethan, 2008). Table 4 shows the total phenolic con‐ tent of soluble and bound phenolic extracts of some common mil‐ lets (Chandrasekara & Shahidi, 2011) Gallic acid, polymeric tannins, protocatechuic acid, gentisic acid, caffeic acid, vanillic acid, syringic acid, ferulic acid, para coumaric acid, transcinnamic acid, and 5‐n‐ alkylresorcinols are the major groups of phenolic compounds pre‐ sent in all types of millet grains (Bellato, Ciccoritti, Frate, Sgrulletta, & Carbone, 2013; Pradeep & Guha, 2011; Pradeep & Sreerama, 2017; Shobana et al., 2009; Siwela, Taylor, Milliano, & Dudu, 2010). Millet polyphenols are reported to possess bioactivities, such as free radical scavenging, anticancer, antimicrobial, and anti‐oesteogenic

Name of

the millets Major health benefits References

Pearl millet Prevent heart related disease, lower the level of triglycerides, act as natural source of antioxidants, reduce the incidences of inflamma‐ tory bowel diseases

Chandrasekara and Shahidi (2011), Islam, Manna, and Reddy (2015), Kim and Je, (2016), Liu, Wu, Li, and Zhng (2015)

Finger

millet Reducing the risks of diabetes mellitus and gastro‐intestinal tract disorders, ability to scavenge the free radicals Muthamilarasan, Dhaka, Yadav, and Prasad (2016) Barnyard millet Act as inhibitor of the cancer developing cells, reducing blood glucose, and lipid levels

Sharma, Saxena, and Riar (2016), Ugare, Chimmad, Naik, Bharati, and Itagi (2011)

Proso millet

It improve the glycemic responses and plasma level, protect against D‐galactosamine‐induced liver injury

Park et al. (2008), Ito et al. (2008)

Little millet Reduce cholesterol level in the case of cardiovascular disorder, reduce fasting blood glucose, blood glucose, and lipid parameters in diabetic subjects

Surekha (2004)

Foxtail millet

Act as anti‐hyperglycemic and anti‐lipidemic agents in diabetic conditions, inhibits pro‐inflamma‐ tory and hypertrophic response

Sireesh et al. (2011), Choi et al. (2005)

(Chandrasekara & Shahidi, 2011; Nambiar, Dhaduk, Sareen, Shahu, & Desai, 2011).

Flavonoids are the main class of polyphenols, the basic chemical structure which contains a heterocyclic C6‐C3‐C6 skeleton (Hwang, Shih, & Yen, 2012). Many plants are considered to be excellent sources of flavonoids that could be used to contribute to a healthy diet along with food preservatives. Flavonoids are prominent com‐ ponent of millets. Dietary flavonoids are considered to be even more powerful antioxidants than vitamins C and E (Sokol‐Letowska, Osmianski, & Wojdylo, 2006). The commonly found flavonoids in millets are catechin, quercetin, luteolin, orientin, apigenin, isoorien‐ tin, vitexin, myricetin, isovitexin, daidzein, sponarin, violanthin, lu‐ cenin‐1, and tricin (Chandrasekara & Shahidi, 2011; Pathak, Gupta, Shukla, & Baunthiyal, 2018; Pradeep & Sreerama, 2017). Millets flavonoids have shown a wide range of therapeutic properties for medical and clinical applications, such as anti‐inflammatory, antihy‐ pertensive, diuretic, analgesic, anticancer, and hypolipidemic effects (Banerjee et al., 2012; Chethan, 2008; Edge, Jones, & Marquart, 2005; Ekta & Sarita, 2016).

5.2 | Dietary fiber

Fibers are part of the plant food and not of meat. It is a less essential nutrient, but important as an element for internal maintenance. Fiber

is a non absorbable complex carbohydrate that comes from the cell walls of plants. There are two types of fiber that vary in dietary func‐ tions; the soluble and in‐ soluble fibers. Fiber is not broken down chemically in the body but aids digestion, lower cholesterol, and low calorie food with no animal fat (Ahuja, Nath, & Swamy, 2010). A good amount of research has revealed the relationship between DF intake and the incidence of constipation, obesity, cardiovascular diseases, colon cancer, and diabetes mellitus (Balasubramanian, 2013). The fiber can be used for technological purposes, such as a bulking agent or fat substitute along with nutritional purposes. The physiological actions of DF are likely based on its physicochemical properties, such as water‐ and oil‐holding capacities, absorption of organic molecules, bacterial degradation, cation‐exchange capacity, and antioxidant ac‐ tivity (Lestienne, Buisson, Lullien‐Pellerin, Picq, & Trèche, 2007).

Millet seed coat contains pectin, cellulose, and hemicelluloses which are resistant to breakdown by digestive enzymes, and there‐ fore are sources of dietary fiber (Chethan & Malleshi, 2007). The presence of dietary fiber in seed coat of millet grains are beneficial to human health which affects several metabolic and digestive pro‐ cesses, such as effects on glucose absorption and cholesterol lev‐ els (Upadhyaya et al., 2011). Seed coat matter contains high fiber content which can be used as a good source of dietary fiber and it produces an important quantity of by‐products, which are mainly used as composite flour in biscuit preparation (Rateesh, Usha,

Name of the millet cereals

For 100 g of each cereal

Proteins (g) Fiber (g) Minerals (g) Iron (mg) Calcium (mg)

Pearl millet 10.6–14 1.3–2.5 2–2.3 7.5–16.9 10–38 Finger millet 7.3–10 3.6–4.2 2.7–3 3.9–7.5 240–410 Foxtail millet 12.3–15 4.5–8.0 2–3.3 2.8–19 10–31 Proso millet 10–13 2.2–9 1.9–4 0.8–5.2 14–23 Kodo millet 8.3–10 5–9.0 2.6–5 0.5–3.6 10–31 Little millet 7.7–15 4–7.6 1.5–5 9.3–20 17–30 Barnyard millet 6–13 10.1–14 4–4.4 15.2 11 Rice 6.8 0.2 0.6 0.7 10 Wheat 11.8 1.2 1.5 5.3 41 Note. Millet network of India (http://milletindia.org); Himanshu, Chauhan, Sonawane, and Arya (2018). TA B L E 3   Nutritional profile

TA B L E 4   Total phenolic content of soluble and bound phenolic extracts of some common millets

Millet variety

Soluble phenolic content (µmol of ferulic acid equiv/g of defatted meal)

Bound phenolic content (µmol of ferulic acid equiv/g of defatted meal)

Finger millet 31.39 ± 1.22 3.20 ± 0.19 Pearl millet 8.63 ± 0.38 9.4 ± 0.17 Proso millet 7.19 ± 0.12 2.21 ± 0.01 Foxtail millet 10.79 ± 0.82 11.59 ± 0.23 Kodo millet 32.39 ± 0.93 81.64 ± 0.15 Little millet 12.67 ± 0.33 9.14 ± 0.17

Manohar, & Malleshi, 2011; Rateesh, Ushakumari, Sai Manohar, & Malleshi, 2008).

6 | PHARMACOLOGICAL ROLES OF

MILLETS

Research in millet grains has made significant advances in recent years. Millets have been shown to produce a variety of compounds and it possesses biological activity of potential pharmaceutical value. Over the past decades, the isolated compounds and crude extracts from various millet grains have generated an enormous amount of interest in the pharmaceutical industry. This review will cover areas related to antimicrobial, anti‐inflammatory, antidiabetic, anticancer, and antioxidant activity of varieties of millets that can be supported through science and claims substantiation.

6.1 | Antimicrobial and anti‐inflammatory activity

Millet grains have various secondary metabolites which show a wide spectrum of biological properties. The bioactive secondary metabo‐ lites of millet varieties, such as phenolics and flavonoid compounds exhibit the antibacterial and antifungal activities (Xu et al., 2011). Radhajeyalakshmi et al. (2003) reported the higher antifungal activ‐ ity of protein extract of pearl millet millets than the other varieties of millets against phytopthogenic fungi, such as Rhizoctonia solani,

Macrophomina phaseolina, and Fusarium oxysporum. Banerjee et al.

(2012) reported the role of phenolic and flavonoid compounds of finger millets against the inhibitory activity of proliferation of bacte‐ rial pathogens, such as Escherichia coli, Bacillus cereus, Listeria mono‐

cytogenes, Staphylococcus aureus, Streptococcus pyogenes, Serratia marcescens, Proteus mirabilis, Pseudomonas aeruginosa, Klebsiella pneumonia, and Yersinia enterocolitica.

Antimicrobial activities of phenolic compounds of finger millet grains may be used as a potent pharmaceutical alternative for the treatment of various bacterial and fungal infections (Viswanath et al., 2009). Siwela et al. (2010) examined the mechanism of loss of fungal functionality on seed coat phenolic extract of finger millet. According to these, phenolic extracts of finger millets play a role as free radicals for oxidation of microbial membranes and cell compo‐ nents of fungi and phenolic compounds and inactivate the enzymatic activity of fungal proteins. Very few researchers have examined the anti‐inflammatory potential of millet grains as drugs in the pharma‐ ceutical field. Millets, especially finger millet have extensively been studied as a rich source of bioactive compounds and examined on the dermal wound healing process in diabetes induced rats with ox‐ idative stress‐mediated modulation of inflammation (Rajasekaran, Nithya, Rose, & Chandra, 2004).

6.2 | Antidiabetic activity

Bioactive compounds of millet varieties possess antidiabetic effects due to their ability to inhibit the major digestive enzymes of clinical

relevance, namely α‐amylase and α‐glucosidase (Kumari & Sumathi, 2002). They were examined for the antinutritional factors of finger millet based diet for reduce starch digestibility and absorption which cause lower glycemic effect. The active biomolecule from these grains have antidiabetic potential through modulation of glucose‐induced oxidative stress and inhibition of starch‐digestive enzymes. Protein concentrate of Korean foxtail millet and proso millet improved the glycemic responses and are reported to significantly decrease insu‐ lin level and increase plasma diponectin and HDL cholesterol levels relative to casein diet in type 2 diebetic mice (Choi et al., 2005; Park, Ito, Nagasawa, Choi, & Nishizawa, 2008). Ito, Ozasa, Noda, Arii, and Horikawa (2008) confirmed the protective effect of protein concen‐ trate from Proso millet against D‐galactosamin‐induced liver injury in rats. Aqueous extract of S. italica (Foxtail millet) seeds showed anti‐ hyperglycemic and anti‐lipidemic activities against streptozotocin‐ induced diabetic rats (Sireesha, Kasetti, Nabi, Swapna, & Apparao, 2011). S. italica seeds could possibly decrease the levels of triglyc‐ erides, total LDL (low‐density lipoproteins), VLDL (very low‐density lipoproteins) cholesterol and increase HDL (high‐density lipoproteins) cholesterol in diabetic treated rats compared to those in diabetic un‐ treated rats. Lee, Chung, Cha, and Park (2010) examined the anti‐hy‐ perlipidemic activity of Foxtail millet consumption on hyperlipidemic rats and found a decreased level of triglycerides. Shobana, Sreerama and Malleshi (2009) proved the hypoglycemic, hypocholesterolemic, nephroprotective, and anti‐cataractogenic activity of finger millet against diabetes induced rats. Jain et al. (2010) confirmed the signifi‐ cant antidiabetic activity of aqueous and ethanolic extract of Kodo millet (P. scrobiculatum) against alloxan induced diabetic rats.

6.3 | Antioxidant activity

Phenolics and flavonoids are present in millet grains having the ability to serve as antioxidants by chelating metal ions, protective agents against free radical induced cell damage, preventing radical formation, and improving the antioxidant endogenous system (Miller, 2001). The significant antioxidant activity of different millet grains

viz,. Kodo millet, Finger millet, Little millet, Foxtail millet, Barnyard

millet, Great millet, and their white varieties were reported in terms of DPPH reduction capacity as well as the Ferric reducing antioxi‐ dant potential (Devi et al., 2011; Kamara, Amadou, & Zhou, 2012; Quesada et al., 2011). Antioxidant potential and phenolic content of millet grains may serve as an anti‐aging agent and protect the cells against metabolic syndrome (Hegde et al., 2004). Viswanath et al. (2009) studied the antioxidant activity of finger millet and confirmed the free radical scavenging potential of the phenolic content of seed coat. Bellato et al. (2013) proposed the regular intake of whole grain could protect the body against several types of chronic disorders due to the presence of antioxidant compounds, such as phenolics and flavonoids. Chandrasekara and Shahidi (2011) studied the an‐ tioxidant potential, such as total phenolic content, total flavonoid content, ferrous ion chelating activity, and singlet oxygen scavenging capacity of seven millet varieties and confirmed that the phenolic extracts of millets showed anticancer activity by scavenging peroxyl

and hydroxyl radicals. Pradeep and Guha (2011) examined the ef‐ fect of processing on the nutraceuticals and antioxidant activity of little millets (P. sumatrense) and reported that roasted samples nota‐ bly enhanced the neutraceutical properties in terms of increasing the phenolic content and also its free radical scavenging potential. Wei et al. (2018) studied the effect of high salt on hypertension and myo‐ cardial damage induced by millet enriched diet using animal models. They found that a millet enriched diet had significant effects on the reduction of blood pressure and concluded that anti‐oxidative stress effect of millets contributes to the protection of myocardial damage caused by HS intake.

7 | CONCLUSION

Since time immemorial, millets have been used traditionally as a ce‐ real and also an important and unique source of various types of bioactive compounds having diverse health functions. In this re‐ view, we have focused on the nutritional aspect of varieties of mil‐ lets along with their pharmaceutical potential. Millet grains can be used as easily accessible source of natural antioxidants to protect the body against various oxidative stresses. Among different fami‐ lies of antioxidants, phenolics, and flavonoids are most recurring fol‐ lowed by different minerals sources and vitamins. The most common use of millets were found to be in diseases, such as hypoglycemic and hypolipidemic. Other major application of these millet grains was in the form of anti‐inflammatory, antimicrobial, and antitumor. Considerable preclinical evidence has accumulated over the last 15 years, almost all of which indicates positive results for a range of test systems. Millet grain residues used as potential fiber sources in the enrichment of foods could permit the use of them in developing new natural ingredients for the food industry. A significant amount of studies have been done on the biological activity and possible ap‐ plication of these compounds, and hence extensive investigation on its pharmacodynamics, kinetics. Proper standardization and clinical trials are needed to exploit their therapeutic utility to combat vari‐ ous diseases, such as cataract, gastrointestinal disorders, and cardio protection.

CONFLIC TS OF INTEREST

The authors declared that they have no conflict of interest.

ORCID

Gokhan Zengin https://orcid.org/0000‐0001‐6548‐7823

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How to cite this article: Nithiyanantham S, Kalaiselvi P,

Mahomoodally MF, Zengin G, Abirami A, Srinivasan G. Nutritional and functional roles of millets—A review. J Food

Biochem. 2019;43:e12859. https://doi.org/10.1111/