Nutritional advantages of barnyard millet and opportunities for its processing as value-added foods

Abstract

Barnyard millet (Echinochloa species) has received appreciable attention for its susceptibility to biotic and abiotic stresses, multiple harvests in a year and rich in micronutrients, fibers and phytochemicals. It is believed that the consumption of barnyard millet can possess various health benefits against diabetes, cardiovascular diseases, obesity, skin problems, cancer and celiac disease. The flour of barnyard millet is gluten-free and can be incorporated into the diet of celiac and diabetic patients. Considering the nutritional value of millet, various millet-based food products like bread, snack, baby foods, millet wine, porridge, fast foods and millet nutrition powder can be prepared. Future research and developments on barnyard millet and its products may help cope with various diseases known to humans. This paper discusses barnyard millet's nutritional and health benefits as whole grain and its value-added products. The paper also provides insights into the processing of barnyard millet and its effect on the functional properties and, future uses of barnyard millet in the field food industry as ready-to-cook and ready-to-eat products as well as in industrial uses, acting as a potential future crop contributing to food and nutritional security.

Introduction

Nutritional food quality is a crucial factor in ensuring an individual's health and physical well-being (Sarita and Singh 2016). An extensive world population feeds upon cereal grains, a vital part of the consumer’s regular diet. Wheat, rice and maize are some of the most widely consumed grains consumed in whole or fractionated form (Rasane et al. 2015). Some grains have been primarily used for human consumption and secondarily for animal feed since the beginning of civilization (McKevith 2004). Millets are the small-seeded annual grass crops, grown in the different regions of the world, such as temperate, tropical and sub-tropical (Kajuna 2001). They contain all vital nutrients and their protein content is considered to be equal or superior to wheat (Triticum aestivum), rice (Oryza sativa), maize (Zea mays) grains (Kumar et al. 2018). Millets are a good source of proteins, dietary fibers, iron, zinc, calcium, phosphorus, potassium, vitamin B and constitute a range of vital amino acids than major cereals (Saleh et al. 2013). On the Hundred and Sixtieth Session of Food and Agriculture Organization (FAO) in the year 2018, the FAO council proposed to support the Government of India's plan to create the International Year of Millets in 2023 (FAO 2018) and UNGA adopted the proposal of declaring 2023 as the International Year of Millets (FAO 2022).

Barnyard millet (Echinochloa species) is an ancient millet crop cultivated in warm and temperate regions of the world. It is abundantly harvested in Asia, notably in India, China, Japan and Korea (Madhusudhana et al. 2018). Echinochloa esculenta and Echinochloa frumentacea are the two main species of Barnyard millet, billion-dollar grass is another name for Indian barnyard millet (Kaur and Sharma, 2020). Barnyard millet shows rapid growth and early maturity, which has attracted the attention of farmers in the United States and Japan as a fodder crop and it may provide up to eight harvests per year (Yabuno et al. 1987). Encouragement of millet cultivation can help to achieve the United Nations Sustainable Development Goal 2 (SDG2) for the attainment of ‘zero hunger' with the objective of "End hunger, achieve food security and improved nutrition and promote sustainable agriculture" as millets are often cultivated as rain-fed crops by utilizing less or no fertilizers (Ceasar and Maharajan 2022). The nutritional benefits of barnyard millet have attracted the attention of many worldwide researchers resulting in increased research and using barnyard millet as a food ingredient in several foods which will further help in achieving good health and well being (SDG3). The paper highlights the importance of barnyard millet as the crop of future to attain nutritional and food security.

Origin and taxonomy of barnyard millet

Barnyard millet is a member of the genus Echinochloa, the Poaceae family, and the Panicoideae subfamily and is a self-pollinating crop (Renganathan et al. 2020; Kumari et al. 2021). The Echinochloa genus contains approximately 250 annual and perennial species widely grown throughout agro-climatic regions (Bajwa et al. 2015). There are different Echinochloa species found in the world, some of the commonly known species are Echinochloa colona, also known as jungle rice originated in China and Japan, Echinochloa crusgalli, known as barnyard grass, originated from China, Japan and Korea, Echinochloa frumentacea which is also known as Indian barnyard millet and its origin is from the Asia including the countries like India, Pakistan and Nepal and Echinochloa esculenta also known as Japanese barnyard millet have been originated from Eastern Asia, China, Japan and Korea (Renganathan et al. 2020). Barnyard millet is an under-utilized Kharif crop that develops well in rainfed situations on slopes up to 2000 m above sea level (Kumari et al. 2021). It is widely grown in several countries, including Africa, Malaysia, the East Indies and the United States (Anuradha et al. 2014; Sood et al. 2015). In rice fields, E. crusgalli is known to be the fastest-growing weed (Kumari et al. 2021). The crop plant is a tall, robust, annual plant that reaches a height of 220 cm and the leaf blades are plain and broad, with no ligules (Sood et al. 2015). Japanese barnyard millet grows to a height of 50 to 100 cm, and its inflorescence consists of a panicle with up to 15 lateral branches (Kajuna 2001). The plant maintains the shortest generation period of any small millet, the quickest growth rate and achieves the life cycle from seed to seed in 45–60 days (Sood et al. 2015).

Consumption and production of barnyard millet as Nutri-cereal

Millets were the first cereal grain to be used for domestic purposes and are recognized as one of the earliest foods known to humans, as per the records of the International Crop Research Institute for the Semi-Arid Tropics (ICRISAT), approximately 90 million people in Asia and Africa consume millets as a staple meal, whereas 500 million people in more than 30 nations rely on sorghum. However, these traditional crops have mostly been ignored during the last 50 years, due to crops including maize, wheat, rice and soybeans (FAO 2018). As mentioned by FAO (2022), in 2019 the total area utilized for millet production was about 718 lakh ha with a production rate of 863 lakh tons, led by Africa in the area of 489 lakh ha and production of about 423 lakh tons, followed by America, Asia, Europe, Australia and New Zealand (Ministry of Agriculture & Farmers Welfare, 2022). Barnyard millet is the world's fourth-largest cultivated minor millet, providing food security to people worldwide (Madhusudhana et al. 2018). In terms of area (0.146 m/ha) and production (0.147 MT), India is the largest producer of barnyard millet, with average productivity of 1034 kg/ha during last three years (Madhusudhana et al. 2018).

Nutrient composition of barnyard millet

Barnyard millet is classified as a minor cereal crop providing higher nutrients than other cereals (Shanmugapriya and Nazni 2020). It provides ample nutrients and is a healthy grain (Veena Bharati et al. 2005) which is high in protein, fiber, fat, vitamins and minerals such as iron, zinc, calcium, magnesium and essential amino acids (Chandel et al. 2014; Singh et al. 2022). It is rich in essential fatty acids like linoleic acid, palmitic acid and oleic acid as well as minerals like iron, calcium and magnesium, where magnesium and niacin (B₃) help to lower cholesterol levels and phosphorus minerals, improve the metabolic process and food conversion into energy (Veena Bharati et al. 2005). The approximate composition of barnyard millet is presented in Table 1, proximate composition /100 gm is 10.5% protein, 3.6–3.8% fat, 51.5–62 g/100gm carbohydrate, 398 kcal/100 g energy, 5.41–6.8% crude fiber and the total dietary fibre content is found to be high of about 12.6% including soluble (4.2%) and insoluble (8.4%) dietary fibre (Ugare et al. 2014; Singh et al. 2022).

Table 1.

Nutritional composition of barnyard millet grain

Nutritional composition	Compounds	Content	References
Moisture		8.7%	Ugare et al. (2014)
Calorific value		398.0 (kcal/100 g)	Ugare et al. (2014)
Protein		10.5%	Ugare et al. (2014)
Crude protein	Albumin Globulins Prolamins Glutelins	11.3–17.2 (%) 11.3–17.2 (%) 14.3–20.9 (%) 45.2–63.5 (%	Renganathan et al. (2020)
Fat	Crude fat	3.6–3.8 (%)	Ugare et al. (2014)
Starch	Carbohydrate	51.5–62 (g/100gm)	Saleh et al. (2013)
	Amylose	20.0 (%)	Renganathan et al. (2020)
Ash		4.7–5.0 (g/100 g)	Renganathan et al. (2020)
Minerals	Total mineral content Calcium Copper Iron Magnesium Manganese Phosphorus Potassium Sodium Zinc	2.7–4.2% 17.1–32.7 (mg/100 g) 0.6 (mg/100 g) 15.6–18.6 (mg/100 g) 18.6 (mg/100 g) 0.7 (mg/100 g) 281(mg/100 g) 29 8 (mg/100 g) 13–20 (mg/100 g) 4.9 (mg/100 g)	Shinde et al. (2021) Veena Bharati et al. (2005) Renganathan et al. (2020) Saleh et al. (2013) Renganathan et al. (2020) Renganathan et al. (2020) Nazni et al. (2016) Renganathan et al. (2020)
Fiber	Crude fiber Total dietary Fiber Insoluble Dietary Fiber Soluble dietary fiber	5.41–6.87 (%) 12.6 (%) 8.4 (%) 4.2 (%)	Kumar et al. (2020) Ugare et al. (2014)
Vitamins	Niacin Riboflavin Thiamin	4.2 (mg/100 g) 0.10 (mg/100 g) 0.33(mg/100 g)	Kumari et al. (2021)
Essential amino acids	Cystine Isoleucine Phenylalanine Leucine Lysine Methionine Threonine Tryptophan Tyrosine Valine	175 (mg/g) 288 (mg/g) 362 (mg/g) 725 (mg/g) 78.33–122.33 (mg/g) 87.33–123 (mg/g) 231 (mg/g) 35.33–55.66 (mg/g) 150 (mg/g) 388 (mg/g)	Kumar et al. (2020) Kumar et al. (2020) Kumar et al. (2020)
Fatty acids	Linoleic Linolenic Oleic Palmitic Palmitoleic Stearic	46.4–48.1 (%) 1.5–1.7 (%) 27.6–28.2 (%) 17.4–19.0 (%) 0.4 (%) 4.3–4.5 (%)	Renganathan et al. (2020)
Lipids	Total phospholipids	8.0 (%) 5.5 (%)	Renganathan et al. (2020)
Carotenoids	Total carotenoids	36.7–50.8 (mg/100 g)	Renganathan et al. (2020)
Phenolic compounds	Total phenolic Total flavonoid Condensed tannin	45 ± 3.8 mg FAE/ g 8.7 ± 0.17 mg CE/g 7.1 ± 0.13 mg CE/g	Anis and Sreerama et al. (2020)
Bioactive compounds	GABA β-glucan	11.5–12.3% 5.0–6.0%	Kumari et al. (2021)
Anti-nutritional components	Phytic acid	3.30–3.70 (mg/100 g)	Panwar et al. (2016)
	Tannin	0.301(mg/100 g)	Gupta et al. (2013)
	Oxalate	0.02 (mg/100 g)
	Trypsin inhibitor	31.95 (mg/100 g)
Hydroxybenzoic acid	Gallic 3,4-dihydroxy benzoic Vanillic

Barnyard starch

Starch is the most fundamental component of the human diet, providing a range of nutritional properties (Lehmann and Robin 2007). Millets are among the principal sources of carbohydrates in India and Africa’s Sub-Saharan tropics and semi-arid tropics (Shivran 2016). Millets germplasms are categorized into two primary phenotypes depending on their amylose content: waxy and non-waxy (Vinoth and Ravindhran 2017). Barnyard millet has relatively low carbohydrate content than other major and minor millets, ranging between 51.5 and 62.0 g/100 g. (Saleh et al. 2013). The most abundant unsaturated fats in barnyard millet are linoleic acid and oleic acid. It demonstrates a significant amount of amylase retro-gradation, promoting the development of higher levels of resistant starch. It can be recommended for patients with cardiovascular type-2 diabetes (Rao et al. 2017).

The high carbohydrate to crude fiber ratio promotes a slower release of carbohydrates in the blood, improving blood sugar regulation. The resistant starch of barnyard millet has been found to significantly reduce blood serum, glucose, cholesterol and triglycerides (Renganathan et al. 2020). Barnyard millet is a gift from nature to humans since the millet provides low carbohydrates and digests slowly (Sharma et al. 2016).

Barnyard protein

Protein is the second most abundant macronutrient in millet grains after starch (Prasad et al. 2019). Barnyard millet has a protein concentration that is relatively higher than the protein content of other major cereals and comprises the crude protein content of 11.3–17.2% (Renganathan et al. 2020) and protein content of about 10.5% per 100gm (Ugare et al. 2014) that is easily digested (Kumar et al. 2020).

Shanmugapriya and Nazni (2020) found that the protein and carbohydrate content in 70 °C roasted barnyard millet flour was comparatively high. The influence of weather conditions, particularly temperature, is significant in affecting grain protein content (Prasad et al. 2019). The outer layers of barnyard millet are abundantly rich in proteins, antioxidants, omega-3 and omega-6 fatty acids (Sharma et al. 2016). Kumar et al (2020) evaluated the biochemical properties of different germplasms and observed that protein content ranged from 8.05 to 10.46%, with the highest and lowest protein content in the germplasm possibly owing to the genetic character of that germplasm. Non-essential amino acids, including proline, alanine, aspartic and glutamic acids, are prominent. The amino acid values of valine, leucine, isoleucine, phenylalanine and tryptophan vary from 31 to 102%, much above FAO scoring patterns. Cystine and methionine content account for 95% of the pattern levels, while lysine, with a score of just 39%, is limiting.

Barnyard dietary fibre

Dietary fibre is a plant-based material composed of various plant-based compounds that are not digestible in the human upper gastrointestinal system and can be found in the grain's cell wall (Rasane et al. 2015). According to Ugare et al. (2014), barnyard millet has richer crude fiber content than any other grain, ranging between 8.1 and 16.3%. Utilizing standard AOAC (1990) techniques, the total dietary fibre content of barnyard millet was found to be high (12.6%), including soluble dietary fibre (4.2%) and insoluble dietary fibre content (8.4%) (Ugare et al. 2014). Grain composition, particularly dietary fiber concentration, can be affected by contrasting environments (Miranda et al. 2013). The total dietary fibre content of barnyard millet seeds increases significantly during the germination bioprocess due to changes in the structure of the seed’s cell wall polysaccharides involving substantial cell wall biosynthesis, resulting in the formation of new dietary fiber (Sharma et al. 2016). Due to its significant antioxidant properties, whole-grain fiber protects against carcinoma such as breast cancer, while serotonin (monoamine neurotransmitter) relaxes the mood (Kumar et al. 2020).

Barnyard lipids

Oils and fats are crucial components of the human diet and the fat composition of millets ranges from 2 to 5% and barnyard millet has a fat concentration of 3.6 to 3.8% (Ugare et al. 2014). Barnyard millet's total lipids (free, bound and structural) are 8.0% (71.3, 21.2 and 7.5%) by dry weight. The significant classes and subclasses of barnyard millet lipids (in weight %) consist of neutral lipid (85.5%), glycolipids (9.0%) and phospholipids (5.5%). Barnyard millet contains a fair amount of Steryl Glycosides (SG) and Cerebrosides (CS) (Sridhar and Lakshminarayana 1992; Singh et al. 2022).

Most barnyard millet species have high fatty acid content (Kim et al. 2011). Barnyard millet provides a significant supply of unsaturated fats such as linoleic and oleic acids (Kaur and Sharma 2020). Linoleic and oleic acid are the most prominent unsaturated fats in the millet (Rao et al. 2017) at 46.4–48.1 and 27.6–28.2% respectively (Renganathan et al. 2020). In whole grains, palmitic acid varies from 17.4–19%, stearic acid from 4.3–4.5% and linolenic acid from 1.5–1.7% (Renganathan et al. 2020). Unsaturated fatty acids (oleic acid, linoleic acid and linolenic acid) make up about 85% of the total fatty acid composition. Compared to other crops such as rice, barley and wheat, barnyard millet varieties have very high linoleic acid contents (Kim et al. 2011). Other fatty acids in trace quantities include behenic acid, arachidic, and erucic acid. Millet oil has the potential to be an excellent source of tocopherols and linoleic acid (Sarita and Singh 2016).

Phytochemicals

Other than major minerals, barnyard millet comprises phytochemicals like phenolic acids, flavonoids and tannins, which act as natural antioxidants in the millet (Panwar et al. 2016). Barnyard millet is rich in bioactive compounds such as phenolics (free phenolic acid-protocatechuic acid, bound phenolic acid-ferulic acid), inulin, glucan, glucan, lignans, resistant starch, tocopherol, sterols, phytates and carotenoids (Sarita and Singh 2016) as well as some polyphenols including flavonoids, phenolic acids, tannins, coumarins and stilbenes (Gani et al. 2012). The principal polyphenols present are phenolic acids and tannins, with a trace amount of flavonoids; they serve as an antioxidant and play many roles in the immune system of the body (Chandrasekara and Shahidi 2010; Singh et al. 2022).

Total phenolic content in barnyard millet is found to be 45 ± 3.8 mg FAE/ g. Among the phenolic acids, p-coumaric, chlorogenic, caffeic and ferulic acids are the primary phenolic acids identified in barnyard millet (Anis and Sreerama, 2020). Flavonoids principally consist of flavonols, flavones, flavanones and anthocyanins. The flavonoid content in barnyard millet is 8.7 ± 0.17 mg CE/g (Anis and Sreerama 2020). Flavonoids are essential antioxidants that help reduce the risk of chronic diseases (Ofosu et al. 2020). Flavonoids provide numerous health advantages, including anti-cancer, anti-carcinogenic, anti-inflammatory, anti-allergic, antioxidant and gastro-protective characteristics. Condensed tannin contents in barnyard millet are 7.1 ± 0.13 mg CE/g (Anis and Sreerama 2020). Condensed tannins, which are composed of flavan-3-ol molecules, have antioxidant, anti-inflammatory, antiviral and antibacterial capabilities (Ofosu et al. 2020). Tannin level in processed barnyard millet flour is considerably lower than that of raw barnyard millet flour (Sarita and Singh 2016). Inositol hexaphosphate, often referred to as phytic acid is a bioactive molecule known to be a powerful antioxidant and is widely present in the bran portion of whole-grain cereals, namely the aleurone layer. (Lopez et al. 2002). In contrast to other cereals, barnyard millet has a reduced phytic acid concentration and trypsin inhibitory action. Barnyard millet inhibits a-galactosidase, a-amylase and acid phosphatase, more effectively and consists of about 3.30–3.70 mg phytic acid /100 gm (Panwar et al. 2016). Phytates protect against oxidative stress by chelating iron in Fenton's reaction, while certain phenolics and tannins function as antioxidants (Yabuno 2001).

Whole grain cereals provide more antioxidants than processed grains and phosphonic chemicals, phytic acid, carotenoids, lignans, tocols and alkyl resorcinols are among the antioxidants (Anis and Sreerama 2020). Several techniques for food processing, including heating, germination, hydrothermal treatment, fermentation and soaking, are found to significantly decrease or eliminate phytate content (Gupta et al. 2015a, b).

Micronutrients

Barnyard millet is a nutrient-rich, health-promoting grain abundant in vitamins and minerals, primarily vitamin B and magnesium which help reduce cholesterol while limiting bile acid release via insoluble fibre (Veena Bharati et al. 2005). It includes minerals such as manganese, iron, calcium, phosphorus and other nutritional minerals along with zinc, and magnesium (Renganathan et al. 2020). The total mineral content in barnyard millet is 2.7–4.2% (Shinde et al. 2021). It consists of minerals including calcium, copper, iron, magnesium, manganese, phosphorus, potassium, sodium and zinc in the amount of 17.1–32.7, 0.6, 15.6–18.6, 83, 0.7, 281, 298, 13–2 and 4.9 mg/100 g respectively (Table 1). It also includes vitamins B, riboflavin, folacin and thiamine, which are crucial in the body's energy synthesis (Sarita and Singh 2016). Some commonly found vitamins are niacin, riboflavin and thiamin in the amounts of 4.2, 0.10 and 0.33 mg/100 g respectively (Kumari et al. 2021).

Panwar et al. (2016) analyzed 5 different varieties of barnyard millet (PRJ1, VL21, VL29, VL172 and VL207) and observed that the calcium content in seeds of barnyard millet varieties ranged from 22.27 (VL29) to 27.10 (VL21) mg/100 g, iron content ranged from 19.27 (VL172) to 22.98 (VL29) mg/100 g, the zinc content from 4.21 (VL172) to 5.92 (VL207) mg/100 g, the copper content in seeds ranged from 0.013 (VL21). Mineral bioavailability is reduced by antinutrients such as phytates, polyphenols and tannins which chelate multivalent cations such as K⁺, Fe²⁺, Zn²⁺, Ca²⁺ and Mg²⁺ (Vinoth and Ravindhran 2017).

Processing of Barnyard Millet

The method used to turn grain into edible form and increase its quality is known as processing (Adebiyi et al. 2018). Minor millets can be used to make rice, flour, porridges, fermented products and ready-to-eat grains along with many other products following the processing techniques such as roasting, sprouting, popping and others (Jaybhaye et al. 2014). Various processing methods are adopted to increase barnyard millet grains or flour storage life as well as physicochemical availability of nutrients with decreased anti-nutrient content (Renganathan et al. 2020). Food processing methods are adopted to increase food components' digestibility, nutritional quality and bioavailability while reducing anti-nutrients (Sarita and Singh 2016). Some of the expected effects of processing on barnyard millet are mentioned in Table 2. Milling, decortications, boiling, soaking, fermentation, germination, malting, popping and other food processes are often used in the milling process (Sarita and Singh 2016). These processing methods are utilized to reduce anti-nutrients as well as to improve micronutrient's physiochemical accessibility and bioavailability Shanmugapriya and Nazni (2020) because millet grains have a hard seed coat and the husk (Fig. 1) can also be removed before they can be processed (Jaybhaye et al. 2014).

Table 2.

Effects of processing on Barnyard millet

Processing	Effects	References
Soaking	Reduces anti-nutritional compounds involving phytic acid and phytase activity and helps to improve the bioavailability of minerals	Sarita and Singh (2016)
Decortication or dehulling	Decreases polyphenolic pigments and phytate and phosphorus and improves the bioavailability of minerals	Panwar et al. (2016)
Germination	Decreases bulk density and porosity and make it less prone to auto-oxidation	Nazni and Shobana (2016)
Fermentation	Decreases anti-nutrient levels and improves the protein availability, digestibility leading to an appreciable change in the chemical composition of food material	Sarita and Singh (2016)
Milling & polishing	The degree of polishing, grain recovery increases at 14% moisture and the loss of protein, fat, ash and fiber decreases	Lohani et al. (2012)
Flaking	Reduces anti-nutrients such as phytates and tannins and improves the bio-availability of minerals, along with giving pleasing texture to the product and enhancing protein and carbohydrate digestibility	Mavila et al. (2000)
Puffing	Used for the preparation of snacks or breakfast cereals involving plain or with a few flavours/salt/sugars	Kaur and Sharma (2020)
Popping	Results in starch gelatinization that leads to endosperm bursting, which opens endosperm, giving a highly desirable flavor and aroma	Shobana et al. (2013)
Malting	Improves nutrient access and increases iron bio-accessibility by 300% and manganese bio-accessibility by 17%	Platel et al. (2010)

Fig. 1.

Flowchart for processing of barnyard millet

(Source Lohani et al. 2012; Gamel and Linssen 2008)

Soaking

Grain moisture is the most important criterion in barnyard millet as it influences storage properties (Renganathan et al. 2020). The moisture level of barnyard millet grain significantly influences its quality and the time required for milling and polishing (Renganathan et al. 2020). Grain with 8% moisture content is preferable for polishing than grain with 14% moisture content, but at 14% moisture, the extent of polishing enhances grain recovery and minimizes ash, protein, fat and fibre loss. The ideal moisture level for polishing is 10% (Lohani et al. 2012). Combining several processing methods like soaking, boiling and dehulling minimizes the number of antinutrients like phytate and polyphenols while improving protein digestibility in vitro and improving mineral bioavailability like iron and zinc (Pawar and Machewad 2006).

Germination

Germinated grains are widely consumed in the world, resulting in substantial changes in cereals' nutritional, biochemical and sensory properties due to the germination process (Sharma et al. 2016). Nazni and Shobana (2016) evaluated raw and germinated barnyard millet flour to develop different transportation and storage processing methods. It was observed that germinated flour had lower bulk density and porosity (air space) than raw barnyard millet flour. As a result of the decreased air space between the flour molecules, germinated flours are less susceptible to autoxidation than raw rice, which can help avoid flour spoiling, promote simple packaging and enables long-distance distribution (Renganathan et al. 2020).

Sharma (2016) observed that when un-germinated and germinated barnyard millet is compared, the free, bound and total phenolic content increases due to cell wall-degrading enzymes that become active during germination and change the grain's cell wall structure. Germination also enhances in vitro starch and protein digestibility of the millet (Shahidi and Chandrasekara 2013). Tannins also leach out of grains during the process of soaking and germination, which results in the decrease of tannins (Kumar et al. 2018). Sharma (2016) observed that during the germination bioprocess, tannin and phytate contents in seeds of barnyard millet decreased from 1.594–0.657 mg/100 g and 0.125–0.099 mol/kg respectively. Germination and probiotic fermentation substantially improve the protein, carbohydrates, soluble dietary fiber, total lysine, thiamine and niacin concentrations (Arora et al. 2011). Germinated seeds have more protein, fewer carbohydrates, unsaturated fatty acids and more vitamins and minerals. The mineral content of barnyard millet sprouts is higher in calcium, copper, zinc and phosphorus because of the phytic acid hydrolysis by the phytic enzyme activated during germination (Sharma et al. 2016; Chandraprabha and Sharon 2021).

Dehulling

The decortication procedure, also called dehulling, involves removing the bran (pericarp and germ) of millet grain to enhance quality characteristics such as grain color, palatability, fat content and phytic acid reduction (Siroha 2021). Dehulling is the primary unit process in converting millets into millet rice. Before the human consumption of barnyard millet, the grains must be adequately dehulled (Lohani et al. 2012). Gupta (2015a) observed the dehulling capacity of B29 and different barnyard millet varieties, including VL Madira 172 and PRJ1. He observed that after operating the thresher for 10 min, the dehulling efficiency of B29, VL Madira 172 and PRJ1 was 64, 45 and 26%, respectively and 70% of B29 grains were de-hulled, compared to 50% of VL Madira 172 and 29% of PRJ 1. Ugare et al. (2014) observed that the glycemic indices of dehulled and heat-treated grains are significantly lesser than glucose, this glycemic index reduction could be due to the formulation of resistant starch during heating and cooling cycles.

Fermentation

Fermentation is a metabolic process that uses microbes to transform complex material into a simpler form and is the most efficient and oldest technique of food processing and preservation (Siroha 2021). Srivastava et al (2021) performed fermentation of barnyard millet by Lactobacillus plantarum culture to enhance iron and folate content and observed that the tannin level in the raw samples is decreased by fermentation from 2.07 to 0.006 mg TAE/g. Tannin concentration reduction can be related to tannin binding with cotyledon endosperm due to its insolubility in the solvent or can also be due to bacterial phenoloxidase activity.

Fermentation of barnyard grains reduces anti-nutrient concentrations and increases protein availability and digestibility, leading to a significant change in the chemical composition of barnyard millet (Sarita and Singh 2016). Fermentation by L. plantarum culture significantly increases the 2, 2-Diphenyl-1-picrylhydrazyl; di(phenyl)-(2,4,6-trinitrophenyl) iminoazanium) (DPPH) radical-scavenging capacity from 25.4 to 35% in barnyard millet and employing LAB in fermentation processing improves the digestibility of protein and starch in grains (Srivastava et al. 2021). It is reported to improve the sensory qualities, palatability, nutrient composition and mineral availability (Siroha 2021).

Popping or puffing

Puffing grains is a traditional way of cooking grains to make snacks or breakfast cereals, either simple or adding additional flavors/salt/sugars (Kaur and Sharma, 2020). Popping is a processing method that employs sand as a heating medium in combination with the High-Temperature Short Time (HTST) method which results in starch gelatinization bursting of millets endosperm, which gives highly desired flavour and fragrance (Patel et al. 2013). During the popping process, the gelatinized starch component is released, resulting in an evident increase in seed size or volume (Gamel and Linssen 2008). Foxtail millet, finger millet, barnyard millet and proso millet can all be popped, proso millet has the highest popping yield of 92.77% and expansion volume of 6.51, followed by finger millet, foxtail millet and barnyard millet (Mishra et al. 2014). Several value-added products such as snacks, bakery items and breakfast cereals from popped or puffed barnyard millet grains can be formulated (Kaur and Sharma 2020). On a commercial basis, popping is being used to promote the consumption of barnyard millet grains as ready-to-eat meals (Saleh et al. 2013).

Milling

Milling is among the most conventional cereal processing procedures. Despite the growing popularity of whole millet grains, milling to produce flour is still the standard practice in cereal processing (Serna-Saldivar et al. 2016). There are two methods followed for barnyard millet milling: dry milling and wet milling. Dry milling produces flour, which is subsequently used to produce a range of millet goods such as bakery items, snacks, breakfast millets, brewing adjuncts, groats and leavened products such as cake, bread and fries (Ajibade et al. 2020). Removing starch and other modified components from cereals, such as germ, gluten meal and bran is known as wet milling (Serna-Saldivar et al. 2016).

The most common method for processing millets is milling to remove the outer bran (pericarp) of the grain, a procedure commonly found in rice that serves to lighten the color and contributes to the rapid cooking of products (Weber and Fuller 2008). A moisture level of 10% on a dry basis and a milling period of 3 min (Fig. 1) are best recommended for the optimum milling yield, polishing and broken in the barnyard millet (Lohani et al. 2012). Vijayakumar and Mohankumar (2009) observed that if pre-milling steps such as soaking and steaming are adopted before the barnyard millet's milling process, then pre-milling treatments significantly increase the water absorption capacity, grain hardness, swelling power, oil absorption capacity, protein content and dehulling yield. Protein, fat, ash and fibre content in barnyard millet decreases as moisture and milling time rise, primarily because of the removal of more bran (Lohani et al. 2012).

Thermal processing of barnyard

Thermal processing procedures include high-temperature pressure treatment, roasting, frying, microwave heating and extrusion (Kasote et al. 2021). Roasting is a rapid thermal processing method that implies dry-heat treatment for a short duration (Siroha 2021). Shanmugapriya and Nazni (2020) observed that when raw and processed barnyard millet were compared, the roasted barnyard millet flour protein, crude fat content and carbohydrate ranges were comparatively high at 70 °C playing an essential role in increasing the nutrients. Significant changes in phenolic values are observed due to the steaming of barnyard millet, and it is found that both steam and microwave treatments reduce the total phenolic content of barnyard millet (Pradeep and Sreerama 2015). Micronutrient denaturation, improved protein, antinutrient loss and starch bioavailability may occur as a result of the thermal processing of millet (Ajibade et al. 2020). Barnyard millet grains are also parboiled, dehulled and cooked similarly to rice (Surekha et al. 2013) and take about 12 min to cook using processing procedures, and the grain can be transformed into flour for the formulation of other food formulations (Renganathan et al. 2020).

Value-added products from Barnyard Millet

Consumers' demand for better, healthier, nutrient-dense foods has been rising recently (Kaur and Sharma 2020). The significance of diet in maintaining a healthy diet has substantially influenced cereal processing, resulting in the production of cereal-based products and industrial requirements to influence cereal processing (Nkhata et al. 2018). Millet grain production has a vital role in India's Food-grains economy as they account for almost one-sixth of total food grain production. Barnyard millet is a versatile crop that provides a significant supply of easily digestible protein as well as an excellent source of dietary fiber. It has lower carbohydrate content and is slowly digested, making it a suitable gift for people (Rao et al. 2017). Value-added products from barnyard millet can have an efficient industrial influence since customers consider that millets and millet-based foods improve their diet and health.

Barnyard millet for value-added foods

Barnyard millets can be a crucial food element in different regions. They can be used to make bread (fermented or unfermented), snacks, porridge and ready meals, baby foods, millet wine, millet nutrition powder and other conventional foods and beverages (Chandrasekara and Shahidi, 2012; Nisha and Saravanakumar 2019). Barnyard millets can be utilized in varying quantities ranging from 30 to 50% to develop standardized bread, cookies, cakes, soup sticks and Khari and traditional meals, such as millet-based value-added foods, can be standardized, such as breakfast recipes, sweet and snack recipes replacing rice and wheat. Idli, dosa, idiyappam, rotti, pittu, upma, vermicelli, adai, porridge, khakra and chappathi are some examples of breakfast foods Salunke et al. 2019).

One possible way to increase the utilization of barnyard millet is to blend it with wheat flour followed by appropriate processing (Singh et al. 2005). Many researchers have developed composite millet flours by partially substituting conventional cereal flours for preparing traditional meals and ready-to-use (RTE) food products (Jaybhyae et al. 2014). Surekha (2013) used a mixture of sago flour, pulse flour and vegetable flour to make barnyard millet cookies. Barnyard millet bran muffin and rusk were designed by Nazni and Karuna (2016) in which wheat flour was blended in varying amounts with barnyard millet bran making thin rectangular-shaped, steam-cooked cold extrudate trials and puffing them using the HTST puffing method to manufacture (RTE) barnyard millet (Echinochloa frumentacea)-based snacks.

Barnyard millet as a health food

Consumption of Barnyard millet is recommended for patients suffering from cardiovascular disease and diabetes. They are also the most effective at lowering blood glucose and lipid levels and are an excellent millet for celiac disease patients due to gluten intolerance (Kaur and Sharma 2020). Its flour is gluten-free and non-allergic, contributing to the prevention of gallstones and due to its high antioxidant activity, the whole grain fiber of the millet protects against carcinoma such as breast cancer, at the same time, serotonin (monoamine neurotransmitter) helps to calm the mood (Veena Bharati et al. 2005).

For celiac patients

Barnyard millet is gluten-free cereal, making it a suitable alternative to wheat and other popular cereal grains which contains gluten and are a concern for celiac patients or gluten-sensitive individuals (Saleh et al. 2013; Kaur and Sharma 2020). Thompson (2009) revealed that gluten-free grains such as sorghum, barnyard millet, kodo millet, tiny millet, corn, pearl millet, oats, quinoa and buckwheat have replaced items derived from wheat, rye and barley, which is beneficial to individuals maintaining a gluten-free diet. Therefore, barnyard millet is beneficial in lowering the consequences of celiac disease (Bunkar et al. 2021; Dey et al. 2022).

For diabetic patients

Barnyard millet has a high starch level but low sugar content, making it ideal for diabetic patients. In people with diabetes, the rising blood glucose can be reduced by substituting white rice with barnyard millet. Barnyard millet is recommended for people with cardiovascular disease and diabetes and is also ideal for reducing blood and cholesterol levels (Kaur and Sharma 2020). It helps general health by minimizing the risk of cardiovascular disease, constipation, type-2 diabetes and cancer. Barnyard millet is more effective at lowering blood glucose and cholesterol levels than other millets and rice.

The high dietary fibre content, low carbohydrate content (53–66%) and low digestibility can assist in the reduction of glucose levels (Veena Bharati et al. 2005). The beneficial impact of eating barnyard millet can be seen in higher High-Density Lipoprotein (HDL) levels and diabetic groups, and barnyard millet supplementation resulted in a moderate drop in triglycerides and an increase in HDL (Ugare et al. 2014).

Other uses of barnyard millet

Barnyard millet is one of the most-hardy millets, growing even under adverse agro-climatic conditions. It is a versatile grain in terms of nutrition since it contains a high concentration of macronutrients and dietary fibre (Ugare et al. 2014). With high grain characteristics and multiple levels of critical amino acids, minerals and vitamins, nutrient bioavailability can be enhanced further by lowering antinutrients (Vinoth and Ravindhran 2017). Some of the common food and industrial uses of barnyard millet are discussed in Table 3.

Table 3.

Utilization of Barnyard millet for food clinical and industrial purposes

Uses	Component of food	References
Flour	Used in the food preparations such as baby foods, snacks and dietary foods	Vijayakumar and Mohankumar (2009)
Composite flour	Convenience products such as extruded products including spaghetti, macaroni, vermicelli and noodles, pasta are made	Jaybhaye et al. (2014)
	Composite flour plays a vital role in increasing the concentration of protein, fat and ash	Singh et al. (2005)
Packaging material	Rich in amylose and is used in biodegradable film-making industries as an antioxidant packaging material	Cao et al. (2017)
E. esculenta extract	It has high anti-mutagenicity against 3-(5- nitro-2-furyl) acrylic acid in strains of Salmonella typhimurium due to higher polyphenolic content and also acts as an antioxidant by scavenging H2O2 radicals	Brindzova et al. (2009)
Value-added products	For the preparation of products like biscuits, sweets, vermicelli, ready mixes, multi-grain atta (flour)	Sood et al. (2015)
Health food	Recommended to infants, pregnant women, diabetic-celiac patients and patients intolerant to gluten and allergic to wheat-based products	Patil et al. (2017)
Probiotic and prebiotic	Fermented millet products protect against diarrhea in young children and promote digestion and act as natural probiotic	Sarita and Singh (2016)
Future crop	Tolerant to drought and flooding conditions and has higher efficiency of using nitrogen over cereal crops	Goron and Raizada (2015)

As antioxidant

Polyphenols are the major antioxidants that significantly contribute to the antioxidant activity of cereals and flavonoids are effective antioxidants that prevent the development of chronic diseases. Barnyard millet has a Total Phenolic Content (TPC) of approximately 129.5 ± 4.95, a Total Flavonoid Content (TFC) of approximately 101.3 ± 10.4 and a total condensed tannins content (CTC) of around 59.54 ± 4.63 (Ofosu et al. 2020). Condensed tannins, which are made up of flavan-3-ol units, have antioxidant, anti-inflammatory, antiviral and antibacterial effects. The principal polyphenols present are phenolic acids and tannins, with a trace amount of flavonoids; they serve as an antioxidant and play many roles in the immune system of the body (Chandrasekara and Shahidi 2010).

Medicinal uses

Barnyard millet is a unique food that has the potential to become a decent substitute for increasing diabetes mellitus (Ugare et al. 2014). It also has a high concentration of polyphenols and phytochemicals, which are antifungal and antibacterial. Dietary fiber aids in the prevention of hyperglycemia, and phytates help prevent oxidative stress and certain phenolics and tannins function as antioxidants. Processed barnyard millet flour is an excellent ingredient for infant food and beverages (Anbalagan and Nazni 2020). According to Shanmugapriya and Nazni (2020) processed barnyard millet can be recommended as an alternative to WHO-ORS for diarrheal replacement fluids.

As future crop

Barnyard millet (Echinochloa species) has emerged as one of Asia's most important minor millet crops with a raised worldwide production (Renganathan et al. 2020). Barnyard millet is a short-season crop that can thrive in challenging climates with little input and tolerate various biotic and abiotic conditions, thus referred as ‘a resilient multipurpose crop’ (Saleh et al. 2013; Maithani et al. 2022; Padmaja et al. 2022). It is cultivated mainly for human consumption and livestock feed (Renganathan et al. 2020). Regarding protein and calcium content, barnyard millet crop straw is considered a superior feed to rice, oat, or wheat straw (Yabuno et al. 1987). It is an excellent supplementary crop for farmers and an alternate crop in rice or major crop farming regions after rainfall failure (Gupta et al. 2009).

Industrial applications

Barnyard millet starch, rich in amylose, is gaining popularity as an antioxidant packaging material in the biodegradable packaging sector (Renganathan et al. 2020). Employing aqueous extract obtained from aerial sections of the E. colona plant and further used to produce Silver Nanoparticles (AgNPs) for the formulation of a unique eco-friendly alternative to bio-synthesizing nanoparticles in plants. Such AgNP synthesis from plant extracts can be a safe and ecologically friendly approach for large-scale applications, including medicine, engineering and agriculture (Kumar et al. 2016). When borage seed oil is added to barnyard millet starch, it enhances its elongation range while decreasing its tensile strength, water permeability and moisture content, making it appropriate for biofilm development (Renganathan et al. 2020). Due to its greater feed quality, higher digestibility and nitrogen concentrations, barnyard millet is employed as a possible animal feed crop from the dry regions of the Deccan plateau to the extreme hills of the temperate sub-Himalayan region (Renganathan et al. 2020).

Conclusion

Nutritional security depends on the population's diet to maintain the global population's health status. Barnyard millet is a great staple food source that provides all of the nutrients in the diet and some health benefits. It can help with specific health and diet problems such as malnourishment, diabetes, cardiovascular disease, obesity, skin problems, cancer, celiac disease, and other diseases. Barnyard millet's nutrient content opens up new possibilities for incorporating it into functional food products. This crop can thrive in adverse agro-climatic conditions, and grains have benefits as a draught-resistant crop that is less susceptible to biotic and abiotic stresses, provides high yield productivity due to multiple harvests per year and can easily survive in water-stressed areas. Significant efforts are required to develop varieties or hybrids with farmers/consumers of desired traits. Barnyard millet has the potential to be a crop for micronutrient bio-fortification. A shift in consumer preference toward minor millets, combined with the development of suitable food products and an increase in market price, would result in higher returns for farmers and healthier options for consumers. Further research and development are required to produce functional foods by incorporating previously unknown aspects of millet to make it a promising crop for long-term food and nutritional security in future climate scenarios.

Abbreviations

FAO

Food and Agriculture Organization

SDG

Sustainable Development Goal

ICRISAT

International Crop Research Institute for the Semi-Arid Tropics

MT

Metric ton

SG

Steryl Glycosides

CS

Cerebrosides

DPPH

2, 2-Diphenyl-1-picrylhydrazyl; di(phenyl)-(2,4,6-trinitrophenyl) iminoazanium)

HTST

High-Temperature Short Time

HDL

High-Density Lipoprotein

TPC

Total Phenolic Content

TFC

Total Flavonoid Content

FAE

Ferulic acid equivalent

AgNPs

Silver Nanoparticles

Author's contribution

DB, PR and JS planned, conceptualized and developed the manuscript, SK and PR supervised and reviewed. MF, JK and MG analyzed and interpreted the data. DKM and CMM provided necessary technical inputs and proof read the manuscript to present it in its current form. HA and NS formulated the illustrations and integrated them with the manuscript.

Funding

The authors declare no funding supports was acquired from any source for this work.

Data availability

Data sharing not applicable to this article as no datasets were generated or analysed during the current study.

Declarations

Conflict of interest

The authors declare that there are no conflicts of interest.