Millets are annual small-seeded cereal crops grown all over the world for food, feed, forage and fuel. There are about 20 different species of millets. Commonly cultivated species include proso millet (Panicum miliaceum
L.), pearl millet (Pennisetum glaucum
(L.)R.Br.), finger millet (Eleusine coracana
Gaertn.), kodo millet (Paspalum scrobiculatum
L.), foxtail millet (Setaria italic
(L.) P. Beauvois), little millet (Panicum sumatrense
Roth ex Roem. & Schult.) and barnyard millet (Echinochloa esculenta
(A.Braun) H.Scholz) [1
]. Though they belong to the Poaceae
family, a significant morphogenetic diversity exists at species, genus and subfamily levels. They differ at their genome size, ploidy levels and breeding systems [2
]. Millet is the world’s sixth most important cereal grain supporting as a major source of energy and protein for millions of people in India, Africa, and China, and especially for the people living in arid and semiarid regions [3
]. Millets are cultivated globally with major contributions from India, Nigeria, Niger, China, Mali and Burkina Faso [4
]. Asia (48%) and Africa (48%) dominate the production of millet compared to Europe (3%) and America (1%) (Figure 1
]. Short duration and wide adaptability under different environmental conditions make millet one of the most suitable crop for sustainable agriculture and future food security [1
]. Millets can give significantly higher yields on marginal lands with low fertility and low input agricultural systems compared to many other crops. Millet can serve as a savior for the world’s rapidly increasing population with the potential to avert food shortage and famine.
Proso millet (PM) is popularly known as Broomcorn millet (China), Common millet (USA), Barri (India), Broomtail millet, Kashfi Millet, Red Millet, and White Millet, Brown Millet, Chinese Millet, Kibi, Mijo (Spain), Panic Millet (France), Gijang (Korea) (Figure 2
]. PM was domesticated in 8000–10,000 BP in northern China. PM is distributed around the world for its wide adaptability in different climatic zones [1
]. It is widely cultivated in India, China, Nepal, Africa, Russia, Ukraine, Belarus, Middle East, Turkey and Romania. It was introduced in North America in 1875 by the German-Russian immigrants, who planted along the eastern Atlantic coast [1
]. It is one of the best-suited crops for the rainfed agricultural system where annual rainfall is ≤100 mm [8
]. The shallow root system (90–120 cm) and short growing season crop (60–90 days) make it an ideal dryland crop [10
]. In the USA, it is grown as a dryland crop on an average of 204,366 ha land [12
]. Its production in the Central Great Plains (CGP) is mainly concentrated in the states of Nebraska, Colorado and South Dakota [8
]. Proso millet is an important rotational crop used in CGP following sunflower (Helianthus annuus
L.) and corn (Zea mays
L.) because of the short growing season and high-water use efficiency [9
]. The short growing season allows farmers to harvest the millet prior to sowing the winter crops. This is an important feature as winter wheat serves as the base crop for most of the dryland cropping system.
PM is an under-utilized crop although one-third of protein and energy in developing countries are derived from it. The major market share for PM is contributed by birdseed industries. Irrespective of several health benefits, including gluten-free, low glycemic index, high protein, and fibers, PM is still struggling to enter human food markets. Recent increases in gluten-free trends and escalation in health consciousness among people have created renewed interests in ancient grains. The human food market for PM has found its way to different breakfast cereals, bakery products, fermented products and brewing. Promotional marketing, research for the development of new varieties, and awareness among farmers and consumers are necessary to revive the lost ancient trend where PM was common in cuisines of different communities.
There are few review papers on millets for human health and environmental sustainability. However, there is no such review article specifically on PM. Therefore, the purpose of this paper was to provide comprehensive information on PM for environmental benefits and human health, its socioeconomic importance, and PM-based food around the world.
The following methods were used to for this paper. We undertook a literature search for relevant studies (peer-reviewed journals, and news articles) especially addressing the purpose mentioned above. Primary keywords used in search were proso millet, drought, climate, health benefits, ancient grain and water use efficiency. As an inclusion criterion, we tried to incorporate the most recent studies and a few old relevant reports for which no recent reports were available.
Due to a lack of published information on PM-based food around the world, we thought that the best way to gather information is through personal communication with PM scientists in countries growing millets from ancient times. We hypothesized that the countries growing millets for this long should have this cereal as an important ingredient of their food culture. Thereafter, we identified proso millet research groups working on health benefit aspects and developing different food recipes. Then, based on our past attendance of the International Broomcorn Millet Symposium (1st in 2012: China; 2nd in 2015: Korea, 3rd in 2018: USA), we communicated (via emails) with the scientists in USSR, Japan, Korea, and Europe (Germany, Switzerland, Italy) and India.
4. Proso Millet as Human Food and Health Benefits
Nutritional quality is the key element that determines the dietary importance of a grain and its importance towards human health. PM is known for several health benefits. It has high nutritive value and is comparable to major cereal grains (Table 2
). PM is a good source of minerals like calcium, phosphorus, potassium, sodium, magnesium, manganese, iron, magnesium and zinc (Table 3
). PM has all the essential amino acids viz. methionine, phenylalanine, tryptophan, valine etc. [43
] (Table 4
). The limiting amino acid in PM is lysine, which is only 189 mg/g (Table 4
). The essential amino acid index was found to be higher (51%) in PM compared to wheat [44
]. Major nutritional component protein, carbohydrate, and energy values are comparable to popular cereals like rice, wheat and barley (Table 2
). PM has 11% (which may range from 11.0% to 14.0%) of protein per 100 g of grains, compared to that of wheat (14.4%) and rice (7.5%) (Table 2
]. Moreover, PM has a low glycemic index (GI) compared to rice, wheat, and barley, which makes it an ideal food for people with type-2-diabetes mellitus and cardiovascular disease (CVD). Products prepared with 100% PM showed GI (%/g) of 50–65 compared to 70–80 of refined corn and wheat-based products [46
Sedentary lifestyle and food habits are the primary cause of diabetes, obesity and cardiovascular diseases. Therefore, dietary modification is an important preventive and protective measure against all metabolic disorders. PM protein (PMP) has an important role in cholesterol metabolism as they can increase concentration of the high-density lipoprotein (HDL) cholesterol level, especially the isomer HDL2, and adiponectin without affecting the concentration of low-density lipoprotein (LDL) cholesterol. Adiponectin is important in accelerating insulin sensitivity and promotes lipid metabolism [47
]. Clinical studies showed that lean people have more adiponectin compared to obese people [48
]. Research by Park et al. (2008) clearly indicates upregulation in the expression of adiponectin in PMP diet modules [49
]. Elevated levels of HDL in bloodstream also can help in maintaining blood LDL level and can protect endothelium or inner walls of blood vessels from any damage. Damage to inner walls of blood vessels is considered as the first step in the process of atherosclerosis, which is the reason for heart attack or stroke [50
]. Thus, feeding of PMP can actively reduce blood glucose and insulin levels under high-fat diet conditions by elevating levels of HDL and adiponectin. PMP also downregulate tumor necrosis factor alpha (TNFα) and increase insulin sensitivity as both are negatively correlated [49
]. Dietary improvement and avoidance of gluten is the only nutritional therapy available for a person suffering from celiac disease. As in this disease, people are allergic to gluten (a protein found in the wheat, rye, barley, oats etc.). On average 1% of the European and US population is suffering from celiac disease [51
Nutrient composition of PM has been evaluated by many authors, [43
]. PM has high mineral content that includes calcium, iron, potassium, magnesium, phosphorous, zinc, dietary fiber, polyphenols and protein (Table 3
). PM contains a high amount of lecithin which plays an important role in the neural health system by repairing and regenerating myelin fiber and intensifying brain cell metabolism. PM also contains a significantly high amount of vitamin B-complex, folic acid and niacin [52
]. The mineral content of PM is much higher in comparison to major cereal grains. High content of fiber, and antioxidants in PM is also valuable in prevention of CVD and cancer. A study by Zhang et al. (2014) showed antiproliferative properties of PM against MDA (originally isolated as part of the MD Anderson series of breast cancer cells; hence MDA) human breast cancer and HepG2 human liver cancer cells [54
]. PM in regular diets can lower cholesterol, TNFα, phytate, and increase HDL and adiponectin. An increase in HDL and adiponectin can reduce the risks of many hormone-dependent cancers, CVD and breast cancer [1
]. PM can be used as a prebiotic. Non-digestible carbohydrates in PM helps in the growth of desirable microflora in the intestine. It can prevent constipation and is, therefore, quite effective as preventive food against colon cancer [56
5. Proso Millet vs. Quinoa
In the last few years, the market share of ancient grains has increased rapidly. Nutritional benefits of ancient grains have created a rapid hype in the health food market [58
]. PM and quinoa are two popular grains which resemble each other in many characteristics including seed shape, color and nutritional profile. Though their similarities, PM, which is long known for the health benefits, could not generate much hype in consumers despite being lower priced (US $
4.4/kg) compared to quinoa (US $
15.4/kg). In the last decade, the export of quinoa has exponentially increased in developed countries including the USA and UK. The exponential increase has also created distressing ecosystem and imbalance in regional markets. It indicates a big gap between the available information on nutritional profile of PM to consumers and stakeholders. The lesser known and underutilized PM have similar nutritional qualities to substitute quinoa in a more sustainable way. We tried to provide a comparative study between PM and quinoa to provide a better understanding of the differences.
Quinoa and PM are gluten-free with a low glycemic index, rich in protein, vitamins and minerals (Table 5
). Protein content is higher in quinoa than in PM. While both quinoa and PM are rich in all the essential amino acids, lysine is low in PM. Both quinoa and PM are rich also in dietary fiber and antioxidants. Therefore, the nutritional composition of quinoa and PM is essentially similar except for protein content.
Quinoa seed can be white, red, black and purple, while PM seeds can be white, red, yellow, or black. Quinoa seeds are oval or disk-shaped while PM seeds are mostly circular. Both PM and quinoa seeds have mild flavors.
Price Hike and Ecosystem
A wave of superfoods in developed countries like the US and UK has led to the relatively unknown commodity quinoa to become an upper-class staple in the last decade. Import of quinoa to the US has witnessed a tenfold increase from 0.24 million kg per year in 2004 to 3.37 million kg in 2017. Price has also quadrupled in these years [59
]. Rise in price has raised several questions and concerns regarding welfare of individual and households where quinoa is traditionally produced and consumed (Peru, Bolivia, Colombia, and Ecuador). One study by Blythman (2013), which was published in the Guardian claimed the following: “There is an unpalatable truth to face for those of us with a bag of quinoa in the larder. The appetite of countries such as ours for this grain has pushed up prices to such an extent that poorer people in Peru and Bolivia, for whom it was once a nourishing staple food, can no longer afford to eat it. Imported junk food is cheaper. In Lima, quinoa now costs more than chicken. Outside the cities, and fueled by overseas demand, the pressure is on to turn land that once produced a portfolio of diverse crops into quinoa monoculture
]. In terms of ecological consequence, the growth in the consumption of quinoa in non-indigenous regions has led to intensive farming of the crop, which expanded quinoa farming into ecologically brittle ecosystems [61
In comparison, locally grown PM in the High Plains of the USA can potentially substitute quinoa in a more beneficial way. Increase in consumption of PM can improve economy of farmers in the High Plains and producers and can compensate economic loss of importation. The cost of PM (US $4.4/kg) is also several folds lower than that of quinoa (US $15.4/kg), which makes PM a common man’s food rather affluent people. A balance between regional food and imported food will be beneficial for maintaining a sustainable ecosystem both in exporting and importing countries. Equilibrium in demand and export/import ratio will also reduce price spikes which has quadrupled in last few years.
6. Proso Millet Based Foods and Beverages across the World
Traditional use of PMs in cuisines of Russia, Germany and China dates back to 8000–10,000 BP. Russians used it in preparation of a sweet dish by mixing with milk and sugar, or sometimes consumed as savory mixed with meat and vegetables. Chinese people used to consume it without milk and sugar, frequently mixed with different vegetables like beans, potato or squash. In Germany, people also used to take it as a sweet dish added with apples and honey [64
Potential health benefits of PM grain have attracted several food industries in Europe and North America. Mild flavor with light color and gluten-free properties is ideal for making bread for people suffering from celiac disease [1
]. Many industries produce bread, pasta, flour and couscous-like products with PM alone or in combination with other grains. The gluten-free food market in the US is growing, which is evident from the increase of the 0.9 billion dollars market in 2006 to 10.5 billion dollars in 2015 and is expected to be 23.9 billion dollars by 2020 (Figure 3
]. Research on product quality and nutritional value of the food produced from PM and comparison with popular grains showed positive results [15
]. A recent study by McSweeney (2017) compared four different food products, viz. muffin, couscous, extruded snacks and porridge, made from refined PM and refined corn for their in vitro starch digestibility, nutritional composition and expected glycemic index (eGI). Interestingly, they found that the products made from refined PM with the maximum concentration had significantly (p
< 0.05) less eGI compared to corn and corn proso mixed products and were gluten-free [46
]. However, the absence of gluten often makes it hard for the bread industry to make a proper dough. However, this can be addressed by the addition of hydrocolloids like xanthum gum, guar gum [67
PM-based food products can be categorized into porridges, steamed cooked products, bakery products, beverages (PM Tea) and fermented products.
6.1. Porridge and Steamed Food
Porridge is one of the most popular dishes made from PM. Though porridge recipes across different countries and communities is similar, lack of proper documentation is still a major hindrance in popularization. For information on porridge across the world, we had personal communications via e-mails with appropriate scientists in a few important countries where PM is common. According to Dr. Galina Suvorova, head of the department of genetics and biotechnology from the All-Russia Research Institute of Legumes and Groat Crops, PM is one of the popular foods in her country, which is sold as groats (dehulled seed) (Russian name of millet groat is “psheno” (пшeh
o)) (Figure 4
a). Groats are usually boiled with water or milk to prepare the porridge. In Russia, the preparation is known as “Kasha” (Figure 4
b,c). In Korea, the porridges are prepared by boiling millet in water and adding honey and eggs (Information from Dr. Hijin Kim and Cheol Ho Park, Kangwon National University, Korea) (Figure 4
d). Rice-based meals and noodles are major steamed foods used in Japan and Korea. Steamed noodles (Jinju noodles), and rice meal (Ogokbap, Gohan) are famous in Japan and Korea (Figure 5
a,b). Migliaccio, another regional dish from Italy, is prepared in the winter months with hog blood, millet flour, chocolate and milk. Polenta, a historic dish of Italy which is now prepared with corn flour, was prepared with millet in the 16th century. Panissa (the term originating from Panicum), a risotto-like dish, was originally made with millet and was popular in the Piedmont area of Italy (Information from Dr. Silvano Ciani, Lead Corporate Research & Innovation—Basic Research, Trieste, Italy).
6.2. Bakery Products
Bakery products hold the maximum uses of millet among all these categories. Shadang and Jagnathan (2014) used different proportions of PM, finger millet, foxtail millet, pearl millet with added wheat flour to prepare cookies, cakes and biscuits. Sensory evaluation suggested acceptable taste and flavor among products [68
]. Several food technologists tried different combinations of millets including proso, pearl, barnyard, foxtail and sorghum to find out an acceptable ratio of mixing, followed by their nutritive evaluation [69
]. Multigrain bread is the most popular among the bakery products. A study by Kamaraddi and Shanthakumar (2003) tried different concentrations of millet mixture to test dough characteristics. They concluded that wheat flour can be substituted to 10%–20% with millet flour for dough preparation. PM can be used to substitute 15% wheat flour used for bread making in comparison to the 10% substitution index of finger, foxtail and little millet [71
]. Balloi et al. (2014), found out that 50% flour composition can be replaced with the millet composition [72
]. Bakery products produced with combination of PM flour showed lower glycemic index compared to refined flour (Table 6
). Anju and Sarita (2010) tried preparation of biscuits out of foxtail millet, barnyard millet and refined wheat flour in combination with hydrogenated fat, eggs, curd and baking powder. Sensory evaluation of the product also revealed overall acceptability and a low glycemic index compared to wheat flour biscuits [73
6.3. Fermented Products and Beverages
Two common fermented products are dosa (Figure 5
c) and noti (Figure 5
d). Dosa is an Indian pancake and is made from fermented batter using 2:1 millet and black grams. Noti is a Korean pancake and is prepared with broomcorn millet in many regions (personal communication with Dr. Hijin Kim and Dr. Cheol Ho Park).
Different countries have their own traditional millet-based fermented alcoholic drinks. Gluten-free beverages are growing fast in European and American beverage production industries. In the US, especially brewing companies from the Great Plains, have started producing beers using PM as a base ingredient. Companies like Colorado Malting Co. (Alamos, CO), New Planet Beer, Eddyline Restaurant and Brewing Co., and Pagosa Brewing have already started preparing malts and beer from PM (personal communication with the breweries). In the state of Nebraska, Modern Monks Brewery in Lincoln has brewed beer using PM [64
]. PM is an important malting material for its high amylase activity. Malt from PM was used in substitution of barley in the European countries during World War II [74
]. Traditional brewing of beer from millet has been descending in many tribes for ages. The people of Nepal or eastern Himalayan parts of India (Darjeeling and Sikkim) use millet as a base ingredient for fermented alcoholic beverages like Tongba (Figure 6
a,b) Rakshi and Marcha [64
]. Romanian and Bulgarians used to make fermented drink Boza out of millet. Likewise, people of the Orchid Island in Taiwan produce traditional fermented beer from millets [64
]. Fermented millet beverage Jiu was mentioned in ancient Chinese text (1200–1000 BC) [74
]. Sur is another millet-based fermented drink of Himachal Pradesh, India. It is mainly prepared with a mixture of roasted barley, local herbs (“Dhaeli”), and millets. Alcohol content of the drink may vary from 5% to 10% [76
]. Madua is one of the most popular millet-based drinks of Arunachal Pradesh, India. Millets are roasted and softened by boiling, mixed with starter culture and left for 4–7 days for fermentation. Other millet-based drinks of the state are Themsing, Rakshi, Mingri, and Lohpani [77
]. Oshikundu is a traditional fermented beverage of Namibia which is sour-sweet in taste. Koozh, a fermented beverage from Tamil Nadu, India, is generally made with millet flour and rice [15
]. Suutei Tsai (Figure 6
c,d) is a famous Mongolian tea prepared with milk, salt, green tea and millet [78
8. Socio-Economic Aspect of Millet
PM is one of the ancient millets in many countries in the world mainly in semiarid and drought-prone areas. PM is mainly consumed as food in those cultures from ancient times and it had a pivotal role in the early development of multi-crop agricultural systems and settling of the farming societies [80
]. PM and other millets were replaced by higher yielding crops like wheat, corn, soybean in agricultural system of those countries during 20th century. As a result, the significance of PM and other millets in rural socio-economy was greatly reduced in the last century agrarian system. However, PM, like many other millets, are getting renewed attention in millennial agriculture owing to the awareness of millets as climate smart crops and their human health benefits.
Professor Martin Jones, a renowned archaeobotanist and archaeogeneticist at the University of Cambridge, has conducted extensive research on ancient farming practices in Europe and China [81
]. He identified foxtail and PM as two key Asian millet species in the prehistoric crop records in Europe, suggesting their widespread presence in ancient farming systems. Professor Jones also reported that an ancient multi-crop farming system, which included millets, is still practiced in Aohan and Mongolia. The Aohan Dryland Farming System has been recognized as a ‘Globally Important Heritage Systems’ site by FAO. The millet from Aohan has witnessed a recent surge in sales as a high-quality product in the local Chinese market [81
]. Similarly, PM is getting significant attention in several European countries like Poland, Slovenia, Switzerland and Germany [82
]. Significant research is being conducted in the areas of use of PM in specialized organic breakfast cereals, organic poultry feed and gluten-free food. Thus, PM will be playing important role in the rural socio-economy of those countries.
PM is also getting similar renewed attention in the USA. On March 11, 2017, a millet commission named “High Plains Millet Association (HPMA)” was formed in the High Plains of the USA. The mission of the HPMA is to “provide sustainability to the millet industry through research, production, and marketing” [84
]. The comparable nutritional profile with wheat along with gluten-free characteristics can itself give millet an expanded market in the gluten-free food sector. Only a small fraction of the PM grown in the USA goes to the domestic food market, while the majority goes into the birdseed market. HPMA has encouraged farmers to opt for other market aspects of PM including a gluten-free human food market, and livestock food markets like dog, hamsters, swine, sheep and cattle. An expanded PM market will only be able to generate more revenues for research and development. The current funding prospects in PM are less, which is another limiting factor in PM research and development. Recent proposals from HPMA also suggested that the Agricultural Marketing Act should be amended to include PM as an agricultural commodity so that the PM producers and handlers can vote for the referendum to approve different marketing orders and assess the funding for education, research and promotional programs [84
In India, the notion of the importance of millets started changing with the realization of the immense agronomic, environmental and nutritional benefits these crops offer [88
]. The National Food Security Act of 2013 has particularly given the highest priority to millets among coarse grains. The M.S Swaminathan Foundation has requested an amended policy to investigate small millets and their potential role for climate-smart agriculture [88
]. The report by Padulosi et al. (2015) also showed the importance of minor millets including PM in economic and nutritional sustainability of rural India. The majority of the Indian population is economically unable to afford an expensive balanced diet [89
]. Thus, promoting use of underutilized millet is a powerful way contributing nutritional security along with economic growth of rural Indian populations. In southern India, the government of Tamil Nadu has started including millet in school meals with different recipes along with rice and wheat to boost its wide acceptance and cultivation. Scientists in International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) had also started working on HarvestPlus programs to improve the nutritional content of millet to support daily intake of iron and zinc, which are vital for the mental and physical developments of children [90
9. Future Prospect and Perspectives
PM is one of the miracle grains with several environmental and health benefits. They can be used to control annual grass weed, insect pressure, and disease incidence in wheat [9
]. They are economically important rotational crops for the semiarid regions. They conserve the soil water level and can produce significant yield at marginal lands. PM can play an important role in global food security under changing climate [1
]. Water shortage is a major threat for agriculture in future and urges a shift in farming practices. Inclusion of PM in cropping systems could play an important role in water shortage mitigation [38
]. Activities associated with an ever-increasing population has also degraded the inherent soil quality. Almost 66% of the topsoil has been lost in the last decade and every year 0.001 t/ha of flat land with grass or forest cover, 1–5 t/ha of mountain regions with vegetation are eroded [25
]. PM also could play an important role in addressing this issue.
Adoption of a PM-based diet can potentially prevent deterioration of human health resulting from a sedentary lifestyle. PM can lower the risk of cardiovascular disease, and type 2 diabetes and can help in maintaining obesity levels [49
]. Although a number of research articles emphasizing potential health benefits have been published, industrial application of PM is still facing major competition. There is still a broad gap in studies delineating the nutritional composition of different millets, their agroecosystem, health benefits and applications in food industry. Studies defining different processing methods and different food applications are necessary to promote its wide applications in different market sectors. Production and market gaps will only be overcome by educating people about prospects of millets including both nutritional and environmental values. Additional market research and promotion of this alternative crop for a healthy diet and lifestyle is necessary for wide acceptance and consumption.