Millets are a group of cereal grains that belong to the Poaceae family, commonly known as the grass family. They constitute an important source of food and fodder for millions and play a vital role in the ecological and economic security of India. These millets are also referred to as ‘coarse cereals’, ‘nutricereals’, ‘cereals of the poor’, etc. Millets are highly adaptive to a wide range of environmental conditions such as floods, drought, etc. They have minimum requirements for water, fertilizers and pesticides. They are rich in proteins, vitamins and minerals. They have a low glycemic index, making them ideal for people with diabetes. Millets are a good source of iron, zinc and calcium.
Millets are usually rich in proteins, with some millets being highly rich in sulphur-containing amino acids like methionine and cysteine. The functional properties of millet proteins influence cooking and other secondary processes. The properties of these proteins are affected by multiple factors such as pH change, drying, freezing, heating, ionic strength, storage conditions and physical, chemical and enzymatic modifications, (Amadou et al., 2013). Due to the high nutrient contents of millet, they have undergone a few modifications throughout generations and are still in progress to become an alternate source of energy-giving diet in place of rice, wheat and other carbohydrate-rich cereals. (Chemistry, 2015)
Sorghum is the fifth most-produced cereal crop in the world. It is low in fat, but is rich in protein, B vitamins, fibre and micronutrients, all of which contribute to good health. This grain is a good source of plant-based protein. The major portion of sorghum protein is prolamin which has the unique feature of lowering digestibility upon cooking and is significantly less digestible than other cereal proteins. Sorghum is gluten-free and hence it is a great food for diabetic patients. It promotes the health of bones. They are also rich in antioxidants.
Prolamins and glutelins are the major sorghum protein fractions, where prolamins namely kafirin is predominant, (Pontieri & Del Giudice, 2015). Lysine is the most limiting amino acid in diets containing sorghum. The protein content of 44 genetic varieties of grain sorghum shows that the lowest value is 8.61% and the highest is 18.21%. The principal proteins of sorghum endosperm are prolamins and glutelin. Albumin and globulin together account for less than 12% of the total endosperm protein. This distribution of various protein fractions in sorghum endosperm is similar to that of corn endosperm proteins.
The increased protein content in sorghum varieties may be attributed mainly to an increase in the prolamins fraction of the grain. The basic amino acids such as lysine, histidine and the sulphur containing amino acids are deficient in sorghum varieties. Whereas glutamic acid, proline, alanine and leucine are present in higher concentrations. Concentrations of lysine, arginine, glycine, cysteine and methionine in the globulin fraction are nearly twice that of the endosperm meal and several times higher than those present in the prolamins fraction. On the other hand, the levels of glutamic acid, proline, alanine and leucine in the globulin fraction are about half that of the concentrations of these amino acids in endosperm meal and the prolamins fractions. The amount of tyrosine, histidine, arginine, glycine and cystine present in the glutelin fraction is several times higher than that of levels of these amino acids in the prolamins fraction.
Concentrations of glutamic acid, valine, leucine and phenylalanine present in the endosperm meal are higher than those in the individual protein fractions. This may be due to some residual protein fraction, which cannot be extracted from endosperm meal that has higher levels of these amino acids.
Environmental factors influencing protein and amino acids in sorghum are location, chemical fertilizers, plant population, herbicides, amino acid availability and digestibility. Any attempt to enhance the protein content of grain results in decreasing the nutritional quality. Application of herbicides at sub-herbicidal concentrations is known to increase the protein content of several crops. Certain phenolic compounds are called tannins, which decrease the digestibility of sorghum protein. (HARDEN et al., 1976)
Pearl Millet (Bajra)
Pearl millet is also known as bajra and is grown in semi-arid regions, primarily in Africa and Asia. It is one of the eight main cereals in the world. It is well adapted to low rainfall, low soil fertility and high temperatures. This is one of the four most important cereals, which is rich in iron and zinc with high content of antioxidants. It is considered as a staple food among poor people. It is a rich source of carbohydrates, proteins and minerals. (Nambiar et al., 2011)
Protein is mainly present in the aleurone layer of endosperm in the variable amount of 8.6 – 17.4%. The protein content of pearl millet is comparable to the protein content of wheat. The protein content in pearl millet is almost 11.6g/100g, which is higher than rice, sorghum and maize. It is low in lysine, threonine, tryptophan and sulphur containing amino acids. Among the total proteins, prolamins are 33.1 – 49.5% and glutelins are 30.6 – 45.3%. Globulins and albumins together constitute 18 – 26%, with globulins constituting almost 11.6 – 16.8% and albumins constituting 6.4 – 9.6%. The tryptophan content in millet was highest in albumins, glutelins and prolamins and lowest in globulins. Digestibility of amino acids such as lysine, arginine, threonine, valine and isoleucine is higher in pearl millet as compared to other millets. Superior protein quality is because of its tryptophan and threonine content. (Pujar et al., 2020)
Finger Millet (Ragi)
Finger Millet is also known as ragi and is a type of small-sized millet that requires a large area for cultivation and comes under the taxonomic family Poaceae. Because of its high nutritional content, it is considered as a special food supplement. Finger Millet is a great source of calcium along with antioxidants and phytochemicals.
Finger Millet has protein percentage in the range of 4.9 – 11.3%. White finger millet has more protein as compared to brown varieties. Prolamins and glutelins are the main constituents of protein in the finger millet. The essential amino acid level present in this millet is around 44.7%, which is higher than that of 33.9% present in FAO reference protein. Compared to other millets, the nutritional level is balanced in ragi. Eleusinian is the key protein content present in it, which is highly enriched with cystine, tryptophan, methionine and other aromatic amino acids, which are highly helpful for the growth and development of human health, (Shobana et al., 2013). Finger millet has a sufficient amount of tryptophan and threonine, which are deficient in the case of cereals, wheat, rice and sorghum. Moreover, it has a high amount of lysine, valine and threonine and the percentage composition of Sulphur containing amino acids is equal to that of milk. (Jagati et al., 2021)
This is an annual grass plant belonging to the tribe Paniceae of the Poaceae family. It is also known as Italian or German millet and is categorized under small millet due to its small size. It is grown as a staple food in China, India, Myanmar, Russia and Eastern Europe. Foxtail millet contains special proline-rich, alcohol-soluble proteins called setarins constituting almost 60% of millet, containing less amount of disulphide cross-linked proteins.
In foxtail millet, the second most important constituent is protein, followed by carbohydrates, amino acids such as methionine and cysteine, which are predominant among them. Due to the higher protein content, more research and development is ongoing to produce protein concentrates and isolates. Protein fractions in foxtail could be a receptacle of fabricated functional food, like proteins used for the encapsulation of bioactive compounds. Compared to animal proteins, foxtail millet is cheap and sustainable and when combined with other plant-based proteins can give functional and nutritive qualities. Foxtail millet is free from gluten, which provides better health and nutritional properties and they are rich in all essential amino acids, except lysine and tryptophan.
The protein content of foxtail millet is altered by germination, fermentation, dry heat treatment (such as roasting), moist heat treatment (such as extrusion), defatting and protein isolation. The total protein content of whole foxtail seed or rice is dependent on both species, growing conditions and type of processing. The protein content in 14 varieties of foxtail seeds ranged from 11.13 – 18.75%, which is higher than common cereals but lower than pseudocereals, oilseeds and pulses. (Sachdev et al., 2021)
Kodo Millet is also known as cow grass, ditch millet or rice grass and it is a drought-tolerant annual plant, which is cultivated extensively in India, Nepal, Vietnam, Philippines, Indonesia and West Africa. Kodo millet offers an impressive amount of protein, dietary fibre, good fats, calcium and iron. Kodo millet along with sorghum constitute a major source of energy and proteins for millions of people in Asia and Africa.
It has a high protein content of 11%. The prolamine fraction of Kodo millet represents 6.4 – 10.9% of total proteins and the prolamine-like fraction is 4.5 – 9.5% of total protein. The true glutelin fraction form 40.4 – 52.1% of total proteins. The glutelin-like fraction ranges between 7.6 – 9.6% of total protein. The essential amino acids such as isoleucine, leucine, phenylalanine, tryptophan and valine are present in appreciable amounts. Among the non-essential amino acids such as glutamic acids, proline and alanine are also present in large amounts. Whereas, methionine and cystine are present in less than adequate amounts and lysine is highly limiting. The isoleucine: leucine ratio is highly favourable, the leucine: lysine ratio is unfavourable and this is expected to hinder the efficient utilization of lysine which is already severely limiting. Therefore, in Kodo Millet, the overall essential amino acid content is poorly balanced from the nutritional point of view. (Sudharshana et al., 1988)
Barnyard Millet is one of the most significant but underrated minor millet crops that has a great amount of protein, carbohydrates and minerals and has a low glycaemic index with the most number of micronutrients than any other cereal crop. It is a short-duration plant that has a rich source of sulphur-containing amino acids.
Barnyard millet contains almost 11.1 – 13.9% protein. The essential amino acids present in this millet are lysine, methionine, threonine, isoleucine, histidine and tryptophan and the non-essential amino acids are aspartic acid, glutamic acid, arginine, alanine, cysteine, glycine and proline. (Sood et al., 2015)
Proso Millet is the oldest used summer cereal by humans, besides wheat and barley. Nowadays, it is a common food that is mainly consumed in developing countries. In Europe, the grain is usually used as feed for pets. The caryopsis of proso millet is rich in protein, mineral substances and vitamins and its nutritive parameters are better than common cereals.
Prolamin is the most abundant protein component present in proso millet. Millet protein has a beneficial influence on the metabolism of cholesterol. Protein is considered to be another preventive food for liver injury. Proso is a suitable food for patients with gluten-free diets, due to the specific prolamine fraction being under the permitted level. 11.3 – 12.7% is the protein content present in Proso Millet. Proso is a significant source of essential amino acids like leucine and isoleucine. (Kalinova & Moudry, 2006)
Millets are becoming a part of our lives and in the future, we are going to experience new changes in their utilization. The advanced technology, processing methods and research findings show that millet is going to take the position of cereals like rice, wheat, maize, etc. These above mentioned properties are now noticed by food technologists and scientists to make use of them, which can help in ensuring a sustainable future.
The nutritional and functional properties of millet protein are explored by the scientists and more research outputs are being awaited by future society. The higher protein content as well as an excellent aminoacids profile make the millets more popular. Millets will be recognized significantly if the true potential of their nutritive content is promoted around the world.
1. Amadou, I., Gounga, M. E., & Le, G. W. (2013). Millets: Nutritional composition, some health benefits and processing – A review. Emirates Journal of Food and Agriculture, 25(7), 501–508. https://doi.org/10.9755/ejfa.v25i7.12045
2. Chemistry, F. (2015). Seed protein of millets : amino acid composition , proteinase inhibitors and in-vitro protein digestibility Seed protein of millets : amino acid composition , proteinase inhibitors and in-vitro protein digestibility. 44(November), 2–7.
3. Gowda, N. A. N., Siliveru, K., Prasad, P. V. V., Bhatt, Y., Netravati, B. P., & Gurikar, C. (2022). Modern processing of Indian millets: a perspective on changes in nutritional properties. Foods, 11(4), 499.
4. HARDEN, M. L., STANALAND, R., BRILEY, M., & YANG, S. P. (1976). the Nutritional Quality of Proteins in Sorghum. Journal of Food Science, 41(5), 1082–1085. https://doi.org/10.1111/j.1365-2621.1976.tb14392.x
5. Jagati, P., Mahapatra, I., & Dash, D. (2021). Finger millet (Ragi) as an essential dietary supplement with key health benefits: A review. International Journal of Home Science, 7(2), 94–100. https://doi.org/10.22271/23957476.2021.v7.i2b.1152
6. Kalinova, J., & Moudry, J. (2006). Content and quality of protein in proso millet (Panicum miliaceum L.) varieties. Plant Foods for Human Nutrition, 61(1), 43–47.
7. Nambiar, V. S., Dhaduk, J. J., Sareen, N., Shahu, T., & Desai, R. (2011). Potential functional implications of pearl millet (Pennisetum glaucum) in health and disease. Journal of Applied Pharmaceutical Science, 1(10), 62–67.
8. Pontieri, P., & Del Giudice, L. (2015). Sorghum: A Novel and Healthy Food. In Encyclopedia of Food and Health (1st ed.). Elsevier Ltd. https://doi.org/10.1016/B978-0-12-384947-2.00637-1
9. Pujar, M., Gangaprasad, S., Govindaraj, M., Gangurde, S. S., Kanatti, A., & Kudapa, H. (2020). Genome-wide association study uncovers genomic regions associated with grain iron, zinc and protein content in pearl millet. Scientific Reports, 10(1), 1–15. https://doi.org/10.1038/s41598-020-76230-y
10. Sachdev, N., Goomer, S., & Singh, L. R. (2021). Foxtail millet: a potential crop to meet future demand scenario for alternative sustainable protein. Journal of the Science of Food and Agriculture, 101(3), 831–842.
11. Shobana, S., Krishnaswamy, K., Sudha, V., Malleshi, N. G., Anjana, R. M., Palaniappan, L., & Mohan, V. (2013). Finger millet (Ragi, Eleusine coracana L.): a review of its nutritional properties, processing, and plausible health benefits. Advances in Food and Nutrition Research, 69, 1–39.
12. Sood, S., Khulbe, R. K., Gupta, A. K., Agrawal, P. K., Upadhyaya, H. D., & Bhatt, J. C. (2015). Barnyard millet–a potential food and feed crop of future. Plant Breeding, 134(2), 135–147.
13. Sudharshana, L., Monteiro, P. V., & Ramachandra, G. (1988). Studies on the proteins of kodo millet (Paspalum scrobiculatum). Journal of the Science of Food and Agriculture, 42(4), 315–323.
About the Authors:
The views/opinions expressed by authors on this website solely reflect the author(s) and do not necessarily reflect the views/opinions of the Editors/Publisher. Neither the Editors nor the Publisher can be held responsible and liable for consequences that may arise on account of errors/omissions appearing in the Articles/Opinions.