Shankar Senthilkumar, Khumbaron Kiranbala Kabui, K. A. Athmaselvi
Introduction
As the global community tackles the dual challenges of food security and malnutrition, particularly in the face of climate change and population growth, the Sustainable Development Goals (SDGs) set forth by the United Nations emphasize the need for resilient and nutritious food sources. Millets, a group of small-seeded grasses, present a promising solution due to their adaptability to harsh growing conditions and rich nutritional profile. However, the presence of anti-nutritional factors in millets can hinder their full potential. These naturally occurring compounds can reduce the bioavailability of essential nutrients, which poses a significant barrier to improving dietary outcomes in regions that rely heavily on these grains. Millets are vital crops in many parts of Asia and Africa, offering a valuable source of proteins, fiber, vitamins, and minerals. Despite their benefits, the Anti-nutritional Factors present in millet can interfere with nutrient absorption and utilization. This article discusses the anti-nutritional factors in millet and the methods to prevent them.
Anti-nutritional Factors in Millets and Their Impact on Human Metabolism
Millets contain several anti-nutritional factors that can interfere with nutrient absorption, digestion, and utilization. These compounds naturally occur in plants as a defense against pests and diseases but can pose health risks when consumed in significant amounts. The primary anti-nutritional factors found in millets include protease inhibitors, phytates, oxalates, lectins, saponins, and tannins.
Protease Inhibitors
Protease inhibitors reduce the activity of enzymes like trypsin and chymotrypsin, which are essential for breaking down dietary proteins into absorbable amino acids. Inhibiting these enzymes leads to incomplete protein digestion, resulting in fewer amino acids available for absorption, potentially contributing to protein malnutrition (Chandrasekher et al., 1982).
Phytates:
Phytates, or phytic acid, chelate essential minerals such as calcium, iron, and zinc, forming insoluble complexes that the body cannot absorb. Calcium is important for bone mineralization, muscle contraction, nerve transmission, and blood clotting. Iron is essential for hemoglobin production, which transports oxygen in the blood, and for various enzymatic reactions. Zinc is involved in numerous aspects of cellular metabolism, including DNA synthesis, immune function, and protein synthesis (Meka, 2021).
Oxalates:
Oxalates bind with calcium to form calcium oxalate, an insoluble compound that precipitates out in the kidneys, forming kidney stones. The formation of calcium oxalate reduces the amount of free calcium available for absorption, impacting bone health and neuromuscular function (Franceschi & Nakata, 2005).
Lectins:
Lectins bind to carbohydrates on the surfaces of intestinal epithelial cells, disrupting the tight junctions that maintain the integrity of the gut barrier. This can lead to increased intestinal permeability and inflammation, complicating nutrient absorption.
Saponins
Saponins interact with cholesterol in cell membranes, forming complexes that disrupt membrane integrity and increase permeability. This affects processes such as nutrient absorption, ion transport, and cell signaling, potentially leading to digestive issues (Mishra et al., 2019).
Tannins:
Tannins bind to dietary proteins and digestive enzymes, forming insoluble complexes that precipitate and are not absorbable. This binding reduces the digestibility of proteins, making them less available for absorption in the intestines (Meka, 2021).
Reducing these anti-nutritional factors can enhance the bioavailability of nutrients, ensuring they are available for absorption and utilization in the body. Effective management of these factors is crucial for maximizing the nutritional benefits of millets.
Methods to Reduce Anti-Nutritional Factors
Soaking and Germination
Soaking is one of the simplest and most effective methods to reduce anti-nutritional factors, particularly phytates and tannins. The process involves soaking the seeds in water for a specified period, which initiates germination. During germination, endogenous enzymes such as phytase are activated. These enzymes break down phytates into inositol and inorganic phosphate, thereby reducing their anti-nutritional effect. Soaking also helps leach out water-soluble tannins, further enhancing the nutritional value of millet. Germination not only reduces Anti-nutritional Factors but also increases the bioavailability of nutrients. For example, germinated millet seeds have higher levels of bioavailable iron and zinc compared to ungerminated seeds. The process also enhances the content of certain vitamins, such as vitamin C, which can further aid in iron absorption (Patiballa et al., 2024).
Fermentation
Fermentation is another effective method to reduce anti-nutritional factors, especially phytates. Lactic acid fermentation, a traditional method used in many cultures, involves the use of beneficial bacteria to ferment millet seeds. This process lowers the pH of the food, which in turn activates endogenous phytase and enhances the breakdown of phytates. Fermentation also increases the bioavailability of minerals and improves the sensory qualities of millet-based foods. Fermented millet products, such as traditional African and Indian dishes, are known to have reduced levels of phytates and tannins. The process also enhances the protein digestibility of millets by breaking down protease inhibitors. Moreover, fermentation can produce beneficial compounds like probiotics, which contribute to gut health (Anyiam et al., 2023).
Heat Treatment
Heat treatment methods, such as boiling, steaming, and roasting, are widely used to reduce the levels of protease inhibitors and tannins in millet. Boiling and steaming can denature protease inhibitors, making them inactive and thus improving protein digestibility. Roasting, on the other hand, can reduce the levels of tannins and other phenolic compounds. However, it is necessary to control the conditions of heat treatment to prevent the degradation of essential nutrients.
Excessive heat can lead to the loss of vitamins and other heat-sensitive compounds. Therefore, controlled heat treatment is essential to achieve the desired reduction in Anti-nutritional Factors without compromising the nutritional quality of millet (Jaichand et al., 2020).
Enzymatic Treatment
Enzymatic treatment involves the application of specific enzymes to break down Anti-nutritional Factors in millets. For example, adding phytase to millet-based foods can hydrolyze phytates into inositol and inorganic phosphate, reducing their anti-nutritional effect. Similarly, proteolytic enzymes can be used to degrade protease inhibitors, improving protein digestibility. Enzymatic treatment can be particularly effective when combined with other methods, such as soaking and fermentation. For instance, adding phytase during the fermentation process can further enhance the breakdown of phytates. This method is especially useful in industrial food processing, where controlled conditions can be maintained to achieve consistent results (Adeyemo & Onilude, 2013).
Breeding and Genetic Modification
Advances in breeding techniques and genetic modification can help in developing millet varieties with lower levels of Anti-nutritional Factors. Conventional breeding methods involve selecting and crossbreeding millet varieties with naturally low levels of Anti-nutritional Factors. Over time, this can lead to the development of new varieties that are more nutritionally beneficial. Genetic modification offers more precise control over the levels of anti-nutritional factors in millets. This approach can also be used to enhance beneficial nutrients, further improving the nutritional profile of millet (Duraiswamy et al., 2023).
Conclusion
Millets are a valuable source of nutrients and hold great potential for improving global food security. However, their nutritional benefits are limited by the presence of anti-nutritional factors. While these factors are often seen as barriers to nutrient absorption, they can offer significant health benefits when managed properly. Advances in processing techniques, breeding, and genetic modification can help improve the nutritional profile of millets, making them a viable option for addressing global nutrition challenges. Further research and development in these areas will be crucial for maximizing the potential of millets in sustainable food systems.
Author’s Bio
Center for Excellence in Grain Sciences, National Institute of Food Technology, Entrepreneurship and Management -Thanjavur-613005, India
References
Adeyemo, S. M., & Onilude, A. A. (2013). Enzymatic Reduction of Anti-nutritional Factors in Fermenting Soybeans by Lactobacillus plantarum Isolates from Fermenting Cereals. Nigerian Food Journal, 31(2), 84–90. https://doi.org/10.1016/S0189-7241(15)30080-1
Anyiam, P. N., Nwuke, C. P., Uhuo, E. N., Ije, U. E., Salvador, E. M., Mahumbi, B. M., & Boyiako, B. H. (2023). Effect of fermentation time on nutritional, antinutritional factors and in-vitro protein digestibility of macrotermes nigeriensis-cassava mahewu. Measurement: Food, 11, 100096. https://doi.org/10.1016/j.meafoo.2023.100096
Chandrasekher, G., Raju, D. S., & Pattabiraman, T. N. (1982). Natural plant enzyme inhibitors. Protease inhibitors in millets. Journal of the Science of Food and Agriculture, 33(5), 447–450. https://doi.org/10.1002/jsfa.2740330509
Duraiswamy, A., Sneha A., N. M., Jebakani K., S., Selvaraj, S., Pramitha J., L., Selvaraj, R., Petchiammal K., I., Kather Sheriff, S., Thinakaran, J., Rathinamoorthy, S., & Kumar P., R. (2023). Genetic manipulation of anti-nutritional factors in major crops for a sustainable diet in the future. Frontiers in Plant Science, 13. https://doi.org/10.3389/fpls.2022.1070398
Franceschi, V. R., & Nakata, P. A. (2005). CALCIUM OXALATE IN PLANTS: Formation and Function. Annual Review of Plant Biology, 56(1), 41–71. https://doi.org/10.1146/annurev.arplant.56.032604.144106
Jaichand, V., Dwarka, D., Gerrano, A. S., & Mellem, J. J. (2020). Effect of heat processing on the nutritional and anti-nutritional factors of cowpea (Vigna unguiculata). The Annals of the University Dunarea de Jos of Galati Fascicle VI – Food Technology, 44(1), 165–177. https://doi.org/10.35219/foodtechnology.2020.1.10
Meka, W. (2021). Antinutritional Factors in Plants, Potential Application and its Adverse Effect. In Journal Nutraceuticals and Food Science (Vol. 6, Issue 11). www.imedpub.com
Mishra, A., Behura, A., Mawatwal, S., Kumar, A., Naik, L., Mohanty, S. S., Manna, D., Dokania, P., Mishra, A., Patra, S. K., & Dhiman, R. (2019). Structure-function and application of plant lectins in disease biology and immunity. Food and Chemical Toxicology, 134, 110827. https://doi.org/10.1016/j.fct.2019.110827
Patiballa, M., Ravindra, U., Benherlal P. S., Subbarayappa, C. T., Shivakumar, N., Mamatha H. S., & Vijayalaxmi, K. G. (2024). Effect of Soaking and Germination on Antinutritional Factors of Quinoa (Chenopodium quinoa). International Journal of Plant & Soil Science, 36(1), 120–130. https://doi.org/10.9734/ijpss/2024/v36i14337
