Microgreens are the young leaves of plants from different plant families, frequently used as salad greens and herbs. Microgreens is an umbrella term that includes ‘shoots’, the stage from 7 to 14 days, and ‘microgreens’ or ‘baby’ from 14 to 21 days. Microgreens contain higher amounts of phytonutrients and minerals and lower nitrate than their mature counterparts, and the vitamin content can be many times that of the mature plants. The metabolic changes that take place during germination increase the bioavailability of essential nutrients in microgreens compared to the mature plants. Also, it is easier to include the small amount of microgreens into the diet than the equivalent amount of mature vegetables. The role of phytonutrients in plant growth is described below, explaining why microgreens are so nutritious.
Seed germination is not the very beginning of plant generation, it is the awakening from a dormant phase where development was arrested. Development stopped when the seed coat cut off the water supply from the parent plant, it restarts when water soaks through the seed coat and reaches the embryo. Once sprouts emerge from the seed, they rapidly develop cell bodies that contain chlorophyll (chloroplasts) and begin to photosynthesize.
During germination, from the moment the seed breaks dormancy, various plant compounds are formed. Polyphenols are synthesized and they act to protect the plant against environmental factors and to provide structure for growth. Antioxidants play an important role in seed dormancy, breakage and germination. Antioxidants synthesized during germination are essential to the protection of the new seedling by inhibiting the damage of cell membranes. Micronutrients like minerals are integral to cellular function in plants, such as activating enzymes and stabilizing proteins.
Antioxidants are classes of compounds that can safely interact with free radicals and end a chain reaction before vital molecules are damaged. The major classes of these compounds include: vitamins (C and E), carotenoids, and polyphenols (flavonoids, phenolic acids, stilbenes, lignans). Antioxidants act in living cells, help protect plants from environmental stresses and modulate plant growth. The concentrations of the antioxidants beta-carotene, ascorbic acid, tocopherols and phenolic acids increase along with the length of germination until they plateau when the true leaves have emerged (after 21 days).
Ascorbic acid (vitamin C) is important in plant growth and during germination the respiration process is triggered by ascorbic acid. Carotenoids are synthesized and stored in the cell areas where they act as additional pigments to chlorophylls in photosynthesis. Tocopherols protect plant tissues from structural damage during germination and early seedling development, tocopherols also protect plant cells from stress conditions.
Brightly coloured fruits and vegetables are usually high in nutritional value, and these colours derive from plant compounds involved in growth and development. Flavonoids are a type of polyphenol that act to defend the plant from ultraviolet radiation and pathogens. Anthocyanins are natural pigments and a type of flavonoid, and they are responsible for conferring bright colours to plant tissues. Anthocyanin accumulation in plant tissues is related to light exposure, as light is required for its’ synthesis. Fruit and vegetables with high levels of flavonoids also have high total antioxidant activity.
Isothiocyanates are bioactive compounds found in plant structures. Sulforaphane is an isothiocyanate that has been the subject of much scientific interest due to its’ potential role in cancer prevention. Research into the Brassica family found many species to be high in sulforaphane, and in particular the shoots of broccoli, kale and cabbage contain 10 to 100 times more sulforaphane than that of the mature plant. The potent phytonutrients that interest scientists and consumers for their potential in cancer prevention are the same factors that cause the strong taste in broccoli shoots, cabbage and kale shoots.
Plants require essential nutrients and minerals in the life cycle. Calcium has a pivotal role in plant growth and development, and the response to internal and external signals. Magnesium has an essential role in photosynthesis. Nitrogen is important for internal regulation and the development of chemical compounds integral to the plant life cycle. Phosphorus is needed in cell metabolism, such as embryo development, germination and seedling growth. Potassium has an important role in protein synthesis, activating enzymes and cell function. Iron performs multiple roles in photosynthesis, respiration, hormone synthesis and defense against pathogens. Zinc is important in protein synthesis, energy production, plant structure, and seed development.
There can be wide variation in the vitamin content and micro and macro elements in microgreens depending on the growing conditions, natural variability between different varieties of the same species, and pre-harvest and post-harvest conditions. Recent research demonstrated that broccoli shoots grown in compost using organic methods had higher concentrations of several essential minerals than did shoots grown hydroponically with or without fertilizer. The seed contains enough nutrients for plant growth to the shoot stage, which makes fertilizer use redundant. For consumers, storing microgreens at the correct temperature (about 4C) is important for maintaining optimal nutrition and shelf life.
There is potential for the expansion of microgreen production to reduce the environmental footprint of industrial agriculture. For example, industrial broccoli farming takes 100 to 150 days in a temperate climate like central California and uses 2.4 to 3.7 million litres of water annually. Growing broccoli shoots takes 7 – 9 days and uses 158 to 236 times less water than a nutritionally equivalent amount of mature broccoli. Home-based production of microgreens could help reduce agricultural impact by reducing water use, fertilizers, pesticides, and fossil fuels. Workshops to learn about growing microgreens are available, and supplies are commercially available. Dawn has offered workshops previously, and will continue in the future. She recently conducted a season extension webinar for Alberta Agriculture and Forestry which can be found on their website.
Bains, K., Uppal, V., & Kaur, H. (2014). Optimization of germination time and heat treatments for enhanced availability of minerals from leguminous sprouts. Journal of food science and technology, 51(5), 1016-1020.
Fahey, J. W., Zhang, Y., & Talalay, P. (1997). Broccoli sprouts: an exceptionally rich source of inducers of enzymes that protect against chemical carcinogens. Proceedings of the National Academy of Sciences, 94(19), 10367-10372.
Guzman, I., Yousef, G. G., & Brown, A. F. (2012). Simultaneous extraction and quantitation of carotenoids, chlorophylls, and tocopherols in Brassica vegetables. Journal of agricultural and food chemistry, 60(29), 7238-7244.
Hänsch, R., & Mendel, R. R. (2009). Physiological functions of mineral micronutrients (Cu, Zn, Mn, Fe, Ni, Mo, B, Cl). Current opinion in plant biology, 12(3), 259-266.
Kyriacou, M. C., Rouphael, Y., Di Gioia, F., Kyratzis, A., Serio, F., Renna, M., … & Santamaria, P. (2016). Micro-scale vegetable production and the rise of microgreens. Trends in Food Science & Technology, 57, 103-115.
Maathuis, F. J. (2009). Physiological functions of mineral macronutrients. Current opinion in plant biology, 12(3), 250-258.
Mir, S. A., Shah, M. A., & Mir, M. M. (2017). Microgreens: Production, shelf life, and bioactive components. Critical reviews in food science and nutrition, 57(12), 2730-2736.
Moral, L., Perez-Vich, B., Velasco, L. (2015). Tocopherols in sunflower seedlings under light and dark conditions. The Scientific World Journal.
Oroian, M., & Escriche, I. (2015). Antioxidants: characterization, natural sources, extraction and analysis. Food Research International, 74, 10-36.
Pinto, E., Almeida, A. A., Aguiar, A. A., & Ferreira, I. M. (2015). Comparison between the mineral profile and nitrate content of microgreens and mature lettuces. Journal of Food Composition and Analysis, 37, 38-43.
Qian, H., Liu, T., Deng, M., Miao, H., Cai, C., Shen, W., & Wang, Q. (2016). Effects of light quality on main health-promoting compounds and antioxidant capacity of Chinese kale sprouts. Food chemistry, 196, 1232-1238.
Xiao, Z., Codling, E. E., Luo, Y., Nou, X., Lester, G. E., & Wang, Q. (2016). Microgreens of Brassicaceae: Mineral composition and content of 30 varieties. Journal of Food Composition and Analysis, 49, 87-93.
Xiao, Z., Lester, G. E., Luo, Y., & Wang, Q. (2012). Assessment of vitamin and carotenoid concentrations of emerging food products: edible microgreens. Journal of agricultural and food chemistry, 60(31), 7644-7651.
Weber, C. F. (2017). Broccoli microgreens: a mineral-rich crop that can diversify food systems. Frontiers in nutrition, 4, 7.