How to Diversify Food Systems with Broccoli Microgreens

Current malnourishment statistics are high and are exacerbated by contemporary agricultural practices that damage the very environments on which the production of nutritious food depends. As the World's population grows at an unprecedented rate, food systems must be revised to provide adequate nutrition while minimizing environmental impacts. One specific nutritional problem that needs attention is mineral (e.g., Fe and Zn) malnutrition, which impacts over two-thirds of the World's people living in countries of every economic status. Microgreens, the edible cotyledons of many vegetables, herbs, and flowers, is a newly emerging crop that may be a dense source of nutrition and has the potential to be produced in just about any locale. This study examined the mineral concentration of broccoli microgreens produced using compost-based and hydroponic growing methods that are easily implemented in one's own home. The nutritional value of the resulting microgreens was quantitatively compared to published nutritional data for the mature vegetable. Nutritional data were also considered in the context of the resource demands (i.e., water, fertilizer, and energy) of producing microgreens in order to gain insights into the potential for local microgreen production to diversify food systems, particularly for urban areas, while minimizing the overall environmental impacts of broccoli farming. Regardless of how they were grown, microgreens had larger quantities of Mg, Mn, Cu, and Zn than the vegetable. However, compost-grown (C) microgreens had higher P, K, Mg, Mn, Zn, Fe, Ca, Na, and Cu concentrations than the vegetable. For eight nutritionally important minerals (P, K, Ca, Mg, Mn, Fe, Zn, and Na), the average C microgreen:vegetable nutrient ratio was 1.73. Extrapolation from experimental data presented here indicates that broccoli microgreens would require 158-236 times less water than it does to grow a nutritionally equivalent amount of mature vegetable in the fields of California's Central Valley in 93-95% less time and without the need for fertilizer, pesticides, or energy-demanding transport from farm to table. The results of this study suggest that broccoli microgreens have the potential to be a rich source of minerals that can be produced by individuals, even in urban settings, providing better access to adequate nutrition.

Introduction:

The strong dependence of human nutrition on the environmental sustainability of crop production has come into focus as problem-solving efforts work to identify mechanisms to feed the World’s rapidly growing population (1). Current malnourishment statistics are high and contemporary agricultural practices are a dominant force in damaging the very environments on which the production of nutritious food depends (1, 2). In the U.S., food production utilizes 50% of land and is responsible for 80% of total freshwater consumption (3), which occurs at a rate that is faster than aquifer recharge in some regions. Food production also depends heavily of fertilizer and pesticide application, which is adversely impacting ecosystem biodiversity (2). Additionally, cultivation is increasingly focused on the mass production of fewer staple crops. This reduces the nutritional value of the average diet and makes food production less resilient to environmental change (4, 5), should it be the demise of one or more of these relatively few crops. Therefore, simply upscaling current agricultural practices to increase crop yields is not a viable solution for feeding the World’s population. It is a priority to establish dietary guidelines that satisfy human nutritional requirements with a diversity of foods that can be produced with minimized environmental impact (6–8); this is key to ensuring socioeconomic and sociocultural prosperity into the future (2).

Achieving such developments requires revising food systems. Food systems are comprised of not only activities associated with food production but also those associated with food processing, transport, consumption, and governance of the above named. In addition to the flaws in food production methods discussed above, 40% of the food produced is never consumed, comprises the largest component of municipal waste, and is responsible for a large fraction of annual methane emissions in the U.S. (3). Much of this food is transported over long distances from farms to urban centers, which consumes 10% of the total energy budget in the U.S. (3) and contributes to food waste as it spoils or is contaminated enroute (2). Reliance on these long food chains threatens food security in urban areas, where over 54% of the World’s population is concentrated (9), as it puts sustenance for their populations at the mercy of natural and anthropogenic disasters in distant locations. The collective makes current food systems vulnerable to the environmental changes they also contribute to.

With respect to nutrition, the flaws in food systems create a dichotomous problem of excess and insufficiency. This is exemplified by one-third of the world’s people being overweight and/or undernourished (2, 8, 10). This problem impacts countries of every economic status (10). The reliance of urban populations on long food chains limits accessibility to produce that has short shelf lives and, therefore, poor transportability, and increases dependence on heavily processed and packaged foods; this creates “food deserts” in urban areas in which people do not have ready access to a complete compliment of required nutrients (11). However, even the fresh produce that does reach its destination has likely lost substantial nutritional value during transport (12).

One specific nutritional problem that is common in developed and developing countries is mineral malnutrition. Over 60, 30, and 15% of the World’s seven billion people are Fe-, Zn-, and Se-deficient, respectively (13). Rates of mineral malnutrition are especially high in Asia and Africa (14), where soil degradation is especially severe and has significantly decreased the nutritional value of crops (15). However, mineral malnutrition is considered to be one of the most important global challenges to mankind that can be prevented (16) and is one of the Millennium Development Goals (14). Current efforts to mitigate mineral malnourishment are focused on developing biofortification methods (13) and genetically engineering crops for maximal nutrient uptake (17).

However, a newly emerging crop that may be a dense source of nutrition in the absence of biofortification and genetic engineering and has the potential to be produced in just about any locale is microgreens. Microgreens are edible seedlings that are usually harvested 7–14 days after germination when they have two fully developed cotyledon leaves (18). A wide variety of herbs (e.g., basil, cilantro), vegetables (e.g., radish, broccoli, and mesclun) and even flowers (e.g., sunflowers) are grown as microgreens. Microgreens are generally more flavorful, some of them quite spicy, than their mature counterparts and have grown in popularity among culinary artists for adding texture and flavor accents to salads, sandwiches, and other dishes (19, 20). The increasing culinary demand as well as the ease with which microgreens can be grown, even by inexperienced gardeners in urban settings, has piqued interests in growing and eating them. Interest in microgreens has also been generated by popular websites (21) touting the findings of Xiao et al. (18), which indicate that microgreens may have 4–40 times the amount of some nutrients and vitamins as the vegetables a mature plant would produce. However, Xiao et al. (18) note that the nutritional aspects they measured varied widely among microgreen types, providing fodder for future study. Additionally, Weber (22) noted that the methods used to grow microgreens (i.e., soil, compost, hydroponic) can significantly impact their nutritional value. A systematic comparison of the environmental impacts (i.e., water use, nutrient demand) of microgreen cultivation methods has not been conducted and should be considered alongside their impacts on nutritional value when deciding how to grow microgreens and if they are a nutrient-rich crop that can be sustainably produced.

In this study, the mineral concentration was determined for broccoli microgreens that had been grown hydroponically or using compost-based methods that are easily implemented by the average citizen. The nutritional value of the resulting microgreens was quantitatively compared to that of mature broccoli florets. In order to gain insights into the potential of local microgreen production to sustainably diversify food systems, particularly for urban areas, the nutritional value of microgreens was considered in the context of the resource demands (i.e., water, fertilizer, and energy inputs) of producing them relative to those of producing mature broccoli vegetable in California’s Central Valley.