In a recent review published in the journal Heliyon, researchers at the ICAR-National Bureau of Plant Genetic Resources, New Delhi, collated and synthesized available literature on microgreens, the nutrient-rich seedlings of herbs and vegetables. They elucidate the history and evolution of microgreens, their optimal cultivation methods, nutritional content, biochemistry, commercial significance, and health benefits. They further touch upon challenges and gaps in our understanding of these "desert foods" to inform future cultivators and researchers on the best practices to subscribe to when utilizing microgreens.
What are microgreens?
Following shifting trends in general health, most notably the introduction and increasing adoption of the suboptimal Western diet, a global inadequacy in vitamins and minerals has been observed. When combined with the growing human population and climate-change-mediated reductions in conventional agricultural production, a need arises for novel functional foods characterized by short turnover times, drought resistance, and the convenience of urban farming (vertical farms, hydroponics, greenhouses, and aquaponics).
As a conflux of medical, nutritional, and biological knowledge, microgreens are one such innovative functional food. 'Microgreens' is the colloquial term for the young seedlings of edible vegetables and herbs that have not yet developed cotyledonary leaves. Research has revealed that these plants have nutritional content equal to or exceeding 40 times their adult (mature vegetable) counterparts. When combined with their validated health and beauty benefits, cultivation versatility and resilience, and positive environmental impacts, microgreens are gaining substantial interest as the food of the future.
"Since microgreens are a relatively new specialty food, there is not yet a large body of study on their nutritional content and health benefits."
The evolution of microgreens
While the term 'microgreens' is relatively novel, the practice of consuming unripe vegetables has been prevalent for decades. Some authors attribute the advent of modern microgreens to chefs' gardens during the 1980s in the United States of America (US), where vegetables were grown, shipped, and consumed in their immature state. This practice was further popularized by trendy eateries that targeted the fitness and health-conscious when marketing microgreens as more nutritious than their mature counterparts.
Surprisingly, despite microgreens existing since before the coining of the term "functional foods" (year 2000), a standard definition of these foods and the plant species that comprise them remains elusive. The current review synthesizes an amalgamation of numerous studies' definitions as follows:
"…microgreens can be described as the germinations of seeds that have fully grown genuine leaves and non-senescent cotyledons, but are removed before the development of roots."
Mass microgreen production
Microgreens present far more cultivation versatility than their adult forms. Despite predominantly being grown in controlled greenhouse environments, these foods can be cultivated in any setting with stable temperature (< 20 °C) and humidity. Microgreens also require much less human labor and space than conventional crops – three of four individuals are sufficient to produce more than 90 kg of microgreens per week in an area of only 400 m2. Fast-growing microgreen species can yield harvest in as little as 10 to 14 days.
Pest management and humidity regulation are the most essential variables impacting microgreen yield. While these plants are susceptible to the same pests and pathogens as their older counterparts, short turnover times and intrinsic bioactive metabolites minimize these effects. In some cases, biopesticides and bacterial treatments have proven successful in preventing losses. The recent shift from manual to machine-controlled humidity regulation and harvesting further improves microgreen yields in commercial facilities.
Why are microgreens more nutritious than adult plants?
Research has revealed that dormant dry seeds undergo significant biochemical and nutritional changes (accumulation, remobilization, and disintegration) once their germination is initiated. These processes result in a 'condensing' of nutrients within edible plant parts, contributing to microgreens' surprisingly high nutrient content.
In addition, comparisons between germinating and non-germinating seeds and adult plants have shown that the primary and secondary metabolite compositions of germinating seeds significantly differ from the other two cohorts. Consequently, some varieties of microgreens contain nutrients unobtainable from adult crops.
Health benefits of microgreens
Microgreens are rich sources of carbohydrates, proteins, lipids, vitamins, minerals, and phytochemicals. Clinical and case-control trials have revealed the significant antioxidant potential of these foods and have elucidated their medical potential in controlling (decreasing) blood glucose, weight management, and reducing cardiovascular disease (CVD) risk. Phytochemical components of microgreens are readily digestible and are hypothesized to have antibacterial, anti-diabetic, and anti-inflammatory effects.
Notably, microgreens from broccoli, radish, and other Brassicaceae representatives contain phytochemicals such as indoles and flavonoids with proven anti-cancer efficacy against colorectal cancer. Further research is required to investigate if these properties extend to other cancers and microgreen species.
Challenges associated with microgreen production
The main challenge of the microgreen industry is storage – these foods have an especially short shelf life with a rapid reduction in nutritional content during storage. An additional challenge is that of initial investment – commercial microgreen facilities require expensive and specialized substrates, seeds, machinery, and labor.
The future
"In moving forward, well-designed clinical trials are essential to comprehensively elucidate the impact of microgreens on human health, providing concrete evidence for their health-improving effects. As the exploration of microgreens continues, their promising attributes position them as a valuable subject of study, offering a potential avenue for future advancements in preventive and therapeutic medicine."