The Science behind Microgreens
Microgreens are a new generation of foods.
It's been quite common to have seen microgreens used only in high-end restaurants as garnish and to embellish culinary dishes, however recent studies demonstrate microgreens are a rising and important food source of nutrition for the overall and complete human diet.
Initially, microgreens were used in cooking as colorful vegetables which were appreciated for their lively embellishment of culinary dishes. Today, we use them for improving the nutritional value of the human diet, since they are naturally rich in macro and micronutrients, carotenoids, vitamin C, E, and K1, as well as phenolic compounds.
Some studies have now highlighted their nutritional potential compared to their mature counterparts. Studies comparing lettuce, harvested at the microgreen stage have shown to possess a greater nutraceutical content than the mature lettuce. Researchers also saw higher levels of calcium, magnesium, total polyphenol content and a higher content of antioxidant molecules compared to their mature counterparts.
As such, microgreens are defined as super-foods for their content of vitamins E, C, and K, carotenoids (β-carotene, lutein, and zeaxanthin), and their antioxidant activity which are almost ten times greater than that of mature leafy vegetables. The advantage of microgreens is that they are eaten raw, so they maintain thermolabile vitamins, such as vitamin C. If cooked, vitamin C completely loses its nutritional value.
Microgreens are also considered functional foods due to their high polyphenol content and because they are considered rich sources of minerals. These make possible the proper regulating of cell homeostasis and metabolism in the human body, and to serve as co-factors for several enzymes.
Among 5 of the microgreen species of the Brassicaceae (namely broccoli, daikon, mustard, rocket salad, and watercress), broccoli had the highest polyphenol, carotenoid, and chlorophyll contents, as well as strong antioxidant power. Microgreen Brassica vegetables of broccoli, kale, and radish are also shown to be good sources of health-promoting phytochemicals with high antioxidant capacities.
With respect to minerals, microgreens contain various minerals important to human health, with some minerals higher in microgreens than mature counterparts, including selenium, copper, iron, zinc, and molybdenum.
The higher concentration of minerals in microgreens in some cases represents their potential in helping increase mineral intake, particularly for minerals where deficiency is more common globally (e.g. iron, zinc, and selenium).
Besides macro and microelements, vitamins, polyphenols, and other bioactive compounds, dietary fiber (DF) is another essential component of the human diet. The macromolecules of DF mainly consist of plant cell wall components, polysaccharides, and lignin. They resist digestion by endogenous enzymes in the human gut and promote the satiety sensation. The health benefits of DF include weight loss, prevention and treatment of constipation, control of serum cholesterol levels, and improved glucose tolerance, among others. In addition, the ability of DF to bind toxic compounds has been recognized as a protective mechanism against cancer.
All microgreen crops are moderate to good sources of protein, dietary fiber, and essential nutrients. Concerning their vitamin content, the studied microgreens are excellent sources of ascorbic acid, vitamin E, and beta-carotene (pro-vitamin A), meeting 28–116%, 28–332%, and 24–72% of reference daily intake of the respective vitamins. In general, microgreens had low levels of oxalic acid, which is a predominant anti-nutrient in mature leafy vegetables.
Ascorbic acid content is often higher at the adult stage than the microgreen stage and the human body cannot appropriately benefit from this rich ascorbic acid source. Leafy vegetables at the mature stage are generally consumed after cooking, and ascorbic acid is known to be easily destroyed by heat. In contrast, microgreens are usually consumed fresh; hence, the human body can fully benefit from this ascorbic acid source in microgreens.
The examples in this section indicate that microscale vegetables are, in general, nutrient-dense and rich in phytochemicals, often with a reduced level of antinutrients as compared to the adult growth stage, hence constituting an attractive component as a functional food in the diet of health-conscious consumers.
Healthy diets are essential for nutrition and health and a healthy diet is one that is health-promoting and disease-preventing. About three billion people cannot afford healthy diets around the globe. The triple burden of malnutrition, i.e., undernutrition, micronutrient deficiency, and overnutrition, affects most nations around the globe. As incomes rise and food consumption patterns change, overnutrition from imbalanced diets increasingly becomes a concern in developed and developing countries.
Malnutrition is a high-risk factor for non-communicable diseases (NCDs), also known as chronic diseases. Diet-related NCDs, such as diabetes, cardiovascular disease, hypertension, stroke, cancer, and obesity, are escalating globally. Out of the estimated 40.5 million people killed by NCDs each year (71% of the annual deaths worldwide), approximately 32.2 million NCD deaths (80%) were attributable to cancers, cardiovascular diseases, chronic respiratory diseases, and diabetes.
Microgreens were found to have an extensive and diverse range of metabolites (including vitamins and bioactive compounds) and minerals, providing further evidence for their high nutritional quality. We found that several, but not all, metabolites and minerals were higher in microgreens compared with the mature counterparts. We also found that each microgreen species had numerous metabolites that were unique to that species.
Researchers found that microgreens are concentrated sources of metabolites, namely bioactive compounds, and in many cases more concentrated than the mature counterpart and is of relevance to human nutrition and health and necessitates further investigation. Microgreen consumption could increase plant bioactive compound intake beyond usual intake to achieve specific functional health effects. An important area of consideration is the bioaccessibility (the quantity or fraction released from the food matrix in the gastrointestinal tract for absorption) and bioavailability (the fraction of ingested nutrient/compound that reaches systemic circulation and is utilized) of the compounds. Ascorbic acid (vitamin C) and bioactive compounds including carotenoids, isothiocyanates, and polyphenols in Brassicaceae microgreens were shown to be bioaccessible through simulated gastrointestinal in vitro digestion, but this was significantly impacted by plant genotype. Furthermore, as microgreens are usually consumed raw, there is hardly a loss or degradation of heat-sensitive micronutrients or vitamins through food processing.
Sources:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9695664/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8877763/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7897203/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5362588/