Scientific Data on Microgreens Nutrition

First of all, a Definition of Microgreens:

• USDA -- '“Microgreens” is a marketing term used to describe tiny, tender, edible greens that germinate in soil or a soil substitute from the seeds of vegetables and herbs. Smaller than “baby greens,” and harvested later than “sprouts,” microgreens can provide a variety of leaf flavors, such as sweet and spicy. They are also known for their various colors and textures." https://agresearchmag.ars.usda.gov/2014/jan/greens paraphrased/summarized from this study: https://pubag.nal.usda.gov/catalog/59409 -- PDF here: https://pubag.nal.usda.gov/download/59409/PDF
• Xiao -- "Microgreens are tender immature greens produced from the seeds of vegetables and herbs, having two fully developed cotyledon leaves with or without the emergence of a rudimentary pair of first true leaves. Microgreens are usually 2.5−7.6 cm (1−3 in.) in height, harvested at 7−14 days after germination, depending on the species, and sold with the stem and attached cotyledons (seed leaves). Although small in size, microgreens can provide a large array of intense flavors, vivid colors and tender textures."

Nutritional Advantage of Microgreens over Fully-Grown counterparts:

• From the abstract of the premier study of nutrition in microgreens--Assessment of Vitamin and Carotenoid Concentrations of Emerging Food Products: Edible Microgreens; Zhenlei Xiao, et. al. Link: https://pubag.nal.usda.gov/download/59409/PDF 

"The present study was conducted to determine the concentrations of ascorbic acid, carotenoids, phylloquinone, and tocopherols in 25 commercially available microgreens. Results showed that different microgreens provided extremely varying amounts of vitamins and carotenoids. Total ascorbic acid contents ranged from 20.4 to147.0 mg per 100 g fresh weight (FW), while β-carotene, lutein/zeaxanthin, and violaxanthin concentrations ranged from 0.6 to 12.1, 1.3 to 10.1, and 0.9 to 7.7 mg/100 g FW, respectively. Phylloquinone level varied from 0.6 to 4.1 μg/g FW; meanwhile, α-tocopherol and γ- tocopherol ranged from 4.9 to 87.4 and 3.0 to 39.4 mg/100 g FW, respectively. Among the 25 microgreens assayed, red cabbage, cilantro, garnet amaranth, and green daikon radish had the highest concentrations of ascorbic acids, carotenoids, phylloquinone, and tocopherols, respectively. In comparison with nutritional concentrations in mature leaves (USDA National Nutrient Database), the microgreen cotyledon leaves possessed higher nutritional densities. The phytonutrient data may provide a scientific basis for evaluating nutritional values of microgreens and contribute to food composition database. These data also may be used as a reference for health agencies’ recommendations and consumers’ choices of fresh vegetables."

Other Take-aways from the Xiao study:

• Epidemiological studies have shown that fruit and vegetable consumption is associated with reduction in the development of chronic disease, such as cancer and cardiovascular disease.1,2 Diets rich in fruits and vegetables provide an abundance of human bioactive compounds,3 such as ascorbic acid (vitamin C), carotenoids (provitamin A compounds), phylloquinone (vitamin K1), and tocopherols (vitamin E), which are known to have protective benefits against cancers and cardiovascular disease.4 
• Samples were harvested without roots, packed in clamshell containers (113.4 g of each) and shipped overnight in a cardboard box which was filled with frozen-ice packs. When received, 3 g of fresh tissue was weighed for ascorbic acid analysis. Remaining tissue was frozen in liquid nitrogen and lyophilized for dry weight and other vitamin and carotenoid determinations. NOTE: This means the results were probably affected by the plants having already been harvested a day earlier.
• Red cabbage microgreens contained an average of 11.5 mg/100 g FW which is approximately 260-fold more than the value (0.044 mg/100 g FW) reported for mature red cabbage leaves.17 NOTE: This is the source of the 200 times nutritional value number often seen on internet articles--it’s actually 260 times!--and refers to carotenoids (which is “an important fat-soluble antioxidant and can protect cellular membranes by scavenging free radicals.17”)
• In summary, the essential vitamin and carotenoid concen- trations of 25 commercially available microgreens varieties have been determined. In general, microgreens contain considerably higher concentrations of vitamins and carotenoids than their mature plant counterparts, although large variations were found among the 25 species tested. Maximum values of vitamin C, viamin K1, and vitamin E were found in red cabbage, garnet amaranth, and green daikon radish microgreens, respectively. In terms of carotenoids, cilantro microgreens showed the highest concentration of lutein/zeaxanthin and violaxanthin and ranked second in β-carotene concentration. In contrast, popcorn shoots and golden pea tendrils were relatively low in vitamins and carotenoids, although they were still comparable nutrition- ally to some commonly consumed mature vegetables. It is also noted that golden pea tendrils, which are grown in the absence of light, processed much lower vitamin and carotenoid concentrations than pea tendrils grown under light, suggesting that light plays an important role on nutriential values during the growth of microgreens. The data generated by this research likely provide a scientific basis for evaluating the vitamin and carotenoid concentrations of microgreen cotyledon leaves. It can also be used as a possible reference in estimating the dietary intake and adequacies of vitamins from microgreens. However, since growing, harvesting, and postharvest handling conditions may have a considerable impact on the synthesis and degradation of phytonutrients, including vitamins and carotenoids, additional studies may be needed to evaluate the effect of these agricultural practices on phytonutrient retention.