Microgreens: Assessment of Nutrient Concentrations

Abstract: Microgreens (seedlings of edible vegetables and herbs) have gained popularity as a new culinary trend over the past few years. Although small in size, microgreens can provide surprisingly intense flavors, vivid colors, and crisp textures and can be served as an edible garnish or a new salad ingredient. However, no scientific data are currently available on the nutritional content of microgreens. 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 γtocopherol 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.

Introduction: 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 The new Dietary Guidelines for Americans (2010) released by the U.S. Department of Agriculture (USDA) and the Department of Health and Human Services (DHHS) specifically recommends Americans to fill half of their plate with fruits and vegetables because they possess benefits for human health. Microgreens are an exotic genre of edible greens, appearing in upscale markets and restaurants, that have gained popularity as a new culinary trend over the past few years. 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. Therefore, microgreens can be served as a new ingredient in salad, soups, and sandwiches, enhancing their color, texture, and/or flavor, and also can be used as edible garnish to brighten up a wide variety of main dishes.5−8 Although microgreens have been claimed as nutritionally beneficial, to the best of our knowledge, no scientific data are available on the exact phytochemical content of microgreens. Limited studies have shown that some young seedlings may have much higher levels of vitamins, minerals, and other healthgiving phytonutrients than the mature leaves. In a recent study from Lester et al.,9 it was reported that the younger leaves of baby spinach (Spinacia oleracea L.) generally had higher levels of phytonutrients: vitamins C, B9 and K1, and the carotenoids (lutein, violaxanthin, zeaxanthin and β-carotene) than the more mature leaves. Oh et al.10 also found that young lettuce (Lactuca sativa) seedlings, 7 days after germination, had the highest total phenolic concentration and antioxidant capacity in comparison to the older leaves. Therefore, the object of this study was to assess the vitamin and carotenoid concentrations of the 25 commercially available varieties of microgreens. The human bioactive compounds assayed include ascorbic acid (total, free, and dehydro), carotenoids (β-carotene, violaxanthin, and lutein/zeaxanthin), phylloquinone, and tocopherols (α- and γ-tocopherol).

Summary: In summary, the essential vitamin and carotenoid concentrations 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 nutritionally 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.

[For more journal articles & inspiration check out The Journal of Agricultural and Food Chemistry.]