Fine-Tuning Zinc Supplementation, Light Exposure To Boost Microgreens' Nutrition

Microgreens, which are young, edible plants that only take one to three weeks to harvest, are more than garnish at trendy restaurants — they could be the answer to global hunger, according to plant scientists at Penn State. Already densely packed with nutrients, microgreens can be made even more nutritious with a couple of minor growing adjustments. The research team that has experimented with different approaches for five years recently published the results of two new studies quantifying the nutritional results of supplementing microgreens with varied amounts of zinc during their growth, called agronomic biofortification, and exposing the plants to different amounts of light.

“Microgreens are ideal for zinc biofortification because they grow quickly, they’re very nutrient-dense and they contain low levels of antinutrients — compounds that can block zinc absorption,” said team leader Francesco Di Gioia, associate professor of vegetable crop science in the College of Agricultural Sciences, senior author on both new studies. “We provided zinc in fertigation — applying nutrients via irrigation — and analyzed the metabolomic profiles — comprehensive analyses of the molecules involved in the metabolism process in plant tissues — of pea and radish microgreens in response to light intensity and zinc fertilization inputs.”

First, in findings recently posted in Journal of Agricultural and Food Chemistry, the team reported how zinc enrichment and light intensity affect the nutritional composition of radish microgreens. They found that high light intensity increased antioxidants, such as vitamin C, flavonoids and phenolic acids in the tiny plants — compounds that play important roles in plant defense, growth and color, and also possess health benefits for humans.

Conversely, high light intensity decreased amino acids and glucosinolates, which are plant defense compounds. That suggests plants shift resources to fight light-related stress, according to Pradip Poudel, first author on both studies, who recently received a doctoral degree in agricultural and environmental plant science from Penn State. He is currently a postdoctoral scholar in Penn State’s Department of Food Science.

Zinc enrichment resulted in higher levels of specific antioxidants and more essential amino acids, the researchers found. It affected key plant metabolic pathways, changing phenylpropanoid metabolism, which is linked to antioxidants; nitrogen metabolism, which contributes to protein development; and energy metabolism, which increases adenosine triphosphate levels, signifying a boost in cellular energy and is often linked to photosynthesis and cellular respiration.

“The research shows how adjusting zinc levels and light exposure can help grow nutrient-rich, functional foods like radish microgreens that may support better health,” Di Gioia said. “It’s a step forward in fighting micronutrient deficiencies globally. Often called ‘hidden hunger,’ micronutrient malnutrition is a form of chronic undernutrition where people lack essential vitamins and minerals, despite consuming enough calories.”

Second, in findings available online ahead of publication in an October issue of Food Chemistry, the researchers reported on the results of growing pea microgreens with varying concentrations of zinc sulfate in irrigation solutions and exposure to various light intensity regimes.

They found that higher light intensity exposure led to the plants producing more flavonoids and phenolic acids, which are known for their antioxidant properties. This increase is likely a response to light stress, Poudel explained. Zinc enrichment increased levels of vitamin B1, B6 and C, and of sulfur-containing amino acids, all of which are nutrients critical for plant function and the health of plant consumers. Also, zinc enrichment raised oxalic acid levels, which may help the plant deal with excess metals in a process called detoxification, Poudel said.

From both studies, researchers concluded that light intensity affected the overall metabolite composition of the microgreens more than zinc levels did.

“This suggests that optimizing light is critical for improving the nutritional and functional quality of zinc-enriched microgreens,” Poudel said. “These studies help inform better growing strategies for producing microgreens aimed at reducing zinc deficiency. They’re excellent candidates for targeted zinc enrichment because they have a short growth cycle — harvested in seven to 21 days — they are low in phytic acid, which blocks zinc absorption and are popular as functional foods.”

Both of these studies were part of a larger research project that was Poudel’s doctoral thesis. For his efforts, he received both a Penn State Alumni Dissertation Award and the College of Agricultural Sciences Outstanding Dissertation Award.

Contributing to both studies were Kristen Jeffries, Jinhe Bai, Christina Dorado and Erin Rosskopf, U.S. Horticultural Research Laboratory, U.S. Department of Agriculture, Agricultural Research Services, Fort Pierce, Florida.

This research was funded by Open Philanthropy through the grant titled “Food Resilience in the Face of Catastrophic Global Events.” Additional support for these experiments was provided by the Pennsylvania Department of Agriculture and the U.S. Department of Agriculture’s National Institute of Food and Agriculture.

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