Hot air drying effectively preserves nutrients and health compounds in microgreens

Hot air drying — a cheap and relatively easy preservation technique — improves the availability of key nutrients and plant compounds in microgreens that benefit health, according to new food research. When kept fresh, these highly nutritious young seedlings of cruciferous vegetables like radish, broccoli, and kale are highly perishable and lose nutritional value quickly.

Microgreens contain nutrients such as vitamins, minerals, and bioactive antioxidants, like polyphenols and glucosinolates.

“Microgreens increasingly are popular due to their high concentrations of health-promoting compounds, but their benefits have been limited because they’re highly perishable, lasting only one to two days at room temperature and seven to 14 days with refrigeration,” says senior author and team leader Joshua Lambert, professor of food science in the College of Agricultural Sciences at the Pennsylvania State University (Penn State), US.

“That limits their use, increases costs, and leads to food waste — especially in places without good refrigeration. So, there’s a clear need for preservation methods that keep nutrients intact.”

Clean label preservation

The researchers found that radish microgreens, no matter at what temperature they were dried, retained a significant portion of nutrients.

“Hot air drying, even at higher temperatures, can be an effective way to preserve nutrients in radish microgreens, especially for making powders that can be used in food products,” says Marjorie Jauregui, a pilot plant research technologist at Penn State.

“While some nutrients are lost, others remain stable and, overall, hot air drying is a practical and promising postharvest method.”

From their drying experiments, the team specifically found that radish microgreens retained 91% of their total phenolic content — antioxidants — after drying at 113 °F and 79% after drying at 149 °F.

Those dried at 203 °F retained 100% of glucoraphenin — a specific glucosinolate with potential anti-cancer properties. This compound was stable after drying at 113 °F and 149 °F and retained 78% after drying at 203 °F.

Vitamins B1 and B9 were stable at all drying temperatures. The microgreens retained  vitamins B2, B3, and C by up to 65%, 64%, and 37%, respectively, after heat exposure.

Simulated digestion reveals bioaccessibility rates

The researchers measured the effects of drying methods on nutrient bioaccessibility. They did this by simulating digestion in a laboratory process that recreates the digestive environment of the human gastrointestinal tract.

The findings may help make nutrient-dense microgreen powders more accessible and sustainable, especially for areas lacking refrigeration or advanced drying technology.

The team found that total phenolic content and vitamins B1, B3, B9, and C were bioaccessible, ranging from 13% to 68%, with no major differences across the drying methods.

Lambert claims vitamin B2 was more bioaccessible after being dried at 149 °F than at other temperatures.

The researchers did not detect glucoraphenin and anthocyanins after the simulated digestion, meaning these compounds broke down or became unmeasurable. These polyphenols can also act as antioxidants, offering potential health benefits such as supporting cardiovascular and immune health.

Metabolomic analysis further revealed that different drying methods led to different overall chemical profiles, notes Jauregui.

Glucosinolates and flavonoids — plant pigments that provide different health benefits — were major contributors to these differences, she explains. Because microgreens are increasingly promoted for healthy eating, understanding how to preserve their nutrients without expensive equipment is essential.

The researchers say their results may help make nutrient-dense microgreen powders more accessible and sustainable, especially for areas lacking refrigeration or advanced drying technology.

“Hot air drying is more practical,” says Lambert, “especially in low-resource areas, but we need to fully understand how different drying temperatures affect key nutrients and phytochemicals — plant compounds that provide health benefits. These results are more than a good start.”

The findings are published in the Journal of Food Science.