Researchers at the University of Missouri report that pairing kale with oil-based dressings or specially designed nanoemulsion sauces significantly improves the bioaccessibility of its key carotenoid nutrients in a lab model of human digestion. Cooking kale alone does not enhance this process, but oil-containing dressings and advanced emulsified sauces appear to offer greater benefits, potentially informing new food products aimed at maximizing vegetable nutrition.
Kale is widely recognized for its carotenoid content, including lutein, α-carotene and β-carotene, compounds associated in prior research with benefits such as stronger immunity, improved vision and a reduced risk of chronic diseases like diabetes, heart disease and some cancers. These carotenoids, along with vitamins C and E and other bioactive plant chemicals in kale, are fat‑soluble, which makes them harder for the body to absorb without an accompanying fat source, according to researchers at the University of Missouri-Columbia.
"Kale is a nutrient-rich vegetable that contains carotenoids, including lutein, α-carotene and β-carotene, which have beneficial effects on overall health," said Ruojie (Vanessa) Zhang, an assistant professor in the Division of Food, Nutrition and Exercise Sciences at the University of Missouri's College of Agriculture, Food and Natural Resources (CAFNR). "The problem is our bodies have a hard time absorbing these nutrients because they are fat-soluble rather than water-soluble," she explained, in remarks released by the university.
To explore how preparation methods influence carotenoid uptake, Zhang and her colleagues used a laboratory model that mimics human digestion. As described by the University of Missouri and in coverage by outlets including ScienceDaily and MedicalXpress, the team tested kale prepared in several ways: eaten raw, cooked, eaten raw or cooked with oil-based dressings or sauces such as olive oil or mayonnaise, and cooked directly in sauce.
In this in vitro system, raw kale on its own led to very low carotenoid bioaccessibility, and cooking kale without added fat slightly reduced that bioaccessibility further. When the researchers added conventional oil-based dressings or sauces, carotenoid uptake increased markedly, whether the kale was raw or cooked, according to the university summary.
The largest gains came from a specially formulated nanoemulsion-based sauce, an excipient emulsion designed to enhance the release of fat-soluble compounds during digestion. In the simulated digestion model, this nanoemulsion sauce dramatically increased the proportion of lutein, α-carotene and β-carotene that became bioaccessible from both raw and cooked kale. Cooking the kale directly in the nanoemulsion-based sauce produced similar improvements to adding the sauce after cooking, ScienceDaily and related reports note.
The findings are detailed in a peer-reviewed paper titled "Culinary strategies for improving carotenoid bioaccessibility in kale: The role of thermal processing and excipient emulsions," published in 2025 in the journal Food Nutrition (volume 1, issue 2, article 100049). The study was authored by Hangxin Zhu, David Julian McClements, Zipei Zhang and Ruojie Zhang.
Co-authors include Dr. Zipei Zhang from the University of Missouri's College of Agriculture, Food and Natural Resources; doctoral student Hangxin Zhu from the same institution; and Dr. David Julian McClements from the University of Massachusetts Amherst, according to the University of Missouri and ScienceDaily.
Zhang said the work points to practical strategies for helping people obtain more nutritional value from vegetables simply by changing how foods are prepared or seasoned. "Our team is committed to advancing food science with the goal of improving human health through the development of innovative foods and technologies," she said in statements released by the university and cited by several outlets. The research team is also exploring how nanotechnology-inspired dressings might be further optimized, with the aim of enhancing nutrient absorption not only from kale but potentially from other vegetables as well.
While the current results come from in vitro digestion models rather than human feeding trials, they offer a science-based rationale for pairing kale and other carotenoid-rich vegetables with appropriate sources of dietary fat, such as oil-based dressings, to improve carotenoid bioaccessibility.
