Turning kale waste into treasure

Scientists from NTU Singapore have developed a new technique to convert kale waste for use in health and personal care products, reducing food waste and emissions.

Phytochemicals found in plants are known to prevent damage to cells in the body and are widely used in consumer products. They include health-promoting supplements, like antioxidants and lutein, as well as face scrubs and hair shampoo with kale extracts.

Current processes for extracting phytochemicals from kale are energy-intensive, requiring high pressure and temperatures, which contribute additional CO₂ emissions to the environment.

The NTU researchers sought a more valuable, sustainable and efficient solution by mixing processed kale waste with naturally derived natural deep eutectic solvents (NADES) - non-toxic liquids made up of plant-based compounds such as amino acid, sugar, and vegetable oil by-product – and found that when the kale waste and NADES mixture is stirred and set aside, it naturally separated into layers, facilitating the easy extraction of the phytochemicals from kale (polyphenols, carotenoids, and chlorophylls) without the need for heating.

The lead author of the study, Professor Hu Xiao from the NTU School of Materials Science and Engineering (MSE) and Programme Director, Sustainable Chemistry & Materials, Nanyang Environment & Water Research Institute (NEWRI), said: “The use of non-toxic and naturally derived solvents in our method makes it a food-safe technique. At the same time, our method preserves the potency of the extracted active ingredients, making it highly attractive for industry adoption.

“The extracted nutrients can potentially be used for applications in personal care products, cosmetics, food supplements, and herbal extracts.”

Looking to the future, the scientists are investigating the feasibility of applying their newly developed method to extract beneficial compounds from other types of fruits and vegetables, and medicinal plants such as dragon fruit, spinach, and lettuce.