Waste Not
Researchers Upcycling Kale, Plastic Waste Into Personal Care, Pharmaceutical Ingredients

NTU Singapore scientists develop sustainable way to convert kale waste into products for health, personal care

Reshma Beauty is one of many personal-care brands that uses kale in its products | Image credit: Reshma Beauty

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

Millions of tonnes of food and vegetables are discarded globally every year. In the case of leafy vegetables such as kale and lettuce, farmers cut off outer leaves as they are harvested in order to sell perfectly sized and aesthetically pleasing vegetables with no signs of damage or yellowing. This commercial practice results in a significant amount of perfectly good, edible leaves being thrown away. In Singapore alone, some 817,000 tonnes of food waste were generated in 2021 — almost half of which was fruit and vegetables.

Phytochemicals found in plants are known to prevent damage to cells in the body and are widely used in health and personal-care products — including nutritional supplements such as antioxidants and lutein; as well as face scrubs and 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. Moreover, industrial extraction processes only target a single type of phytochemical each time.

Seeking a more sustainable and efficient method to turn vegetable waste into “treasure,” the NTU researchers looked to 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 — for answers. While NADES have long been studied in separation technology for food and pharmaceutical industries, not much is known about their ability to extract different classes of bioactive compounds from vegetable waste.

Focusing on bioactive compounds in kale, the NTU research team explored a range of NADES — mixing them with processed kale waste to observe how molecules reacted to each other.

After repeated testing, the researchers established the best NADES solvent for optimal extraction of bioactive compounds. The NTU team 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.

Since there is no need to heat or pre-treat the kale waste — for example, by freeze drying — the costs, as well as the emissions, of the simpler extraction process are kept down. The NTU research team is confident their new method would be scalable and attractive, cost-wise, to the industry.

“The use of non-toxic and naturally derived solvents in our method makes it a food-safe technique,” said Hu Xiao, Professor at the NTU School of Materials Science and Engineering, Program Director of Sustainable Chemistry & Materials at Nanyang Environment & Water Research Institute, and lead author of the study. “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.”

The NTU research team said that their waste-to-resource approach tackles both food waste and carbon emissions, supporting the development of a zero-waste, circular economy.

The study, published in the scientific journal Separation and Purification Technology in July, is aligned with the research pillar of NTU 2025 — the University’s five-year strategic plan which aims to leverage innovative research to mitigate human impact on the environment.

Investigating approaches for use with other crop waste

The NTU team has filed a patent in Singapore for its non-toxic, high-yield extraction technique (learn more about it here). For their next steps, the researchers are investigating the feasibility of applying their newly developed method to extract beneficial compounds from other types of fruits, vegetables and medicinal plants such as dragon fruit, spinach and lettuce.

Kale waste for the study was provided by Sustenir Agriculture, a Singapore-based, high-tech urban-farming company. The kale leaves used for the research did not meet commercial quality standards and were intended to be discarded as waste.

---

Scottish researchers turning plastic waste into neurological medications

API Foilmakers produces labels for a wide range of consumer products, including Johnnie Walker Scotch Whisky | Image credit: API Foilmakers

Meanwhile, a team of Scottish researchers is exploring what is believed to be a world first: a new process that could see plastic waste from industrial processes become pharmaceuticals for neurological conditions.

Scientists from Impact Solutions, biotechnology researchers from the University of Edinburgh, packaging manufacturer API Foilmakers, and the Industrial Biotechnology Innovation Centre (IBioIC) are exploring the feasibility of a new approach to recycling polyethylene terephthalate (PET) — a type of plastic commonly used in the production of food and drink packaging.

The project represents the first time scientists have explored the use of PET as a starting point for manufacturing medication. Using genetically modified bacteria and enzymes to break down the plastic waste, the core chemical components can then be converted into valuable pharmaceuticals for treating a range of life-limiting conditions such as brain disorders.

API Foilmakers, which is providing the input material, specializes in rolls of plastic-backed foil for a variety of commercial packaging applications; it produces enough to stretch approximately 18 kilometers each month, creating up to 100 tonnes of PET waste. The printing method also means that one small error can render an entire roll unusable.

While other companies have been known to use enzymes to breakdown PET, this can often produce lower-quality plastic — which still languish in landfill in the long term.

As most pharmaceuticals are still petrochemical-based, and with medicines mostly manufactured overseas, the project represents an opportunity to develop more sustainable techniques.

“We are thrilled to be leading on this exciting project, which could have a major influence in the way we produce pharmaceuticals here in the UK,” said Simon Rathbone, Development manager at Impact Solutions. “By exploring the use of PET as part of the manufacturing method, we are not only addressing the environmental challenges posed by plastic waste but also creating a sustainable approach for producing essential medicines. At the moment, we are working towards a small-scale proof of concept — laying the foundation for the future commercialization of this technology. Of course, discussions around regulation and trials will come further down the line as we prove the capabilities of this process at scale.”

The researchers are also exploring the various paths from PET to other forms of medication, supporting the UK government’s Life Sciences Vision to create a globally competitive environment for life-sciences manufacturing in the UK — building resilience in response to international disruption and shortages experienced during the pandemic.

“There’s potential for this to be a turning point for the pharmaceutical sector,” said Dr Stephen Wallace, UKRI Future Leaders Fellow and senior lecturer in biotechnology at University of Edinburgh. “While this project is focused on a specific type of plastic waste from the foil rolls, it’s a platform technology that could in the future be applied to alternative forms of waste PET from other sectors — if we get the foundations right. We’ve already had some promising talks with big pharma companies keen to explore this new approach.”