Green solvents could unlock plant protein from rapeseed waste

Heriot-Watt University researchers have developed a new method to extract high-quality protein from rapeseed waste using environmentally friendly solvents, potentially offering a sustainable solution to the world's growing protein demands.

The research is reported in the journal Food Hydrocolloids.

Global protein demand is expected to double by 2050; the plant protein market alone is projected to grow from £13.7 billion to £21.3 billion between 2027 and 2030.

Professor Stephen Euston, from Heriot-Watt University's School of Engineering and Physical Sciences, said: “Livestock farming produces high levels of greenhouse gases, creating a serious environmental challenge as demand for animal protein grows.

“We need alternative sources of protein that don’t cost the earth.”

Euston and his colleagues have focused on rapeseed press cake, the protein-rich waste left after oil extraction.

“Rapeseed press cake has been an underused resource, and upgrading it for human consumption would make a lot of sense - there’s a lot available in Scotland, as farmers use rapeseed as a break crop, and the market for the oil has been growing.”

“It contains 28-45% protein, depending on the processing method, and most of this nutritious material goes unused for human consumption.”

Natural solution

Euston worked with student Grace Chidimma James to investigate whether natural deep eutectic solvents (NADES) could effectively extract protein from rapeseed press cake.

Grace said: “NADES are eco-friendly alternatives to the harsh chemical solvents traditionally used in protein extraction.

“They have low toxicity and are biodegradable. They are also low-cost.”

The solvents are created by combining natural compounds such as betaine, a naturally occurring compound found in beetroot and other sources, with citric acid, or choline chloride, a type of salt, with glycerol, forming liquids that can extract proteins without environmental damage.

Double the protein extracted

The study found that certain NADES formulations could extract significantly more protein than conventional water-based methods.

Using advanced computer simulations, the researchers discovered how these green solvents work at the molecular level. The NADES components form hydrogen bonds with proteins, potentially weakening their attachment to other materials in the rapeseed cake and making extraction easier.

The most effective combination - betaine and citric acid in a 2:1 ratio - achieved protein yields of 53%, compared to just 15% with water extraction alone.

Euston said: "While extraction with water alone gave the highest protein purity, NADES formulations were able to increase the protein yield significantly.

“However, the higher yields came at the cost of purity. The extracted protein contained other plant compounds alongside the proteins we hoped for - so there’s some work to be done on refining the process.”

Towards commercialisation

While promising, the technology still faces hurdles before it can be commercialised.

Euston said: "More research is required on optimising both the choice of components and concentration of species to maximise yield and purity of protein extracts.

“But this is a step towards a more sustainable food system, where agricultural waste could be upgraded for human consumption.”