Mustard bran’s second life: selective recovery of natural compounds

Keywords: By-product, Natural compound, Separation processes, Antioxidant, Circular economy

From mustard bran to hidden treasure

Sinapic acid (SA) is a phenolic compound known for its antioxidant, anti-inflammatory, and antibacterial properties. This make it a valuable compound for applications in medicine, food, and cosmetics. SA can also be used as a greener platform molecule in green chemistry. Today, it is mainly produced by chemical synthesis, with high purity (> 95 %) but at a very high price, about 1000 €/kg. Plants could offer a more sustainable route, particularly, Brassicaceae family, such as, mustard bran.

The processing of mustard seeds produces huge amounts of bran. Each year, global mustard seed production reaches over 800 kilotons. About 60 % of the seed weight converted into by-products, i.e. bran, usually underused or discarded. A high value-added use is to recover phytochemicals: phenolic compounds, particularly sinapic acid derivatives. Yet, current methods produce very low purity SA, typically below 3 %, making recovery from bran a big challenge!

Turning agricultural residues into high-value compounds

Scientists from SayFood and URD ABI are therefore exploring how to recover sinapic acid efficiently and sustainably from mustard bran hydrolysate. They first produce mustard bran hydrolysate, a liquid obtained by extracting the bran with water and enzymes.

Then, they explore three SA recovery approaches:

• 1st way: Adsorption on macroporous resins

Here, the compounds in the hydrolysate are adsorbed on the resin if they have a high affinity. They are later recovered by a suitable solution. By optimizing the process, scientists removed nearly all hydrophilic impurities. They increased sinapic acid concentration 8.6-fold, improved antioxidant activity 7.4-fold, and raised purity up to 18.4 %, with a high recovery yield (> 97 %).

• 2nd way: Membrane filtration pretreatment + Adsorption

As a practical clean-up before adsorption, the team used ultrafiltration or nanofiltration to retain major impurities. This step improved the resin’s adsorption capacity for sinapic acid. In the {nanofiltration + adsorption} combination route, sinapic acid purity jumped to about 55%, and antioxidant activity rose 12-fold.

• 3rd way: Solvent extraction in membrane contactor

Here, two liquids flow on each side of the membrane: the aqueous hydrolysate containing SA, and a hydrophobic organic solvent. Compounds are separated by their partitioning behavior: SA transfers to the organic phase, while hydrophilic impurities remain in aqueous phase. This route increased purity to 30 % and led to a 3-fold increase in antioxidant activity.

Guidance for eco-design…

To keep sustainability at the forefront, the team ran an early-stage life cycle assessment (a quick environmental “checkup” used to steer design before scale-up). The results indicate that the {nanofiltration + adsorption} route carries the highest environmental impact, followed by the other two options. Key hotspots are electricity, deionized water and chemicals use. With this information, researchers can target the biggest levers as processes move toward pilot scale.

This study shows that advanced purification routes can convert mustard bran hydrolysate into a valuable and bio-based compound. The combined process is promising for achieving high purity, while the initial environmental assessment helps balance performance with impact. Looking forward, efforts should focus on scaling up the most effective route and conducting a techno-economic analysis to evaluate industrial viability.