Ecological extraction of protein from broccoli (Brassica oleracea var. italica) stem residues

The search for innovative and ecological techniques to obtain high-value compounds from waste materials with a lower impact on the environment is prevailing. Particularly, in protein extraction, utilizing plant waste can reduce environmental impact by taking advantage of residues that, if not properly managed, contribute to soil and air pollution. Deep eutectic solvents (DES) emerge as a sustainable and efficient alternative to plant protein extraction, aiming to replace organic solvents, which are generally toxic. Similarly, employing eco-friendly techniques for the extraction of protein is crucial, with ultrasonication being widely recognized as a green technology. By combining these strategies, an important decrease in environmental impact can be feasible. In the present work, we compared ultrasound-assisted protein extraction (80% amplitude, 30 ºC, 15 min) from a dried broccoli stem sample using two different solvents: ethanol and a deep eutectic solvent consisting of sodium acetate and urea (NaOAc:urea). Total protein was determined by the Bradford technique, showing that using ethanol for the extraction makes it possible to obtain an average of 0.212 ± 0.07 mg/mL, while with the DES the total protein obtained was 0.778 ± 0.09 mg/mL. We optimized ultrasound-assisted protein extraction using NaOAc:urea, assessing time, temperature, and amplitude. Ultrasonic amplitude and extraction time were the most critical factors. The optimal condition was 15 min of sonication at 80% amplitude and 40 ºC, which maximized the protein yield. This demonstrates that broccoli stems, as plant waste, represent a valuable source of protein. Also, that using DES for protein extraction from broccoli stems could maximize its utilization and contribute to a more sustainable cycle in plant protein production, as it may reduce the environmental impact associated with traditional solvents, and is also more effective in protein extraction.