Cereal processing by-products and wastewater for sustainable protein extraction

The global food supply chain faces significant challenge due to substantial losses and waste, particularly in cereal processing. This review focuses on sustainable protein extraction from wastewater and by-products of key cereals, including rice, wheat, corn, millet, and oats. The structural conformation, molecular weight distribution, amino acid content, and bioactive characteristics of the extracted proteins were examined, highlighting their potential applications in food and allied industries. Certain proteins, such as globulins (52 kDa) and lipid transfer proteins (9 kDa), contribute to the functional qualities of rice by-products, which show strong antioxidant capacity. Zein and gliadins, two proteins found in maize and wheat, have noteworthy bioactive qualities but are linked to issues with allergenicity and high cost associated to their purification and extraction. The protein landscape is further diversified by oats and millet, which have distinct nutritional profiles and compositions. To enhance protein recovery while addressing cost and allergenicity constraints, biorefinery techniques integrating enzyme-assisted extraction with natural deep eutectic solvents (NADES) are explored. These methods not only improve extraction efficiency but also enhance protein bioavailability while reducing dependence on conventional solvents making the process more cost-effective and environmentally sustainable. The integration of these techniques within biorefinery frameworks enables simultaneous recovery of proteins, bioactive compounds, other high-value fractions, while significantly reducing food wastes and supporting circular economy principles. This review highlights the potential of cereal by-products as sustainable protein sources while emphasizing the crucial role of biorefineries in transforming these by-products into high-value products, contributing to a more sustainable and efficient food system.