Upscaling the rice processing by-products for protein using conventional and novel methods

Rice processing generates substantial by-products with untapped potential for value-added applications. These by-products, including rice bran, and broken rice, are rich in nutrients that can be transformed into functional ingredients for various industries. Optimizing the extraction processes to obtain high-yield and high-quality rice bran protein is essential to understanding its functionality and end applicability. This study explored the possibilities of upscaling rice processing by-products to turn them into functional food processing and development ingredients.

The rice milling byproducts bran, brown rice, and broken rice were subjected to protein fractionation to understand the subunit composition and their characteristics. Further, as bran is the major milling byproduct, extraction of rice bran protein has certain drawbacks, such as low yield and quality. The defatted rice bran was extracted with alkaline extraction at pH 9.0 and alkaline-acid extraction at pH 9.0 and 2.0. Post-extraction, the precipitation will be done at an isoelectric point of pH 4.5 using heat coagulation at 70°C. Consequently, ultrasound was used as an intensification pretreatment to improve protein recovery and functionality. The processes were evaluated by testing proteins' functional properties and secondary and tertiary structure.

The broken rice had the highest concentration of glutelin, ~67%, while rice bran predominantly comprised of albumin, ~36%. Furthermore, protein recovery was higher with both acid and heat than alkaline extractions, and heat coagulation improved by 2-fold. Ultrasound-assisted extraction and conventional isoelectric precipitation (UAE-IP) methods exhibited the highest protein yield of 65.7%, while conventional extraction yielded 38.9%. Ultrasound treatment induced substantial structural modifications, including a 96.8% increase in β-sheets with UAE-UIP. Ultrasound extraction and precipitation generally enhanced protein digestibility, with AE-UIP showing the highest digestion rates, although excessive ultrasound could reduce digestibility. The developed extraction techniques improved the extractability, functionality and structural properties of the proteins, improving their product applicability and end usage.