Title : Ultrasound Assisted protein extraction from distiller’s rice spent grain: Advancing agro- industrial by-product valorisation for food applications
Abstract:
Distiller’s rice spent grain is the predominant solid residue of the rice-based ethanol industry, accounting for approximately 85% of total byproducts generated. On average, 20 kg of spent grain is generated from 100 L of ethanol produced. According to the Renewable Fuels Association (2025), global ethanol production reached 31.3 billion gallons (approximately 118.5 billion liters), corresponding to an estimated co-production of 23.7 million tons of spent grain. Nearly 20% of the generated spent grain is landfilled, each ton emitting 514 kg CO2 per ton, thereby exacerbating the environmental burden. The large volume of underutilized spent grain reinforces the need to move from disposal-based management to value-driven utilization. With a crude protein content of 50 %, distiller's rice spent grain constitutes a viable substrate for protein extraction and valorization. Therefore, this research optimized the ultrasound-assisted alkaline ethanol extraction of protein from distiller's rice spent grain to obtain a protein concentrate. The effects of ultrasonication power (300-450W), extraction duration (10-2min), and duty cycle (60-90 %) were systematically evaluated. An alkaline-ethanol solvent (45% ethanol: 55% 0.1 N NaOH) was used for extraction along with ultrasonication, followed by isoelectric precipitation at pH 4.8 using 1 M HCl. Optimal conditions (350W, 15min, 90% duty cycle) achieved maximum protein yield (26.40%) and purity (82%). The recovered protein exhibited functional properties, namely, emulsification and water/oil absorption capacities, comparable to commercial protein isolate. These results indicate that distiller’s rice spent grain protein concentrate can serve as an ingredient in various food products, highlighting the potential of industrial by-product valorization to support sustainable circular bioeconomy frameworks.
