Effect of ultrasonic-assisted enzymatic extraction on proso millet bran protein: extraction rate, structural and functional properties.

Abstract

Background: Proso millet bran protein (PMBP), derived from agricultural by-products, possesses high nutritional value, despite its challenging extraction process. The present study proposes an extraction method for PMBP using ultrasound-assisted cellulase technology (UAE), and optimizes the process parameters. Non-waxy (N-PMBP) and waxy (W-PMBP) PMBPs, extracted through alkaline solubilization and acid precipitation (conventional treatment, CT), served as control groups to assess the impact of UAE on the structure and functionality of PMBP, as well as the distinctions between N-PMBPs and W-PMBPs.

Results: At an ultrasonic power of 420 W, cellulase concentration of 80 U g^-1, enzymolysis pH of 5.0, enzymolysis temperature of 55 °C and enzymolysis time of 3 h, the maximum PMBP extraction rate was achieved at 76.80%. Compared to CT, UAE extraction resulted in enhancements in α-helix and random content, particle size, surface hydrophobicity (H₀) and ξ-potential value, leading to improved functionality of the PMBPs. Additionally, significant functional and structural disparities were observed between N-PMBPs and W-PMBPs. Although no significant difference in molecular weight was detected, each exhibited three major bands. W-PMBPs exhibited significantly higher beta-sheet content compared to N-PMBPs, whereas the reverse trend was observed for α-helix content. W-PMBPs displayed strong solubility and water/oil holding capacity compared to N-PMBPs, albeit with lower emulsifying properties and H₀.

Conclusion: UAE could enhance PMBP extraction, inducing structural and functional changes in PMBPs compared to CT. Significant differences in functionality and structure were observed between N-PMBPs and W-PMBPs, providing fundamental data and a theoretical basis for PMBP development and utilization. © 2025 Society of Chemical Industry.