Deccan hemp (Hibiscus cannabinus) seed as a sustainable protein source: Impact of ultrasound coupled alkaline extraction on structural, functional, nutritional, and rheological properties

• Deccan hemp ( Hibiscus canna binus) seed can be a promising source of plant protein. • Ultrasound-coupled extraction improved protein yield and functionality. • Ultrasound modified the protein's structure, improved surface charge and solubility.. • Enhanced emulsifying nature of ultrasound treated protein. • Ultrasound improved the in vitro digestibility and nutritional quality of protein. This study evaluates the effect of ultrasound-assisted alkaline extraction on the properties of Deccan hemp seed protein (DHSP) isolate. The functional attributes, structural characteristics, nutritional quality, and rheological properties of DHSP obtained through alkaline extraction alone were compared with those obtained from ultrasound-coupled alkaline extraction. The findings revealed that protein yield and purity increased with higher ultrasound amplitude and extended treatment time. Ultrasound treatment also enhanced the solubility, least gelation concentration, water absorption, and oil holding capacities of DHSP. Modifications in the secondary structure of the ultrasound-extracted protein improved its emulsifying and foaming properties. Confocal laser scanning microscopy images confirmed the homogeneity and uniform distribution of oil droplets in emulsions based on ultrasound-treated protein. The improved structure-forming ability of ultrasound-coupled alkaline extracted DHSP is evidenced by intrinsic fluorescence, CD spectroscopy, free sulfhydryl group content, surface hydrophobicity, and zeta potential measurements. The maximum denaturation temperature and enthalpy observed are 112.25 °C and 96.55 J/g, respectively, at 75 % amplitude and 30 min of treatment. The essential amino acid content and in vitro digestibility of the ultrasound-treated DHSP are higher compared to those of the protein extracted solely by alkaline method. Thus, the ultrasound-coupled alkaline extraction process produced a DHSP isolate with superior functional properties and nutritional value, making it suitable for a variety of food applications.