Impact of High-Intensity Ultrasound on Cowpea Protein Extractability, Structural, and Techno-functional Properties

Abstract

The growing demand for plant-based proteins has prompted the exploration of alternative sources such as cowpea (Vigna unguiculata), due to its high protein content (26–28%). This study compared two protein extraction methods: 1)the pH-shift method at pH 7.5, 8.0, and 9.0, and at the natural pH of the cowpea flour–water dispersion (pH 6.4); 2)pH-shift protein extraction assisted by high-intensity ultrasound (HIUS; 400 W, 60 min, pulse 2 s on/2 s off, 30 ± 1 °C). Protein isolates obtained at pH 7.5, 8.0, 9.0, and 6.4 are hereafter referred to as I7.5, I8, I9, and I6.4, respectively, while ultrasound-assisted samples are designated with the suffix “-US.” Protein yield, structural modifications, thermal stability, and techno-functional properties were assessed. Protein content ranged from 77.85% to 83.0%. HIUS increased yield at all pH conditions, including at pH 6.4. HIUS induced partial unfolding, increased surface hydrophobicity, and decreased thermal stability as a function of pH-shift extraction. These structural changes improved solubility at pH 6.0 and enhanced emulsifying capacity, especially in I7.5-US and I8-US, forming emulsions with smaller droplet sizes. I6.4-US was particularly attractive, providing yields and solubility comparable to or higher than I9 while avoiding the use of highly alkaline solutions. Although HIUS-assisted extraction slightly reduced protein purity due to co-extraction of non-protein compounds, it represents a simpler and more sustainable approach. This strategy supports the development of plant-based protein ingredients with high functionality and reduced chemical usage.