Effect of ultrasound-assisted pH shift treatment on structure and functional properties of mulberry leaf protein

Abstract

This study investigated the impact of multifrequency ultrasound (22/28/40 kHz)-assisted pH shift treatment on the structural and functional attributes of mulberry leaf protein (MLP). The results showed that ultrasound-assisted pH shift increased the solubility of MLP by 281.74 % and significantly increased its emulsifying activity index (from 188.63 ± 3.27–231.41 ± 5.22 m²/g), emulsion stability index (from 51.22 ± 2.67–136.20 ± 9.98) and in vitro protein digestibility (from 41.75 % ± 3.57–72.54 % ± 1.38 %). The reduction in MLP particle size and the increase in zeta potential indicated that the treatment disrupted the tertiary structure. Furthermore, the increases in ultraviolet absorbance, fluorescence intensity, and molecular flexibility revealed significant alterations in the secondary and tertiary structures induced by ultrasound-assisted pH shift. The treatment reduced the α-helix content, while increased the β-sheet content, suggesting partial unfolding in the secondary structure of MLP, which led to the increase of exposed hydrophobic groups. As a result, the surface hydrophobicity of MLP was increased after ultrasound-assisted pH shift treatment. In conclusion, ultrasound-assisted pH shift treatment holds promise for advancing the application of MLP in the food industry.