Structure characteristics and functionality of water-soluble fraction from high-intensity ultrasound treated pea protein isolate

Abstract

High-intensity ultrasound (HIUS) has been widely utilized as an emerging technique to modify the functionality of proteins. However, those findings exclusively pertained to the whole protein after the treatment of HIUS. Such protein consists of not only water-soluble proteins but other insoluble constituents, which cannot reflect the role of HIUS on the protein functionality. The objective of this study is to understand the influences of ultrasonic treatment (20 kHz) at varying power (200, 300 or 500 W) and time (5, 10 or 20 min) exclusively on structural and functional properties of water-soluble fraction (WPPI) harvested from HIUS treated pea protein isolate (PPI). Relevant parameters of ultrasound including ultrasonic intensity and ultrasonic density were determined. No significant changes on the primary structure of WPPI were observed from electrophoresis and size exclusion chromatography analysis. Fourier-transform infrared spectroscopy analysis as well as intrinsic and extrinsic fluorescence spectroscopy showed that HIUS was able to change the secondary and tertiary structure of WPPI. HIUS treatment drastically improved protein content and absolute solubility of pea protein. The underlying mechanism lies in the roles of HIUS to change the secondary and tertiary structure and to increase the magnitude of surface charge of WPPI, as well as to facilitate the coexistence of both smaller particle size pea protein and soluble aggregates. HIUS exerted an adverse effect on emulsification properties but improved foaming stability. The results of this study provide a theoretical basis to unravel the essential role of HIUS on modifying the structure of plant protein and the corresponding functionality.