The impact of ultrasound duration on the structure of β-lactoglobulin

This study aimed to investigate how ultrasound treatment for different durations (0, 10, 20, 30, 60, and 90 min) impacts the hydrolysis and structural characteristics of p-lactoglobulin (beta-LG). Ultrasound conditions were set at ultrasound frequency (40 +/- 2) kHz, power 600 W, power density 111.1 W/L, pulse on/off time 10 s/3 s, scanning period 500 ms, and temperature 25 degrees C. beta-LG was pretreated with ultrasound and hydrolyzed by alcalase. Ultrasound treatment for 20 and 30 min significantly improved the degree of hydrolysis and peptide yield; longer treatment durations (60 and 90 min) had little effect on these parameters. Ultrasound treatment caused dynamic changes in protein structure. After a 30-min ultrasound treatment, the particle size, free sulfhydryl groups, intrinsic fluorescence, surface roughness, alpha-helix, and beta-turns increased, whereas absolute zeta potential, disulfide bonds, and beta-sheets decreased. When the duration of treatment increased from 30 min to 90 min, the opposite trend was observed. Short-duration ultrasound treatment induced partial unfolding of beta-LG, while long-duration treatment induced protein aggregation. Therefore, physicochemical and structural changes in beta-LG are largely dependent on ultrasound treatment duration.