Ultrasound-assisted alkaline pH-shift process effects on structural and interfacial properties of proteins isolated from shrimp by-products

This study investigated the effects of alkaline pH-shift processing (pH: 12, 12.5 and 13) combined with ultrasonication (300 W; 0, 10, 20, and 30 min) on the yield and functional characteristics of shrimp proteins. Ultrasound assistant pH-shift processing resulted in a significantly higher protein recovery than the alkaline pH-shifting as maximum protein recovery was obtained at pH 12.5 in combination with sonication for 30 min (25.12%). Applying ultrasonication during the alkaline solubilization remarkably (P < 0.05) decreased zeta potential and particle size of the recovered shrimp proteins while increasing their surface hydrophobicity, fluorescence intensity, and reactive sulfhydryl content. The combination led to the denaturation of the recovered proteins with a change in their alpha-helices, beta-sheet, random coil and beta-turn content. Foaming and emulsifying characteristics of the shrimp proteins were remarkably (P < 0.05) affected by using the combined treatment, however, the progress level was dependent on the ultrasonication time and the solubilization pH. The highest value in emulsifying activity and foaming capacity was obtained in the sample extracted at pH 12.5 in combination with ultrasound for 20 min (300 W). Altogether, applying ultrasonication during the pH-shift processing can help protein isolation from shrimp peeling by-products but the combination should be carefully tuned to achieve maximum protein functionality.