In this study, ultrasound pretreatments of sunflower-meal protein (SMP) to yield high antioxidant
capacity from its hydrolysates by response surface methodology were optimized.
Optimization of experimental conditions was achieved to examine the impact of temperature,
solvent-solid ratio and sonication time on antioxidant capacities of SMP hydrolysates
with Box–Behnken's design. Quadratic models of DPPH-scavenging activity (DPPHSA),
hydroxyl-radical scavenging activity (HRSA), and Cu2+ and Fe2+ chelating activity (Cu2+-CA
and Fe2+-CA) were developed, and their coefficients observed from multiple-regression
analysis. ANOVA indicated that time was highly significant (p < .01) on all experimental
responses. The best experimental point of DPPHSA, HRSA, Cu2+-CA, and Fe2+-CA was
accessed at 42.50
C, 18.16 mL/g and 26.52 min and the predicted data for these
responses were 52.09, 70.05, 50.85, and 43.35%, respectively. Outcome of verification
experiment was reliable with predicted data for all responses. Additionally, DPPHSA,
HRSA, Cu2+-CA, and Fe2+-CA of pretreated hydrolysate improved (p < .05) by 17.41,
20.00, 14.72, and 26.41%, respectively over nonsonicated hydrolysate. Amino acid content
and hydrophobicity of SMP hydrolysate at the optimum sonication condition were
analyzed. Analyses indicated that ultrasonication could facilitate the releasing/unfolding of
hydrophobic amino acids from SMP over nonsonicated samples during enzymolysis with
high antioxidative capacity.