Conjugation of sunflower meal protein hydrolysates with chlorogenic acid: Structural changes and functional properties

Appropriate modification of sunflower meal protein with polyphenols can greatly increase its functional properties and improve the utilization rate of by-product as a lower price protein source. The present work analyzed effects of covalent conjugation of chlorogenic acid (CGA) to sunflower meal protein hydrolysate (SMPH) on its structural and functional properties. Covalent modification at increasing CGA concentrations (0.2–1.0 mg/mL) caused color changes, reduced free amino, thiol, and tyrosine groups, as well as significantly increased particle size and polyphenol bound equivalents of SMPH. Enhanced random coil content indicated protein unfolding and structural disorder. Fluorescence intensity and surface hydrophobicity decreased, indicating that CGA and SMPH had interacted. Antioxidant activity and emulsifying capacity improved dose-dependently, with 1.0 mg/mL CGA yielding the highest ABTS· + and DPPH· radical scavenging, and an emulsifying activity index. This study has practical application for the high-value utilization of sunflower meal protein in functional foods. • Chlorogenic acid was covalently conjugated to sunflower meal protein hydrolysate. • Increasing chlorogenic acid amount reduced the free amino, thiol, and tyrosine groups. • Conjugation increased the random coil content and formation of disordered structures. • Covalent conjugation enhanced the emulsifying capability and antioxidant capacity. • Conjugates from by-product have potential applications as functional food ingredients.