Interfacial behavior and antioxidant effect of esterified peptide FSEY (a hazelnut-derived tetrapeptide) in oil-in-water emulsions

The use of peptides as antioxidant additives in emulsified foods is limited due to their insolubility in the interfacial phase. Modification through alkylation provides a promising approach to overcome this issue. To evaluate the impact of esterification on the antioxidant ability of peptide in emulsion, a hazelnut-derived tetrapeptide Phe-Ser-Glu-Tyr (FSEY) was modified with alkyl chains of varying lengths. The antioxidant capacities and distribution patterns of FSEY and its esters were evaluated. As a result, modification through alkylation enhanced the antioxidant capacity of peptide FSEY, and a parabolic relationship was observed in the ability to inhibit oil oxidation. The ester modified with a butyl chain exhibited the highest inhibitory ability in emulsion stabilized by 0.5 g/100 g of Tween-20. Specifically, esters modified with longer alkyl chains showed higher capacities with an increasing amount of emulsifier. Concentrations of FSEY and its esters in the water phase decreased from 97.52% to 0.00% as the alkyl chain length increased in the binary oil-water system. Meanwhile, content of ester modified with hexyl chain increased upon the addition of emulsifier. Our finding suggest that modification through alkylation can alter the distribution patterns of peptide FSEY and its esters, leading to an enhanced antioxidant effect in the oil-in-water emulsion.