Covalent conjugation of pumpkin seed protein induction by epigallocatechin-3-gallate: Structural formation, functional and in vitro digestion properties

Abstract

Pumpkin seed protein (PSP), a valuable byproduct of pumpkin seed oil extraction, is abundant in essential amino acids but exhibits weak functional properties, limiting its processing and application potential. This study aimed to evaluate the effects of covalent modification with epigallocatechin-3-gallate (EGCG) at varying concentrations on the structural, functional and in vitro digestion properties of PSP. Sulfhydryl and free amino acid content analyses, combined with sodium dodecyl sulfate-polyacrylamide gel electrophoresis, confirmed the formation of covalent complexes through C-S and C-N bond formation between EGCG and PSP. Upon binding with EGCG, the secondary structure of PSP was predominantly shifted from a β-sheet (from 40.70 % to 11.70 %) to a random coil (from 23.70 % to 46.80 %), accompanied by enhanced flexibility and a 52.59 % reduction in surface hydrophobicity. The solubility of the PSP-EGCG covalent complexes increased by 66.07 %, while the maximum emulsifying activity reached 421.91 m²/g. However, protein digestibility decreased by up to 25.50 % with higher EGCG concentrations. These findings provide a theoretical foundation for improving PSP properties and applying its complexes in specialised functional foods.