Concentration-dependent effects of ε-poly-L-lysine as an amine nucleophile in microbial transglutaminase-catalyzed gluten modification: structural, rheological, and antimicrobial insights

Gluten is essential to the rheological and functional properties of wheat dough. Microbial transglutaminase is often used to enhance gluten functionality through cross-linking and, when combined with amine nucleophiles, can reduce its immunogenicity. ε-Poly-L-lysine (ε-PL), a GRAS-status natural homopolymer of lysine with antimicrobial activity, can efficiently act as an amine nucleophile for transamidation, yet its effects on gluten microstructure and rheology remain unexplored. This study investigates the concentration-dependent impact of covalently linked ε-PL on gluten structure and functionality. Polymeric structure was analyzed using asymmetric flow field-flow fractionation, and rheological behavior was evaluated through small and large deformation tests. A preliminary antimicrobial assessment was also conducted. At a 1:1 ε-PL:glutamine molar ratio, protein polymer size and resistance to extension increased, indicating a reinforced gluten network due to enhanced cross-linking. In contrast, a 5:1 ratio reduced polymer size and elasticity while enhancing extensibility, consistent with a plasticizing effect. These findings demonstrate that ε-PL modulates gluten structure and mechanics in a concentration-dependent manner. Moreover, ε-PL incorporation reduced yeast viability, suggesting added antimicrobial potential. Overall, this work provides new insights into ε-PL-mediated transamidation as a strategy to tailor gluten polymerization, dough rheology, and microbial stability. • Covalently linked ε-PL modulates dough structure and mechanical strength • 1:1 ε-PL:Gln ratio increases protein polymer size and force characteristics • 5:1 ε-PL:Gln ratio reduces elasticity but enhances dough extensibility • ε-PL incorporation reduces yeast viability, showing antimicrobial potential • Findings support enhanced gluten functionality and extended shelf life in foods