Improving sweet potato protein gel properties through ε-(γ-glutamy)-lysine isopeptide cross-link catalyzed by transglutaminase

Production of sweet potato protein (SPP) gels with enhanced viscoelasticity and mechanical properties through transglutaminase (Tgase) catalyzed SPP ε-(γ-glutamy) - lysine cross-link was investigated. Tgase induced cross-link of SPP increased the protein molecular weight, and slightly reduced its gelling point. Gel viscoelasticity was significantly enhanced with the maximum storage modulus (Gʹmax) increasing from 2,990 Pa to 30,700 Pa as Tgase concentration increased from 0% to 5.0%. The exponent (zʹ) of the power law (Gʹ = kʹωzʹ), decreased from 0.024 (control SPP gel) to zʹ in the range 0.018–0.022 for the SPP ε-(γ-glutamy) - lysine cross-link (SPP – GL) gels. SPP gel network structure showed increased covalence interaction with increase in the level of Tgase induced cross-linking. SPP gel had no fracture stress but suffer deformation under little stress, while SPP – GL cross-linked gels formed with 1.6, 3.2 and 5.0% Tgase could withstand higher stress and had fracture stress and strain in the range 97.3–235.5 kNm−2 and 0.065–0.448 respectively. Tgase induced SPP ε-(γ-glutamy) - lysine cross-link enhanced SPP gel hardness, resilience and adhesiveness.