Transglutaminase cross-linking to enhance elastic properties of soy protein hydrogels with intercalated montmorillonite nanoclay

To strengthen the network of bio-nanocomposite hydrogels, layered montmorillonite (MMT) nanoclay was intercalated by surface-coating with soy protein (SP) before mixing with 6% w/v SP for cross-linking by microbial transglutaminase (mTGase). Dynamic rheology was performed to study variables of NaCl and mTGase concentrations, with and without 1% w/v MMT. Without mTGase, the highest storage modulus (G′) was observed at 100 mM for samples without MMT, which was twice of the highest G′ for samples with MMT, at 200 mM NaCl. With mTGase, a shorter gelation time and a stronger hydrogel were observed at a higher enzyme level. Overall, the non-gelling 6% w/v SP dispersion was transformed to a hydrogel with G′ of 1099 Pa after addition of 100 mM NaCl and 1% SP-coated MMT and treatments by 6.25 U/g-protein mTGase for 2 h and heating/cooling steps. The integration of surface-coating and mTGase cross-linking is promising to improve properties of the nanocomposite system.

► Transglutaminase effectively cross-linked soy protein in the continuous phase and on MMT surface.
► Dynamic rheology elucidated impacts of cross-linking and subsequent heating and cooling.
► Without mTGase, the highest G′ was observed at 100 and 200 mM, respectively, with and without MMT.
► With mTGase, a shorter gelation time and a stronger hydrogel were observed at a higher enzyme level.
► For the treatment with MMT and 100 mM NaCl, cross-linking by mTGase for 2 h improved G′ by >20 times.