Transglutaminase crosslinked fish gelatins for emulsion stabilization: From conventional to Pickering emulsions

Gelatin-stabilized emulsions, including conventional and Pickering emulsions, are gaining popularity. In this study, fish gelatins (FG) were modified with transglutaminase (TG) to prepare gelatin molecules, microgels, and their mixtures. The transition of emulsions from conventional to Pickering was observed as gelatins evolved from molecules to microgels. FG (3%) was cross-linked with TG at 0–30 U/g. FG evolved from gelatin molecules into thermo-irreversible hydrogels as TG increased. Without TG or at a low level of TG (10 U/g), FG mainly existed as gelatin molecules that were liquid at 25 °C. At high levels of TG (20 or 30 U/g), FG crosslinked and developed thermo-irreversible chemical hydrogels that were solid. As the concentration of TG increased, the protein molecular weights, zeta potentials, and surface hydrophobicity were significantly increased. Microfluidization was employed to prepare gelatin microgels. Different states of gelatins were mixed with sunflower oil to prepare conventional emulsions, Pickering emulsions, and mixtures. With increased TG, the emulsion droplets became more homogeneous, and protein networks formed around the oil droplets. Emulsions stabilized with modified FG displayed improved physical stability than those stabilized with unmodified FG. At 10 °C, the emulsions stabilized by a mixture of FG molecules and microgels presented higher physical stability. At 25 °C, Pickering emulsions stabilized by microgels showed improved anti-coalescence. The results of this work could provide valuable references for applying gelatin-stabilized conventional or Pickering emulsions with tunable properties, hence increasing the formulation flexibility of gelatin-based food products.