Transglutaminase-induced crosslinking of sodium caseinate stabilized oil droplets in oil-in-water emulsions

•Addition of TGase to emulsions can lead the emulsion remaining fluid.•Addition of TGase to the emulsion can induce a sol-gel transition.•At high oil droplet concentrations droplet-droplet networks are formed.•At high protein concentrations protein-networks containing droplets are formed.

The present study established a better understanding of the gelling mechanism of a crosslinking enzyme (microbial transglutaminase) added to sodium caseinate (Na-Cas)-stabilized oil-in-water emulsions varying in droplet concentration and protein content. First, fine dispersed emulsions (5-60% (w/w) Miglyol; 2, 5, and 8% (w/w) aqueous Na-Cas) were prepared using a high pressure homogenizer. Second, microbial transglutaminase was added to Na-Cas-stabilized emulsions (37 °C, 15 h, pH 6.8) to initiate Na-Cas crosslinking. Texture profile analysis and rheological measurements indicated that at low protein concentrations droplet-droplet inter-crosslinking occurred above a critical oil volume concentration (coil > 0.6) yielding particle gels. There, strength of the droplet networks formed depended on oil droplet. At high Na-Cas contents, crosslinking of excess Na-Cas in the aqueous phase occurred and particle-filled continuous gels were formed instead. Theoretical calculations of mean distances between droplets and diffusion coefficients of droplets indicate that a certain probability of contact was required for microbial transglutaminase to be able to crosslink droplets.