One-step in-situ fabrication of novel food-grade Janus droplets with zein and alginate: Dual effect of phase separation and interfacial equilibrium

Janus droplets exhibit an asymmetric structure, where one droplet has two compartments with different properties. However, food-grade Janus droplets are rarely reported. In this work, food-grade Janus droplets composed of alcohol-soluble protein and alginate were fabricated for the first time by the one-step in-situ method. Segregative phase separation and interfacial equilibrium of zein and alginate solutions were the prerequisites for the formation of food-grade Janus droplets. Segregative phase separation occurred when the concentration of zein and alginate solutions was increased. The zein in the aqueous phase synergistically reduced the oil-water interfacial tension with polyglycerol polyricinoleate (PGPR), but the alginate weakened the interfacial ability of PGPR, resulting in an increase of oil-water interfacial tension. Therefore, the interfacial tension difference between zein/oil and alginate/oil could be regulated by changing the concentration of zein and alginate solutions, which was beneficial to the interfacial equilibrium. The droplet size of food-grade Janus droplets could be adjusted by the concentrations of zein and alginate solutions. In addition, the Janus droplet structure could be further controlled by the volume ratio of zein and alginate solutions. The destabilization of food-grade Janus droplets was dominated by coalescence and sedimentation. The construction of food-grade Janus droplets is expected to provide a structural basis for the construction of food-grade Janus particles and promote the development of food technology.