Rheological and stability properties of gelatin, starch, or chitosan coating-forming solutions incorporated with O/W emulsions encapsulating rutin, carvacrol, and α-tocopherol

Abstract This study investigated the rheological properties and physical stability of gelatin (Ge), starch (St), and chitosan (Ch) coating-forming solutions (CFSs) incorporating conventional emulsions (CE), nanoemulsions (NE), and Pickering emulsions (PE) encapsulating rutin, carvacrol, and α-tocopherol. CE and NE were prepared using soybean oil, Span 80/Tween 80, water, and active compounds. CE additionally contained soybean lecithin. PE were produced with soybean oil, soybean lecithin, active compounds, and previously prepared chitosan particles. CFSs were obtained by solubilization and heating for Ge, gelatinization for St, and acidification to pH 4.5 for Ch. Chitosan particles showed a modal size of approximately 846 nm. CE and NE exhibited bimodal droplet-size distributions. PE showed a trimodal profile, reflecting particle-related structuring. Soy lecithin contributed to high Zeta-potential values in CE and PE. Stability analysis revealed creaming in CE, early destabilization in NE with low transmission, and very low transmission in PE. This indicated a highly structured system. All emulsions were pseudoplastic, with NE showing the strongest shear-thinning behavior. After incorporation into CFSs, the effects were strongly matrix-dependent. Ge-CFSs behaved as Newtonian systems, whereas St- and Ch-CFSs were pseudoplastic. Emulsion addition increased the viscosity of Ge-CFSs. Frequency sweeps classified Ge systems as gel-like, the St systems as liquid-like, and the Ch systems as viscoelastic. Overall, the emulsion interfacial design was not preserved upon incorporation into CFSs. Instead, flow and stability were primarily governed by emulsion–matrix compatibility. Graphical Abstract