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The inadvertent flow of mildly/moderately oxidized oil into production critically causes quality uncontrollability in food emulsions. In this paper, we explored the effects of oil pre-oxidation (oxidized before emulsification) on the emulsion stability and interfacial properties of two protein emulsifiers (myofibrillar protein, MP; sodium caseinate, SC). These effects were further found to be different dependent on the proteins native structural and physicochemical properties. For MP with a highly structured fibrous conformation, the adsorption capacity, diffusion and rearrangement rate, and dilatational elastic modulus were decreased (by at least 5.74%, 16.25%, 11.21%, 10.04% respectively) at the oxidized-oil/water interface, which were mainly explained by the increased oil polarity and the generated interfacial-active oxidation products that impeded the interfacial unfolding and protein-protein interactions. With an appreciably high adsorbed amount (adsorption ratio >90%), the MP's oxidized-oil emulsion stability was largely determined by the interfacial properties, and thus significantly decreased with oil oxidation (even at the mild oxidation level). In contrast, for SC with a disordered structure, the rearrangement rate and dilatational elastic modulus were similarly decreased (by at least 14.61%, 12.56% respectively) at the oxidized-oil/water interface, while the adsorption capacity and diffusion rate were increased (by at least 5.40%, 13.16% respectively) possibly due to the enhanced hydrogen bonding between the more hydrophilic SC and the higher polarity oil. With a significantly lower adsorbed amount (adsorption ratio <10%), the SC's oxidized-oil emulsion stability was mainly decided by the oil inherent properties but not interfacial performance, which thus significantly increased with oil oxidation (even at the mild level) due to the growing oil polarity and density. These findings highlight that mild oil pre-oxidation could have critical impacts on emulsion stability, and the mechanism exploration provides scientific guidelines for the quality control and rational formulation of labile unsaturated oil-based emulsion foods (e.g. fat substituted emulsified meat products). [Display omitted] • Oxidation increased oil polarity with the generation of interfacial-active products. • Oil pre-oxidation impaired MP emulsion stability but promoted SC emulsion stability. • Oil pre-oxidation impaired rearrangement rate, interfacial film strength of MP and SC. • Adsorption capacity and diffusion rate varied depended on protein properties. • Dispersed-phase and interfacial-film both mattered in affecting emulsion stability. [ABSTRACT FROM AUTHOR]

The effects of the oils density and viscosity (DV) on the emulsions kinetic stability and destabilization mechanisms were revealed from the perspective of droplets movement and emulsions viscosity. With the extension of storage time, severe creaming (20.20 ± 0.73 × 10−4 mm/s), flocculation and coalescence (7.26 ± 0.82 μm−2 min−1) occurred in emulsions prepared with oils of lowest DV; the extent of creaming (15.90 ± 0.68 × 10−4 mm/s) and coalescence (1.36 ± 0.10 μm−2 min−1) were alleviated upon increasing oils DV, accompanied by the occurrence of acute Ostwald ripening (17.03 ± 1.72 μm3 min−1); and only slight creaming (2.26 ± 0.24 × 10−4 mm/s), flocculation, coalescence (0.70 ± 0.09 μm−2 min−1) and Ostwald ripening (6.14 ± 0.42 μm3 min−1) occurred in emulsions prepared with oils of highest DV. This was because oils with higher DV (especially density) restricted the droplets fluidity due to an increased motion friction, leading to a more homogeneous internal network and a higher apparent/macroscopic viscosity (0.31 ± 0.04 Pa·sn and 0.1 nm−2 s) of emulsions. These impeded the Brownian motion and diffusion of droplets to decrease the collision frequency/efficiency and mass transfer respectively, which in turn conduced to retarding droplets size enlargement and stabilizing the emulsions against different destabilization mechanisms. [Display omitted] • Higher oil density and viscosity (DV) improves emulsions stability. • Oils of high DV increase the emulsion viscosity. • Oils of high DV retard gravitational separation to increase creaming stability. • Oils of high DV delay Brownian motion to increase flocculation/coalescence stability. • Density plays a more decisive role in tuning emulsions viscosity and stability. [ABSTRACT FROM AUTHOR]