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Incorporation of vegetable oils through pre-emulsification has received notable attention for delivering polyunsaturated fatty acids to emulsified-type meat products. The two important influencing factors of the rheological property of composite myofibrillar protein (MP) gel are emulsion droplet size and active or inactive interaction between interface and meat proteins. Incorporation of nonmeat protein emulsion (2% protein (w/w), egg-white protein isolate (EPI), porcine plasma protein (PPP), or sodium caseinate (SC)) with different droplet sizes (nano or macro) to a model of 2% MP gel was investigated in this research. The results of drop size measurement showed that 15,000 psi homogenizing could decrease the diameter of emulsion drop from macro- to nanoscale in the range of 324.4–734.5 nm. Active fillers (PPP and EPI emulsions) with nanodroplet size did not influence the viscosity of emulsion-filled composite cold sols but caused positive filling effects on the MP gel matrix after heating, as evidenced by the density microstructure. PPP and EPI nano-emulsion-filled composite MP had a significant high storage modulus enforcement effect, which reached nearly eight times those of other treatments (p < 0.05). Similarly, the results of thermal scanning rheology and a large-deformation mechanical test showed that PPP and EPI emulsions with nanoscale droplets, other than macroscale, had the highest gel strength of heat-induced emulsion-filled composite MP gel (p < 0.05). Overall, these findings will be helpful for selecting the correct pre-emulsified protein and designing the textural properties of foods.

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Protein conformational rearrangement triggered by adsorption to the hydrophobic interface of oil droplets has long been considered as a key factor in emulsification. In this study, an alkaline pH-shifting-driven conformational adaptation enhanced interfacial proteins was used to improve their stability against heat-induced flocculation of myosin emulsions. We used the unfolded myosin at pH 12 to emulsify soy oil and then readjusted the pH of the emulsion to neutral. The corresponding myosin emulsion (0.5% w/v protein, 10% v/v soy oil, and 0.6 M NaCl) almost not flocculated when heated at 75 °C for 30 min. Moreover, after thermal treatment, the particle size of the emulsion was not significantly increased (P > 0.05) and the emulsion did not exhibit a creaming phenomenon after a week. Based on the circular dichroism and Fourier transform infrared analysis, we speculated the superiority of the emulsion is closely related to the alkaline pH-shifting-driven conformational adaptation enhanced interfacial protein. Additionally, the resulting steric stabilization in overcoming the attractive hydrophobic forces between denatured protein molecules coated droplets might be the main factor for the inhibition of heat-induced flocculation of the emulsion. Our research may have important implications for the formulation of protein-stabilized oil-in-water emulsions.

Soluble aggregates, instead of insoluble gel network, were formed on heat-treated chicken breast myosin through alkaline pH-induced electrostatic regulation. Heat treatment of myosin at pH 9.0 significantly increased solubility, decreased turbidity, and resulted in the highest content at 260 nm particle size compared with those at pH 7.0 and 8.0. Results indicated that soluble myosin aggregates were produced at pH 9.0. The surface hydrophobicity and reactive sulfhydryl (R-SH) of unheated sample revealed gradual increases with increased pH. This increase was related to the decreased α-helical, thereby suggesting myosin unfolding. After heating, treatment at pH 9.0 showed the lowest surface hydrophobicity and R-SH, which may contribute to the highest dispersibility. Moreover, heated myosin (pH 9.0) after reshifting pH still exhibited excellent stability, which indicated the irreversible soluble aggregates formation. The controlled production of aggregates may provide the possibility of using soluble aggregates as ingredients for expanded meat protein application in beverage products.Agregación térmica alcalina dependiente del pH de miosina de pechuga de pollo: formación de agregados solubles RESUMEN En el presente estudio se formaron agregados solubles -en vez de una red de gel insoluble-a partir de la miosina de pechuga de pollo tratada térmicamente mediante regulación electrostática alcalina inducida por el pH. En comparación con tratamientos a un nivel de pH de 7.0 y 8.0, el tratamiento térmico de miosina con un pH de 9.0 aumentó significativamente su solubilidad, disminuyó su turbidez y produjo el contenido más alto, obteniéndose partículas de un tamaño de 260 nm. Los resultados indican que se formaron agregados de miosina solubles a un nivel de pH de 9.0. En la muestra no sujeta a tratamiento térmico, la hidrofobicidad superficial y el sulfhidrilo reactivo (R-SH) mostraron incrementos graduales al elevarse el pH. Este aumento está relacionado con la α-helical disminuida, lo cual sugiere que tuvo lugar el desdoblamiento de la miosina. Tras el calentamiento, el tratamiento a un nivel de pH de 9.0 presentó hidrofobicidad superficial y R-SH más bajas, lo cual puede contribuir a la mayor dispersibilidad. Asimismo, después de variar el pH, la miosina calentada (pH 9.0) siguió exhibiendo una excelente estabilidad, lo que da cuenta de la formación irreversible de agregados solubles. La producción controlada de agregados puede dar pie al posible uso de agregados solubles como ingredientes para la aplicación de mayores cantidades de proteína cárnica en productos de bebidas.