The influence of pH-induced structural modifications of myofibrillar proteins (MPs) on their interaction mechanisms with pyrazine compounds was investigated. At a lower pH (4.9, 5.5), MPs aggregated to larger particle sizes due to enhanced the protein–protein interactions. The binding with pyrazine compounds was strongly affected by pH and the nature of flavor compounds. MPs exhibited flavor releasing behavior, probably due to protein–protein interactions and surface tension. Fluorescence analysis revealed that the interaction of pyrazine compounds with MPs followed a combination of static and dynamic quenching. The changes in quenching constant ( K sv ) might be attributed to a dynamic quenching, probably due to protein aggregation. The percentages of free 2,5-Dimethylpyrazine (2,5-DMP) were similar to K sv . Thermodynamic parameters indicated that electrostatic interactions and hydrophobic interactions were the major acting forces in the binding of MPs to 2,5-DMP. The binding of 2,5-DMP increased the α-helix content of MPs.
The oil polarity was hypothesized to significantly influence the microscopic conformation of interfacial myofibrillar protein (MP) and thus the mesoscopic interfacial rheology of MP film , which ultimately tuned the macroscopic stability of MP-stabilized emulsions. In this research, the inner mechanism was revealed hierarchically based on emulsions multi-scale properties, by a combination of in vitro interfacial concentration measurement, dynamic interfacial tension measurement and interfacial dilatational rheology (highlighting Lissajous plots). Then, the above conclusion was verified through in silico molecular dynamic simulation. At macroscopic level, the light scattering results showed that emulsion prepared with higher polarity oil exhibited higher physical stability. This could be explained from the mesoscopic perspective that: (1) the adsorption dynamics of MP was faster (though lower diffusion rate, but higher penetration and rearrangement rate) on the higher polarity interface, which decreased interfacial tension more efficiently; (2) adsorption ratio, surface load and desorption ratio indicated that ‘multilayer interfacial film’ was formed by loosely-bound MP on the lower polarity interface, which decreased the effective interfacial coverage to impair emulsions stability; (3) Lissajous plots showed that interfacial structure with higher stability against large deformation was formed on the higher polarity oil interface. Finally, the microscopic molecular mechanism for explaining the above findings was revealed by in silico molecular dynamic simulation: though MP was less unfolded on the higher polarity interface leading to weaker intermolecular hydrophobic interactions, this compact molecular structure with stronger intramolecular rigidity predominantly contributed to steadier interfacial film structure. This multi-scale study provides a deep insight into the inner relationship between oil polarity and emulsions stability.
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