Olive oil-in-water emulsions stabilized with caseinate: Elucidation of protein–lipid interactions by infrared spectroscopy

This paper reports a FT-IR study for probing lipid and protein structural changes and their interactions in various oil-in-water emulsions. Two different emulsions were prepared using sodium caseinate, as stabilizer system, without and with microbial transglutaminase (MTG), denominated E/SC and E/SC + MTG respectively. Proximate composition, fat and water binding properties and textural characteristics were also evaluated in the emulsions. Penetration force and gel strength values were used to distinguish different (P < 0.05) textural behaviours depending on the formulation of emulsifying system. E/SC + MTG emulsion showed gel textural behaviour while E/SC lack of this property. The spectral results showed frequency upshifting of the amide I band in going from protein stabilizer systems isolate (the solution used as reference) to their corresponding emulsions, what is attributable to greater protein structural order upon emulsion formation. Enzymatic action of MTG in the sodium caseinate stabilizing system induces structural changes, in terms of lipid chain disorder or lipid–protein interactions and protein secondary modifications, which may reflect the formation of a gel structure in the emulsion. These results could help to choose the stabilizing system that is most suitable and effective for its use in the formulation of food products.

Graphical abstractInfrared spectroscopy (FT-IR) can be used to provide information about lipids and protein structures and their interactions in olive oil-in-water emulsion. The extent of lipid chain disorder or lipid–protein interactions in emulsion depends on the formulation of the stabilizing system. In particular, the emulsion made with a mixture of sodium caseinate and microbial transglutaminase exhibited the greatest lipid chain disorder (or lipid–protein interactions) and the greatest protein structural changes as compared with the pure protein emulsifying system in aqueous solution. These structural changes in lipids and proteins were accompanied by the greatest gel strength.Figure optionsDownload full-size imageDownload as PowerPoint slide