Assembling of the interfacial layer affects the physical and oxidative stability of faba bean protein-stabilized oil-in-water emulsions with chitosan

This study investigated how different ways of assembling of faba bean protein isolate (FBPI) and chitosan (CH) affected the oil-in-water emulsion stability. Emulsions were prepared either by a soluble FBPI-CH complex to make EMC, or by FBPI first and then added non-interactive CH to make EMN, or by FBPI first and then added a secondary layer of CH via electrostatic attraction to make EML. A control emulsion EMFB was prepared by only FBPI. All emulsions contained 5% (w/v) oil and 0.5% (w/v) FBPI. EMC/EML/EMN contained 0.05% (w/v) CH. The emulsion stability was monitored at 37 °C for 7 days. EML not only showed better physical stability as indicated by the changes in droplet size, Turbiscan stability index, and microstructure (by confocal microscopy), but also exhibited superior oxidative stability as indicated by lipid oxidation products (less conjugated dienes and secondary oxidation products) and protein oxidation biomarkers (less tryptophan loss and carbonyls formation). This might be attributed to that CH enhanced formation of a layer-by-layer (LBL) interfacial structure, which increased the interfacial layer thickness/compactness and maintained the interfacial protein adsorption. In contrast, EMC demonstrated worse stability, albeit with thicker interfacial layer due to CH. This could be explained by the lower surface hydrophobicity and surface charge of soluble FBPI-CH complex. The free aqueous CH also impaired physical stability and promoted oxidation, as shown in EMN. In conclusion, CH improves the oxidative and physical stability of FBPI-containing emulsion when added as a LBL model.