Investigations into aggregate formation with oppositely charged oil-in-water emulsions at different pH values

The pH-dependent formation and stability of food-grade heteroaggregates from oppositely charged oil-in-water (O/W) emulsions was investigated. After screening suitable emulsifiers, 10% (w/w) oil in-water emulsions (d32 ≈ 1 μm) were prepared at pH 3–7 using a positively charged emulsifier (Na-lauroyl-l-arginine ethyl ester; LAE) and four negatively charged ones (citric esters of mono- and diglycerides, soy lecithin, sugar beet pectin, and Quillaja saponin). The oppositely charged emulsions were then combined at constant pH values at a volume flow rate ratio of 1:1. Emulsions and heteroaggregates were characterized by their surface charge, particle size distribution and microstructure using dynamic and static light scattering as well as confocal laser scanning microscopy. The emulsifier type was found to greatly influence the type of heteroaggregates formed, as well as the pH value, specifically in combined LAE/Quillaja saponin emulsions. Larger aggregates particularly were formed with increasing pH values (2.71 ± 1.21 to 46.53 ± 4.30 μm from pH 3 to 7, respectively), while LAE/pectin aggregates appeared not to be affected by pH over the full pH range investigated (3.80 ± 2.89 to 3.94 ± 2.78 μm from pH 3 to 7, respectively). Our study thus provides valuable first insights into the mechanism of the formation of food-grade heteroaggregates for later use in food systems.