Abstract
The emulsifying properties of egg yolk with diacylglycerol (DAG) as the oil phase were investigated and compared with triacylglycerol (TAG) as the oil phase. The fatty acids of the DAG and TAG samples were adjusted to nearly the same composition before being used in this experiment. The effects of egg yolk concentration, pH, and the added salt on the emulsifying properties were evaluated by the interfacial tension, flow characteristics, oil droplet size and emulsifying capacity of the emulsion.
The interfacial tension in the TAG-egg yolk solution interface decreased significantly depending on the concentration of the egg yolk. The decrease was most marked at pH 6, and at pH 3 and 9 albeit to a lesser extent. The decrease in interfacial tension of DAG was less than that of TAG and the differences associated with decreased pH were also small. The viscosity of the TAG emulsion (egg yolk 1%, oil volume fraction 0.5) was not largely affected by pH. DAG at pH 6 produced a high viscosity emulsion, but droplet size was not affected by sample oil and pH. The emulsifying capacity of both oil samples was markedly higher at pH 6 compared to pH 3 and pH 9, which was more conspicuous in TAG. While the addition of NaCl did not affect the interfacial tension of TAG, it decreased the interfacial tension and viscosity of emulsion of DAG. The emulsifying capacity of both TAG and DAG increased after the addition of NaCl, with the magnitude of the increase being larger in DAG.
