Effect of enzymatic hydrolysis on heat stability and emulsifying properties of egg yolk

Abstract Egg yolk is an indispensable ingredient in the preparation of food emulsions due to its unique nutritional value and functional properties. However, egg yolk is sensitive to heat treatment and has poor emulsifying stability, which can be a limitation to the application of egg yolk in food industry. This study, the effect of neutral and alkaline protease (2,000U/g egg yolk protein) on thermal stability and emulsifying properties of egg yolk was investigated. Results showed that the hydrolysed egg yolk had higher thermal stability and emulsifying stability, especially for the samples hydrolysed by alkaline protease. The molecular weight of hydrolysed egg yolk protein was smaller than others as proved by electrophoresis and a considerable increase of protein solubility was observed. In addition, hydrolysis changed the degree of ionization of amino acids, increasing its static charge. The smaller molecular weight of the protein and the higher electrostatic charge delayed the gelation point, improving the thermal stability of the egg yolk. The emulsifying stability of hydrolysed egg yolk was improved, possibly resulting from the increase of soluble protein or polypeptide. Emulsions made with hydrolyzed egg yolk exhibited smaller particle sizes and higher surface charges, thus improving creaming stability of emulsions.