Effect of enzymatic hydrolysis on the solubility of egg yolk powder from the changes in structure and functional properties

Egg yolk powder (EYP) is widely used in food processing due to its excellent emulsifying properties, but its poor solubility limits its market application as a powdered beverage. In this study, papain, trypsin, and subtilisin were used to hydrolyze egg yolk, and the effects of enzymatic hydrolysis on the solubility of EYP was investigated. The results showed that subtilisin treatment significantly improved the water dispersibility, powder solubility and stability coefficient of EYP (P < 0.05) by 41.67%, 98.16%, and 66.21%, respectively, while its solubility did not change significantly after the treatment with papain and trypsin. The degree of hydrolysis (DH) was related to the enzyme active site and the treatment with papain and subtilisin resulted in a higher DH. Additionally, the results of sodium dodecyl sulfate-polyacrylamide gel electrophoresis, particle size distribution and scanning electron microscopy proved that the molecular weight of subtilisin-treated EYP was lower than EYP after the other treatments. Moreover, surface hydrophobicity and zeta-potential results indicated that molecular hydrophobicity and the amount of surface charge increased after enzymatic hydrolysis. The hydratability of papain-treated EYP increased to 20.91%. Low-field nuclear magnetic resonance results showed that enzymatic hydrolysis changed the content of bound water in the EYP, resulting in the changes of its ability to combine with water.