Comparative Study on Foaming Properties of Egg White with Yolk Fractions and Their Hydrolysates

As an excellent foaming agent, egg white protein (EWP) is always contaminated by egg yolk in the industrial processing, therefore, decreasing its foaming properties. The aim of this study was to simulate the industrial EWP (egg white protein with 0.5% w/w of egg yolk) and characterize their foaming and structural properties when hydrolyzed by two types of esterase (lipase and phospholipase A2). Results showed that egg yolk plasma might have been the main fraction, which led to the poor foaming properties of the contaminated egg white protein compared with egg yolk granules. After hydrolyzation, both foamability and foam stability of investigated systems thereof (egg white protein with egg yolk, egg white protein with egg yolk plasma, and egg white protein with egg yolk granules) increased significantly compared with unhydrolyzed ones. However, phospholipids A2 (PLP) seemed to be more effective on increasing their foaming properties as compared to those systems hydrolyzed by lipase (LP). The schematic diagrams of yolk fractions were proposed to explain the aggregation and dispersed behavior exposed in their changes of structures after hydrolysis, suggesting the aggregated effects of LP on yolk plasma and destructive effects of PLP on yolk granules, which may directly influence their foaming properties.