EFFECT OF PHOSPHOLIPASE A1ON THE PHYSICOCHEMICAL AND FUNCTIONAL PROPERTIES OF HEN'S EGG YOLK, PLASMA AND GRANULES

Assessing the structural and foaming property changes in egg yolk proteins due to malondialdehyde: Experimental and molecular docking studies

This study evaluated the effects of varying levels of malondialdehyde (MDA) on the structural and foaming properties of the egg yolk proteins (EYPs), and the interaction between them was explored by molecular docking. The results showed that oxidative modification due to MDA increased the carbonyl content of EYPs by 4.49 times. Simultaneously, the total sulfhydryl content was reduced by 21.47%, and the solubility of EYPs was significantly decreased (p < 0.05). Continuous oxidation disorders the previously ordered structure of EYPs. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated that some proteins underwent crosslinking and aggregation with increased MDA oxidation, aligning with changes in particle size and zeta-potential. Moderate oxidation (<1 mmol/L) enhanced the foaming capacity and foam stability of EYPs. Additionally, molecular docking results uncovered favorable interactions between MDA and specific EYPs, primarily through hydrogen bonding. This research offers valuable insights into managing the functional and quality changes of yolk products during processing.

Effect of high-hydrostatic pressure on the digestibility of egg yolk and granule

The impact of high hydrostatic pressure (HHP) on protein digestibility of egg yolk and egg yolk granule was evaluated by static in vitro digestion using the standardized INFOGEST 2.0 method. The degree of hydrolysis (DH) and the phospholipid content were determined during digestion, and the protein and peptide profiles were characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and reverse phase-high pressure liquid chromatography (RP-HPLC). The results showed that HHP induced protein aggregation in egg yolk and granule, mainly by disulfide bridges, which were not disrupted in the oral phase. Proteolysis during the gastric phase improved egg yolk and granule protein solubility, regardless of whether HHP was applied. However, the extent of the samples' digestibility was not affected, with DH values ranging from 15% to 20%. During the intestinal phase, the DH of egg yolk protein (∼40%) was higher than that of the granule (∼25%), probably due to the denser structure of the granule reducing the accessibility of intestinal enzymes. The DH, peptide, and protein profiles of control and HHP-treated egg yolk showed similar protein digestion behaviors for both gastric and intestinal phases. Among the different proteins, only the digestibility of β-phosvitin in HHP-treated granule was enhanced. Consequently, applying HHP to granules represents an interesting process that improves the digestibility of phosvitin with the potential to generate bioactive phosvitin-derived phosphopeptides. PRACTICAL APPLICATION: High hydrostatic pressure, mainly used as a preservation process, did not impair the nutritional quality of the egg yolk and granule proteins but improved the susceptibility of phosvitin (protein contained in egg yolk) proteolysis to produce bioactive phosphopeptides. Consequently, applying HHP to granules represents an interesting process that improves the digestibility of phosvitin.

Effect of Lipase and Phospholipase A1 on Foaming and Batter Properties of Yolk Contaminated Egg White

Egg white (EW) is frequently used in bakery products because of its excellent foaming capabilities. However, egg yolk (EY) contamination often degrades the foaming characteristics of EW. The purpose of this study was to investigate the effect of different concentrations of phospholipase A1 (PLPA1) and lipase (LP) on EW. The changes in particle size distribution and potential before and after enzymatic digestion of EW with contaminated 0.5 wt% and 1.0%wt EY were tested. The foaming rate and foam stability were measured after the dispersions were digested with different concentrations of PLPA1 and LP. Additionally, the dispersion samples were used to prepare batter and angel cake, and the modulus, density, and microstructure of the batter were analyzed. Results showed that the potential absolute value increased when the EY was hydrolyzed by PLPA1. The distribution of yolk particle size showed a new aggregation and the average particle size decreased after LP hydrolysis. The dispersion samples hydrolyzed by PLPA1 and LP recovered all the properties of the samples at enzymatic concentrations of 500 U/g and 2500 U/g. This may be attributed to the changes in yolk particles resulting from the enzymatic digestion of EY and the production of amphiphilic lysophospholipids, fatty acids, and glycerol.

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.

Effect of Phospholipase A1 and High-Pressure Homogenization on the Stability, Toxicity, and Permeability of Egg Yolk/Fish Oil Emulsions

Enzymatic treatment of egg yolk with phospholipases can enhance its emulsifying properties and thermal stability. Additionally, a two-step process (primary and secondary homogenization) could form emulsions with better stability. Thus, in this study we used a split-split-plot in time design to assess the effect of enzymatic treatment, processing, and storage conditions on the encapsulation efficiency, stability, toxicity, and permeability of egg yolk/fish oil emulsions stored up to 10 days at 45 °C. Egg yolk solutions before and after treatment with phospholipase A₁ were used as carriers of fish oil containing ≥82% eicosapentaenoic and docosahexaenoic acids. Emulsions were formed by primary (24,000 rpm, 4 min) and secondary (200 MPa) homogenization. The combined effect of treatment with phospholipase A₁ and secondary homogenization resulted in emulsions with improved stability, increased the encapsulation efficiency of the carriers, and reduced the release of oil to the particle surface, resulting in lower formation of oxidation products. At the end of storage time, none of the emulsions were toxic to Caco-2 cells at a concentration of 75 μg/mL medium, while nonencapsulated fish oil reduced cell viability to 81%. Only eicosapentaenoic acid was detected in the basolateral side of Caco-2:HT29 monolayers, and its apparent permeability from nonencapsulated fish oil was significantly lower than that from emulsions.

Effects of degree of hydrolysis (DH) on the functional properties of egg yolk hydrolysate with alcalase

Effects of enzymatic hydrolysis on the physicochemical and functional properties of egg yolk were investigated in this study. Alcalase, neutrase and flavourzyme were used to hydrolyze egg yolk. Solubility, foaming properties, emulsifying and microstructure properties of egg yolk were determined after enzymatic hydrolysis. Results showed that alcalase had better efficiency of hydrolysis than neutrase and flavourzyme. Enzymatic hydrolysis caused a marked changes in protein solubility, surface hydrophobicity, molecular weight distributions, microstructure and other functional properties. It was observed that egg yolk and its hydrolysates exhibited a relatively smooth curve over the entire pH range; egg yolk hydrolysates with high DH had higher solubility than those having lower DH. Foam capacity and stability generally increased with increasing DH although foam stability showed a decrease at 15% DH. Hydrolysates of egg yolk showed scattered and fewer aggregated particles. This study demonstrated that egg yolk hydrolysates could be an excellent emulsifying agent for food and other applications.