Extraction and Characterization of Lysozyme from Salted Duck Egg White

Bioactives derived from egg by-products: Preparation, health benefits, and high-value-added applications

Eggs are widely known for their rich nutritional profile, resulting in the production of numerous egg by-products. Recycling of egg by-products has become a key for achieving sustainable development. This work reviews recent advances on preparation of bioactives derived from egg by-products and their health benefits from the perspective of by-product valorization. Meanwhile, the potential for high-value-added applications of egg by-products is discussed. Egg by-products contain bioactives (proteins, minerals, glycosaminoglycans, and bioactive peptides) with various health benefits, including antioxidant, anti-inflammatory, metal ion-chelating, and protective activity against metabolic syndrome, but mechanisms behind these phenomena are still unclear. Therefore, combination of multiple models and multiple omics to reveal functional mechanisms of the bioactives is imperative, and further clinical trials are necessary to evaluate their bioaccessibility. Additionally, research on the product formulation based on egg by-products or their derived bioactives could expand the valorization of the by-products and contribute to global sustainable development.

Separation of Lysozyme-Ovotransferrin Complexes and the Cooperative Role of Their Components in Egg White

A complex of ovotransferrin and lysozyme was directly isolated from egg white using an anti-transferrin antibody-immobilized membrane after antiserum proteins were separated by non-denaturing two-dimensional electrophoresis and transferred onto a membrane. The complex retained lysozyme activity that catalyzes the breakdown of peptidoglycans in the bacterial cell wall at the β1-4 bond between N-acetylmuramic acid and N-acetylglucosamine residues. The activity of the purified lysozyme was suppressed to 6.4% in the presence of 1 μmol Fe2+, whereas that of the mixture of the purified lysozyme and ovotransferrin was maintained at 58%. The activity of the purified lysozyme was suppressed to 35% in the presence of 10 nmol Fe3+, whereas that of the mixture of the purified lysozyme and ovotransferrin was maintained at 66%. Furthermore, the bacteriolytic activity against Bacillus subtilis of egg white with reduced glycoproteins such as ovotransferrin was assessed, and the bacteriolytic activity was found to be suppressed in the presence of Fe2+ and Fe3+. This suppression was ions, thereby alleviating the inhibition of lysozyme activity by iron ions. A complex of ovotransferrin and lysozyme is efficient because ovotransferrin effectively captures iron ions near lysozyme. Thus, protein complexes containing enzymes can be applied to control their activity.

Dietary supplementation of lysozyme can improve growth rate, laying performance, blood biochemistry, and mRNA levels of some related genes in different plumage-colored quails

The impact of dietary lysozyme (LZ) supplementation on the growth and laying performance was investigated over 4 weeks of growing and 6 weeks of laying periods in two different plumage color (white and brown-feathered) Japanese quail varieties. For each variety, 240 birds were randomly assigned into four groups with four replicates for each group. The first group (control) was fed a basal non-supplemented diet (BD). Whereas the 2nd, 3rd, and 4th received the BD supplemented with commercial LZ (CLZ) at 100 mg/kg diet, and natural LZ (NLZ) at 100 and 200 mg/kg diet, respectively. The main findings included significant increases in body weights and gains in the white-feathered quails supplemented with NLZ1 compared to the control and NLZ2. However, there were no significant differences in the case of brown-feathered quails in all LZ supplementations. Moreover, the different dietary LZ lowered FI in both quails with the lowest intake observed in the brown-feathered quails. Accordingly, enhanced FCR was reported in the CLZ groups for both quail varieties and in NLZ1 and NLZ2 for the white-feathered and brown-feathered quails, respectively. In both quail varieties, the NLZ2 significantly lowered serum creatinine and urea and increased albumen and globulin levels compared with other groups. Histologically, the best hepatic histological features were found in both quail' varieties fed the NLZ1-supplemented diet. Accompanying LZ-induced modulations in the expression levels of GHR, IGF-1, leptin, CCK, FAS, and ACC genes in both quail varieties were reported. Besides, both quail varieties in NLZ1& NLZ2 supplementation exhibited significant increases in hen day egg production, egg weight, egg mass, and hatchability percentages along with differences in external and internal egg qualities compared with LZ-free diet or CLZ. Therefore, NLZ could be used as an effective feed supplement to enhance the growth and egg performance of Japanese quail with caution being drawn to the supplementation dose about quail variety.

A novel thermophilic lysozyme 4356 from Cohnella sp. A01: Cloning, heterologous expression, biochemical and kinetic characterization

Lysozymes have gained attention for their antiseptic properties. In silico studies have shown that the enzyme containing lysM can act as an antibacterial agent. Binding of the lysM motif of rSELys to peptidoglycan and molecular dynamics simulations showed that the protein-ligand binding is very stable. rSELys (2016 bp) is a new recombinant glycoside hydrolase from the thermophilic bacterium Cohnella sp. A01 (PTCC number: 1921). Protein expression and purification, a single band with an apparent molecular weight of ∼74 kDa was observed by SDS-PAGE. The kinetic parameters were Km 1.163 mg/ml, Vmax 670.3 U/mg, kcat 1675.75 (S-1), and kcat/Km 1440.88 (M-1S-1). Its optimum temperature was 55 °C and pH 8. Temperature stability also showed that the temperature of 50-60 °C retained more than half of its activity after 90 min. Based on the results, rSELys demonstrated antibacterial effects on both Gram-positive and Gram-negative strains, with inhibition zones of 11 and 9 mm, respectively. SEM analysis confirmed hydrolysis activity, the MIC was determined to be 31.25 μg/ml and 3.9 μg/ml, and MBC 0.97 μg/ml, respectively. CD and fluorescence studies showed that up to a temperature of 85 °C and a pH value of 8-12 no structural changes occur, and thermal stability protein was confirmed.

Quality characteristics, lysozyme activity, and albumen viscosity of fresh hatching duck eggs after a week's storage at various temperatures

The study aimed to analyze the qualitative features of Cherry Valley duck' hatching eggs during storage at different temperatures. Eggs were divided into 3 equal groups with 30 eggs each: fresh egg and stored at 7 °C and 17 °C within one week. Qualitative analyses of duck eggs were carried out, considering the morphological composition, physicochemical characteristics, lysozyme activity, and albumen viscosity. The highest weight of yolk and its percentage was found in the 17 °C group. The weight and percentage of albumen were significantly the highest in the group of fresh eggs. Higher egg weight loss was observed in the group stored at higher temperatures. Higher thick albumen height and Haugh units were found in fresh eggs and eggs stored at 7 °C. Different temperatures of egg storage did not affect lysozyme activity in thick and thin albumen. Stored eggs were characterized by lower albumen viscosity only at a shear rate of 10 rpm. The higher viscosity of thick albumen compared to thin ones was demonstrated at 10 and 20 rpm shear rates. The presented research results indicate a large diversity of selected qualitative indicators of hatching duck eggs, which may affect their storage and suitability for incubation.

High gelatinous salted duck egg white protein powder gel: Physicochemical, microstructure and techno-functional properties

Salted duck egg is one of the most popular products, and China is one of the major countries consuming salted duck egg products. However, due to the high salt content of salted egg white and low physical and chemical properties such as gel, many factories generally only use salted egg yolk and discard salted duck egg white (SDEW) as a waste liquid when processing. This is not only a waste of resources, but also a pollution to the environment. In this paper, protein powder was prepared from salted egg white. Then xanthan gum (XG) was added to make it co-gel with ovalbumin to achieve the purpose of preparing high gelatinous salted egg white protein powder. The results showed that the optimum conditions of SDEW-XG composite gel were as follows: the xanthan gum content was 0.08% (w/w), the reaction pH was 6.5, and the heating temperature was 100°C. Under these conditions, the gel strength reaches the maximum value. Meanwhile, compared with the protein powder without xanthan gum, the addition of xanthan gum significantly affected the secondary structure of the protein powder of SDEW and improved the water holding capacity of the gel. In conclusion, the addition of xanthan gum can significantly improve the gel quality of SDEW protein powder, which provides a theoretical basis for the quality improvement of salted egg white.