Egg White Ovomucin Shows Anti-Adhesive and Anti-fouling Properties

• Author / Creator

  Sun, Xiaohong

• Ovomucin, a member of mucin family, is a glycoprotein accounting for 2-4% of egg white protein. Ovomucin is rich in sialic acid (2.6-7.4%, w/w), which has been suggested as an essential nutrient for infants. Ovomucin is insoluble at neutral pH or in the absence of denaturing agents. The overall objective of this thesis was to explore the potential of egg white ovomucin as value-added anti-adhesive and anti-fouling ingredients. To improve ovomucin’s water solubility, ovomucin was hydrolyzed by various proteases with yields and degree of hydrolysis (DHs) ranged from 42.6% (flavourzyme) to 97.4% (protease N), and 2.4% (flavourzyme) to 46.3% (pronase), respectively. Ovomucin hydrolyzed by pronase and protex 26L showed molecular weight (Mw) distribution less than 40 kDa while the others with Mw larger than 200 kDa. Allergenicity of all ovomucin hydrolysates was significantly reduced (P<0.05) in comparison to ovomucin extracts. The content of sialic acid in hydrolysates ranged from 0.1% (protex 26L) to 3.7% (pronase). The anti-adhesive potential of ovomucin/ovomucin hydrolysates was firstly determined by hemagglutination assay (HA). HA results demonstrated that ovomucin hydrolysates, but not intact ovomucin, prevented two K88 enterotoxigenic Escherichia coli (ETEC) strains adhesion to porcine erythrocytes. Ovomucin hydrolysate prepared by acid protease II exhibited the best anti-agglutinating activity against both ETEC strains; this hydrolysate was fractionated by cation exchange chromatography and reverse-phase HPLC. The most active fractions, F3(9) and F7(1), with minimal inhibitory concentration of 0.03 g/L and 0.25 g/L, against strains ECL13795 and ECL13998, respectively, were subjected to structure characterization. Six glycopeptides identified were all derived from α-ovomucin, composed of a pentasaccharide core of two N-acetylglucosamine and three mannose residues (GlcNAc2Man3) and a bisecting N-acetylglucosamine (GlcNAc). The anti-adhesive activity of ovomucin hydrolysates was further validated in porcine small intestinal epithelial cells (IPEC-J2) using both plate counting and Syto 9 staining methods. Interaction study suggested that the anti-adhesive activity of ovomucin hydrolysates was due to competitive binding to ETEC through K88ac fimbriae as decoy receptors. The peptide sequences of ovomucin glycopeptides play a role in binding to K88ac fimbriae while the glycan moieties are indispensable for this binding. The terminal β-linked galactose from ovomucin glycopeptides could be one of the binding sites for K88ac fimbriae. The anti-fouling property of ovomucin was studied by determining the adsorption of bovine serum albumin (BSA) on ovomucin-coated polystyrene surface. Ovomucin significantly inhibited BSA adsorption. To further confirm the anti-fouling property, directly surface force measurements between ovomucin and model proteins (BSA and ovomucin) were carried out using surface force apparatus (SFA). The SFA results suggested that pure repulsive forces were measured under both symmetric (ovomucin vs. ovomucin) and asymmetric configurations (BSA vs. ovomucin) at all tested pHs (2.0, 6.0 and 7.2) and ionic strengths (0.1, 10, and 150 mM NaCl) during approaching and separation. Atomic force microscope imaging, zeta potential and dynamic light scattering results suggested that the electrostatic and steric repulsions could be the main forces responsible for the anti-fouling property of ovomucin. This thesis demonstrated the potential applications of ovomucin as an ingredient for follow-up formula due to its high sialic acid content, an anti-adhesive agent against infection, and an anti-fouling surface.

• Subjects / Keywords

  • Anti-fouling property
  • Ovomucin
  • Hydrolysates
  • Anti-adhesive activity
  • Sialic acid

• Graduation date

  Spring 2017

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3G737G6T

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.