Cross-linking proteins by laccase: Effects on the droplet size and rheology of emulsions stabilized by sodium caseinate

Abstract

The aim of this work was to evaluate the influence of laccase and ferulic acid on the characteristics of oil-in-water emulsions stabilized by sodium caseinate at different pH (3, 5 and 7). Emulsions were prepared by high pressure homogenization of soybean oil with sodium caseinate solution containing varied concentrations of laccase (0, 1 and 5mg/mL) and ferulic acid (5 and 10mM). Laccase treatment and pH exerted a strong influence on the properties with a consequent effect on stability, structure and rheology of emulsions stabilized by Na-caseinate. At pH7, O/W emulsions were kinetically stable due to the negative protein charge which enabled electrostatic repulsion between oil droplets resulting in an emulsion with small droplet size, low viscosity, pseudoplasticity and viscoelastic properties. The laccase treatment led to emulsions showing shear-thinning behavior as a result of a more structured system. O/W emulsions at pH5 and 3 showed phase separation due to the proximity to protein pI, but the laccase treatment improved their stability of emulsions especially at pH3. At pH3, the addition of ferulic acid and laccase produced emulsions with larger droplet size but with narrower droplet size distribution, increased viscosity, pseudoplasticity and viscoelastic properties (gel-like behavior). Comparing laccase treatments, the combined addition of laccase and ferulic acid generally produced emulsions with lower stability (pH5), larger droplet size (pH3, 5 and 7) and higher pseudoplasticity (pH5 and 7) than emulsion with only ferulic acid. The results suggested that the cross-linking of proteins by laccase and ferulic acid improved protein emulsifying properties by changing functional mechanisms of the protein on emulsion structure and rheology, showing that sodium caseinate can be successfully used in acid products when treated with laccase.

Covalent modification of soy protein isolate by (−)‐epigallocatechin‐3‐gallate: effects on structural and emulsifying properties

“…This phenomenon has also been observed previously in O/W emulsions stabilized with crosslinked egg white protein and sodium caseinate . However, the rheological characterization of emulsion was influenced by the crosslinking of protein stabilizer, which could form a network and increase the viscosity of the continuous phase in emulsion . According to Stokes's law, the creaming rate is inversely proportional to the viscosity of the continuous phase.…”

“…39 However, the rheological characterization of emulsion was influenced by the crosslinking of protein stabilizer, which could form a network and increase the viscosity of the continuous phase in emulsion. 40,41 According to Stokes's law, the creaming rate is inversely proportional to the viscosity of the continuous phase. Thus, an additional interpretation of the better creaming stability may be the increased viscosity of emulsions of EGCG-modified SPI, which delays upward migration of oil droplets.…”

Polymerization of Horseradish Peroxidase by a Laccase‐Catalyzed Tyrosine Coupling Reaction

“…To the best of our knowledge, until now, researchers have used mediators to assist laccase in the oxidation reaction of phenolic compounds and to initiate the protein polymerization. Most of the mediators are phenolic acids and their derivatives including ferulic acid, p‐ coumaric acid, caffeic acid, vanillic acid, and hydrolyzed oat spelt xylan (hOSX) . The mediators are small molecules and possess high reactivity against laccase to form radicals.…”

Laccase‐catalyzed, Phytochemical‐mediated Protein Crosslinking Conjugates

“…As for the enzyme sources, most of the reported studies focused on using laccases originated from fungi and mushrooms. Among these reviewed studies, half of them involved using laccases from Trametes hirsuta and Trametes versicolor [28,[30][31][32][33]36].…”