Cross-Linking Proteins by Laccase-Catalyzed Oxidation: Importance Relative to Other Modifications

Abstract

Laccase-catalyzed oxidation was able to induce intermolecular cross-links in beta-lactoglobulin, and ferulic acid-mediated laccase-catalyzed oxidation was able to induce intermolecular cross-links in alpha-casein, whereas transglutaminase cross-linked only alpha-casein. In addition, different patterns of laccase-induced oxidative modifications were detected, including dityrosine formation, formation of fluorescent tryptophan oxidation products, and carbonyls derived from histidine, tryptophan, and methionine. Laccase-catalyzed oxidation as well as transglutaminase induced only minor changes in surface tension of the proteins, and the changes could not be correlated to protein cross-linking. The presence of ferulic acid was found to influence the effect of laccase, allowing laccase to form irreducible intermolecular cross-links in beta-lactoglobulin and resulting in proteins exercising higher surface tensions due to cross-linking as well as other oxidative modifications. The outcome of using ferulic acid-mediated laccase-catalyzed oxidation to modify the functional properties of proteinaceous food components or other biosystems is expected to be highly dependent on the protein composition, resulting in different changes of the functional properties.

Cross-linking oppositely charged oil-in-water emulsions to enhance heteroaggregate stability

“…Therefore, the concentration of phenolic compounds might have been too low for substantial laccaseinduced cross-linking. In agreement, Steffensen et al [28] found that higher dosages of phenolic compounds, such as ferulic acid, enhanced the effect of laccase catalyzed crosslinking of proteins. Supporting the above described hypothesis, the low glutaraldehyde concentrations of 0.5 µM resulted in only slightly larger heteroaggregates as compared to those of the untreated ones (Figure 3).…”

Size Separation Techniques for the Characterisation of Cross-Linked Casein: A Review of Methods and Their Applications

“…Using SDS-PAGE, the cross-linking potential of laccase preparations from different microbial origins [98] as well as the suitability of different reaction-mediating additives [99] were evaluated for application in milk gels. The necessity of mediators such as ferulic acid to facilitate casein cross-linking by laccase was also reported in other studies [85,100]. Dinnella et al [101] showed that casein polymerisation by TGase is limited in the presence of N-carbobenzoxy-glutaminyl-glycine (Z-Gln-Gly) because of the enzyme's higher affinity for the low molecular weight γ-glutamyl donor.…”

“…Similar results were reported by Liu & Damodoran [82], who also showed that dimers, trimers, and tetramers of β-casein migrate like globular proteins with molar mass of~72,~110, and~150 kg/mol, respectively, manifesting that molar mass markers are not suitable for correct assessment of casein polymers. In contrast to that, molar mass evaluation by SDS-PAGE worked well for cross-linked whey proteins [83][84][85][86][87]. Different polymeric fractions of casein homopolymers may be visually distinguishable to some extent (Figure 7b; see also [82,88]).…”

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

“…Ferulic acid is a phenolic compound with low toxicity widely used in food and cosmetic industries (Ou & Kwok, 2004). The use of ferulic acid as mediator has been reported to enhance the effects of laccasecatalyzed oxidation of proteins by increasing the accessibility of the reactive amino acids, such as tyrosine and tryptophan, thus improving cross-linking process (Cura et al, 2009;Mattinen et al, 2005;Steffensen, Andersen, Degn, & Nielsen, 2008). Ferulic acid acts as bridging agent in the cross-linking of α-casein, enhancing the laccase-mediated cross-link of the protein (Selinheimo, Lampila, Mattinen, & Buchert, 2008).…”