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Sugar beet pectin (SBP) and β-lactoglobulin (BLG) contain ferulic acid and tyrosine, respectively, potential substrates for laccase. Dispersions of BLG were treated with laccase and/or heat and SBP to assess potential for ferulic acid in SBP to influence laccase conjugation of BLG. Changes were investigated by size exclusion chromatography combined with multi angle laser light scattering (HPSEC-MALLS), refractive index (RI) and UV detector, particle size and ζ-potential analysis. Molecular weight (MW) of BLG decreased from 3.7 × 104 to 2.9 × 104 and root mean square (RMS) decreased from 41 to 36 after laccase treatment. The slope of a conformation plot increased from 0.35 to 0.72, indicating a change in shape in laccase treated BLG to more random coil. While laccase did not affect MW of BLG, MW of BLG increased after sequential heat and laccase treatment to 2.9 × 106 and 4.4 × 106, respectively. Free thiol (SH) increased by heat and laccase treatment of BLG; tyrosine in BLG increased only by heat. An increased MW and decreased ferulic acid in SBP was observed in the presence of BLG and laccase. The increase in MW was attributed to entrapment of BLG in SBP cross-linked matrix catalyzed by laccase. [ABSTRACT FROM AUTHOR]

Laccase, an oxidative enzyme, was used to catalyze the hetero and homo covalent conjugation between ferulic acid in sugar beet pectin (SBP) and tyrosine in heated β-lactoglobulin (H_BLG). The conjugation of SBP and H_BLG was confirmed by peak position using size exclusion chromatography, multi angle laser light scattering, refractive index, and UV detection. H_BLG, pre-treated with laccase, eluted at an earlier volume with greater UV280 absorbance than non-laccase treated dispersions. Tyrosine decreased in H_BLG that contained laccase treated SBP samples. Heat enhanced exposure of tyrosine in BLG and improved conjugation with SBP by laccase. H_BLG·SBP conjugates with laccase had improved solubility than laccase untreated dispersions at pH values near the isoelectric point of BLG. [ABSTRACT FROM AUTHOR]

Abstract: Laccase catalyzes intermolecular cross-links between ferulic acid of sugar beet pectin (SBP). Conjugation of SBP by laccase was confirmed by increased molecular weight, monitored by size exclusion chromatography, combined with multi-angle laser light scattering (SEC–MALLS), by reduced ferulic acid concentration detected at UV 325 nm, as well as by increased particle size. In addition, cross-linked SBP developed a more compact, branched structure as verified by a smaller root mean square (RMS) when molecular weight increased. Emulsions prepared with conjugated SBP had significantly smaller d 4,3 diameter and uniform droplet size, with more negative ζ-potential than non-treated SBP, during 30 days storage at 37 °C. The d 4,3 diameter was 5.3 μm and 3.8 μm for SBP and conjugated SBP, respectively. Covalently conjugated SBP has increased functionality and improved emulsion stability, most likely attributable to development of thick layer at the oil interface. [Copyright &y& Elsevier]