Study on β-lactoglobulin glycosylation with dextran: effect on solubility and heat stability

In this paper, the characteristics of purified conjugates formed between β-lactoglobulin (β-lg) and a high molecular weight dextran under different dry heating conditions were investigated. SDS-PAGE analyses under non-reducing and reducing conditions showed that glycation of β-lg led to the formation of high molecular weight complexes and induced polymerization of the protein by disulfide bonds. The fluorescence emission spectra did not show changes in λmax, which was indicative of a similar conformation around Trp residues. The conjugate formed at 60 °C, 0.44 aw and 2:1 weight ratio of dextran to β-lg (conjugate 1) exhibited a fluorescence intensity very similar to that of the native protein and was selected to study the influence of glycosylation on the solubility and heat-stability properties. Solubility of conjugate 1 was higher than that of the dry-heated β-lg in the pH range from 3 to 9 and, particularly, around the isoelectric point of the protein. As compared to the native protein, the solubility of the conjugate decreased at pH 4. The glycated β-lg presented lower stability to heating at pH 7.0 than native β-lg, but its thermal stability was higher at pH 5.0 at temperatures above 85 °C.