Functional changes in β-lactoglobulin by conjugation with carboxymethyl cellulose.

Abstract

β-lactoglobulin (BLG) and carboxymethylcellulose (CMC) were conjugated by using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC). The BLG-CMC conjugates with different CMC content and molecular weights were prepared. Confirmation of conjugation was carried out by SDS-PAGE. CD spectra revealed that the secondary structure of BLG had maintained in the conjugates. Fluorescence studies indicated that the conformation around Trp had not changed in the conjugates. Retinol-binding activity indicated that the retinol-binding site of BLG changed by the conjugation. Equilibrium constants (K_AS) of anti-BLG monoclonal antibodies (mAbs) to BLG after conjugating with CMC by competitive ELISA indicated that the structure around ¹⁵Val-²⁹Ile and ⁸Lys-¹⁹Trp maintained their native structure, and the structure around ¹²⁵Thr-¹³⁵Lys changed by conjugation. By conjugation with CMC, emulsifying property of BLG in the acidic pH region and in the presence of NaCl were much improved. Because acidic pH and salt are frequently used in food, the BLG-CMC conjugates are considered to be useful for food applications. Immunogenicity of BLG in BALB/c mice was reduced by this conjugation. In particular, there was a marked improvement in both emulsifying property and reduced immunogenicity in the BLG-high molecular weight (HMW) CMC conjugate. Therefore, conjugation with CMC is an effective way to improve BLG's function, and CMC with a high molecular weight is preferable.