Study On The Gelling And Thickening Properties Of β-lactoglobulin Fibrils

β-Lactoglobulin(BLG) is the main component of whey proteins, which has been widely used in the food industry as gelling and emulsifying agents. Protein fibril is formed by the self-assembling of proteins under certain conditions, and it is regarded as a novel functional food ingredient. This project investigated the formation and the basic physicochemical properties of BLG fibrils. The gelation behaviors of BLG and BLG fibril induced by TGase were compared, and the influence of dithiothreitol(DTT) on the gelation behaviors was examined. Furthermore, the interaction between BLG fibril and λ-carrageenan and its impact on the rheological properties of the mixtures were investigated. Main conclusions are as follows:1. Stable fibrils were formed when 2.0 %(w/w) BLG was heated for 10 hours under 80 oC at pH 2.0. The conversion rate was measured to be 69%. Zeta potential measurement demonstrated an increased surface charge after fibril formation. The fibrils were stable under pH 2.0, which however tended to aggregate at pH 7.0, resulting in a decrease in contour length and an increase in fibril diameter. Amino acid composition was found not to change significantly before and after fibril formation. Gelation occurred when BLG fibrils dispersion(3.0% w/w) was heated above 60 oC, and it was found that disulfide bond and hydrogen bond were the driving force for the gelation.2. As for the transglutaminase(TGase)-induced gelation, DTT was required in the case of BLG gels, while DTT was not necessary for the gelation of BLG fibrils. This indicated that the protein was fully unfolded upon the formation of fibrils, resulted in more crosslinking sites available for TGase.3. In comparison with BLG, the TGase-induced gelation of BLG fibrils proceeded more rapidly, resulting in a higher gel storage modulus. The critical gelation concentration decreased markedly from 7.18(w/w) for BLG to 1.16%(w/w) for fibrils. However, the linear viscoelastic region of fibril gels was narrower than that of BLG gels, indicating a more brittle nature of fibril gel.4. At the same concentration of λ-carrageenan, the viscosity of the mixture of BLG fibril and λ-carrageenan was 10 times larger than that of BLG and λ-carrageenan. Compared to BLG, the fibrils exhibited a stronger interaction with λ-carrageenan and a higher degree of intermolecular entanglement, leading to a more pronounced effect of thickening. Addition of NaCl suppressed the complex coacervation of BLG fibril and λ-carrageenan, increased the homogeneity of the mixture, and thus promoted the intermolecular entanglement. Addition of SDS however was found to decrease the hydrophobic interaction of BLG fibril and λ-carrageenan. The results together suggested that electrostatic attraction, hydrophobic interaction, and intermolecular entanglement were the determining factors for the interaction of BLG fibril and λ-carrageenan, influencing the thickening effect.