Enhancing the gelation of β-lactoglobulin

Abstract

The gelation characteristics of bovine beta-lactoglobulin A (BLGA) have been enhanced by the selective introduction of cysteine substitutions to increase the free thiol content of the protein. A recombinant version of bovine beta-lactoglobulin A (rBLG) has been modified by creating R40C (substitution of arginine at position 40 with cysteine), F82C (substitution of phenylalanine at position 82 with cysteine), and the double R40C/F82C variants. As expected, the number of free thiols increased correspondingly, suggesting that additional disulfide linkages are not formed. The strength of gels formed by heating at 70-90-degrees-C was measured using a microscale penetration test. F82C and R40C/F82C displayed a gel strength equivalent to that of wild-type BLGA at a much lower concentration as compared to wild-type BLGA. R40C could not be brought to a sufficient concentration (>5%) without the formation of insoluble aggregates. Increasing the free thiol content also enhanced the ability of rBLG to form high molecular weight aggregates as observed during the heating of milk. An unexpected result was that the introduction of a free thiol also increased the ability of these rBLG variants to be cleaved by chymosin. Similarly, these variants were more susceptible to acid precipitation. These latter observations may be important for improving the performance of BLGA during the renneting process.