Rheological properties of sodium caprate-induced β-lactoglobulin gel and changes in secondary structure during gelation

In this study, we found that transparent gels of beta-lactoglobulin (beta-LG) were formed by adding different concentrations of sodium caprate to protein solutions at ambient temperature. We investigated changes in the dynamic viscoelasticity of the mixture with time at 25degreesC and found that more than 12% beta-LG induced the formation of a viscoelastic gel with a suitable amount of sodium caprate (for example, 12%, beta-LG and 3.6%, sodium caprate). Furthermore, we analyzed the changes in the secondary structure of proteins during the gelation step by FTIR spectroscopy. Dissociation of the beta-LG dimer was first observed just after mixing with sodium caprate. Furthermore, in the beta-LG protein in which the original contents were predominantly sheets, intermolecular beta-sheets attributable to aggregation increased with a decrease in the content of intramolecular sheets. Sodium caprate-induced gel was heated at 80degreesC for 30 min after the gel was formed, and a large increase in the intermolecular beta-sheet bands was observed by heat treatment. These results suggest that the formation of sodium caprate-induced gels of beta-LG was accompanied by less marked changes in the protein conformation than those in heat-induced gels.