Thermal Aggregation of β-Lactoglobulin: Effect of pH, Ionic Environment, and Thiol Reagent

Abstract

Heat-induced β-lactoglobulin (1.2 mg/ml) aggregation in NaCl, CaCl2, and thiol-blocking agent (N-ethylmaleimide) solutions was determined by measuring dynamic turbidity changes at temperatures ranging from 25 to 96°C. β-Lactoglobulin in distilled water exhibited a single transition (≥76°C) in protein-protein interaction (aggregation). An increase in pH from 5.50 to 6.50 suppressed the transition, whereas addition of NaCl (.02 to 1.0 M) and CaCl2 (.005 to .2 M) promoted the transition. N-Ethylmaleimide (4.0 to 10.0 mM) decreased the transition temperature and, in the absence of salts, induced a second transition. However, the combination of N-ethylmaleimide and NaCl or CaCl2 produced a single, large transition peak. Results indicate that β-lactoglobulin aggregation is most sensitive to low pH, greatly depends on the type and concentration of specific salts, and involves electrostatic and possibly hydrophobic forces and sulfhydryl reactions. © 1993, American Dairy Science Association. All rights reserved.