Heat-induced denaturation/aggregation of β-lactoglobulin A and B:: kinetics of the first intermediates formed

The heat-induced denaturation/aggregation of bovine beta-lactoglobulin (beta-1g) A and B, dispersed at pH 6.6 in various salt conditions (NaCl and CaCl2), was studied at 85degreesC by High-performance Gel Permeation Chromatography. Results confirmed earlier studies Croguennec, Bouhallab, Molle, O'Kennedy, & Mehra (Biochem. Biophys. Res. Commun. 301 (2003) 465) that in the early stages of the denaturation/aggregation process, native beta-1g molecules unfolded to native thiol-exposed monomers (Mcys121) and non-native thiol-exposed monomers (Mcys119). Whereas Mcys121 monomers formed intermediate oligomers (dimer, trimer, tetramer) which rapidly combined to larger aggregates in the presence of CaCl2 and to a lesser extend in the presence of NaCl, Mcys119 monomers trapped beta-1g molecules in a conformation that slow down its aggregating behavior at pH 6.6. Results also highlighted that the quantity of Mcys119 formed on heating was related to the rate of condensation of Mcys121 into intermediate oligomers and/or aggregates independent of the salt conditions. (C) 2003 Elsevier Ltd. All rights reserved.