title: Heat-induced aggregation of beta-lactoglobulin as a function of pH.
abstract: The effect of pH in the range 6.0-8.0 on the denaturation and aggregation of beta-lactoglobulin (beta-lg) was investigated. Results were interpreted in terms of the reaction scheme for the denaturation and aggregation of beta-lg proposed by Roefs and De Kruif (Eur. J. Biochem. 1994, 226, 883-889). The rate of conversion of native beta-lg increased strongly at higher pH values, whereas the molecular mass of the aggregates decreased strongly. In the pH range 6.4-8.0 aggregates were formed mainly by intermolecular disulfide bonds, but even at pH 6.0, thiol/disulfide exchange reactions were involved, although to a lesser extent. The time course of the exposure of the thiol group in native beta-lg upon heating and the subsequent disappearance of this group through the formation of disulfide-linked aggregates was investigated by reaction with 5,5'-dithiobis(2-nitrobenzoic acid) and varied strongly with pH. These observations could be used, in combination with the reaction steps of the reaction scheme, to describe qualitatively the strongly pH-dependent isothermal calorimetry curves, measured at 65 degrees C.
authors.affiliation: NIZO Food Research, Ede, The Netherlands.
authors.forename: M A
authors.initials: MA
authors.lastname: Hoffmann
authors.forename: P J
authors.initials: PJ
authors.lastname: van Mil
mesh_terms: D000818:Animals; D002151:Calorimetry; D002417:Cattle; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D007782:Lactoglobulins / Q000737:chemistry*; D011489:Protein Denaturation; D013816:Thermodynamics
chemical_list: D007782:Lactoglobulins