The denaturation of α-lactalbumin and β-lactoglobulin in heated milk

Abstract

Summary The rates of denaturation by heat of α-lactalbumin and β-lactoglobulin in skim-milk were measured by an immunodiffusion method over a wide range of temperatures. Both reactions showed an unusual temperature dependence. The denaturation of α-lactalbumin is a first-order reaction; between 90 and 155 °C the kinetic constant k 1 in s −1 is given by the equation where T is the temperature in °K. The denaturation of β-actoglobulin in skim-milk is second order with respect to time, and the kinetic constant k 2 in 1g –1 s –1 is given by 2 equations, valid for different temperature ranges. Between 68 and 90 °C, Between 90 and 135 °C Results obtained by the immunodiffusion method agreed well with those found by salt fractionation of the milk proteins. The denaturation rates decreased when a specific reagent for sulphydryl groups was added, suggesting that such groups are involved in the denaturation of both proteins.