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

Abstract

SummaryThe 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 k1 in s−1 is given by the equationwhere 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 k2 in 1g–1 s–1 is given by 2 equations, valid for different temperature ranges. Between 68 and 90 °C,Between 90 and 135 °CResults 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.