Whey protein denaturation in heated milk and cheese whey

Abstract

Quantitative polyacrylamide gel electrophoresis has been used to measure residual native whey proteins remaining after heat treatment of skim-milk and cheese whey in a kinetic study. The denaturation of a-lactalbumin (a-la) appeared to be first order, but was probably a second-order reaction displaying pseudo firstorder kinetics. The denaturation of both yff-lactoglobulin A and B (/MgA and /MgB) followed second-order kinetics while that of serum albumin was more complex, and could equally well be described as first or second order. Equations are given relating log k x (in s-1 ) to temperature for a-la denaturation in skim-milk between 70 and 95 °C and between 100 and 150 °C. Similarly, equations relating log k 2 (in lg-1^-1 ) to temperature are given for /MgA in skim-milk between 100 and 150 °C, and for yff-lgB between 95 and 150 °C. The relative heat stability of /MgA and /MgB was found to vary.Below 95 °C /MgA appeared slightly more thermostable than /MgB in skim-milk, and the same was observed in cheese whey below 100 °C. Above these temperatures yff-lgB appeared more stable than /MgA. Denaturation of /MgB was only slightly more rapid in skim-milk than in whey at temperatures below 95 °C, but was significantly slower at higher temperatures.The recovery of residual protein from cheese whey is important to the dairy industry, and the denaturation of these whey proteins is therefore of considerable interest. However, the many studies which have been reported are often not directly comparable because of the variation in experimental technique and in the means used to express results. Kinetic data on rates of denaturation are rarely available, and then are not always in agreement. Lyster (1970), using immunochemical techniques, has measured the rates of denaturation of a-lactalbumin (a-la) and /Mactoglobulin (/?-lg) in heated milk, and found a-la to follow first-order kinetics, while /Mg followed second-order kinetics. Other workers have reported the denaturation of y#-lg as first order (Gough & Jenness, 1962). A rapid accurate measure of individual native whey proteins in complex mixtures is possible using polyacrylamide gel electrophoresis (PAGE) (Hillier, 1976;Darling & Butcher, 1976). This technique has been used for a comprehensive study of the kinetics of denaturation of the major proteins in milk and cheese whey over a wide range of temperatures.

Kinetics of heat-induced association of β-lactoglobulin and α-lactalbumin with milk fat globule membrane in whole milk

“…(i) denaturation of individual protein of the MFGM, b-lg and a-la (Appell, Keenan, & Low, 1982;Hillier & Lyster, 1979); (ii) association of individual polypeptides of MFGM (Appell et al, 1982;Ye et al, 2002) and selfaggregation of b-lg and a-la; (iii) association of individual protein or associated protein complexes of the MFGM with individual b-lg and a-la or with aggregates of b-lg and a-la; consequently PAS 7 or the complex of b-lg and PAS 7 possibly leaving the MFGM (Dalgleish & Banks, 1991;Houlihan et al, 1992;Ye, Singh, Taylor, & Anema, 2003). Table 2 Change in enthalpy of activation, DH # ; free energy of activation, DG # ; and entropy of activation, DS # ; between 65 C and 95 C for association of b-lg and a-la with the MFGM proteins in heated early-, mid-and late-season milks According to the principle that the slowest process is the rate-determining step, regardless of how many processes are involved, it is possible to deduce this rate determining step from the kinetic and thermodynamic results of this study.…”

Controlling milk protein interactions to enhance the reconstitution properties of whole milk powders – A minireview

“…The denaturation of α-lactalbumin appears to follow a pseudo-first-order reaction, but the order of reaction for β-lactoglobulin has not been elucidated. Dannenberg and Kessler [7] suggest that a reaction order of 1.5 is best to fit the rate of denaturation, but other workers favour either a first-order [8] or a second-order [11] reaction. Despite these differences, there is general agreement that the denaturation reaction shows a non-linear Arrhenius plot, with a marked change in temperature dependence at about 80−90°C for both α-lactalbumin and β-lactoglobulin.…”

Coagulation présure du lait et des rétentats d'ultrafiltration. Effets de divers traitements thermiques

“…Un traitement thermique de 70 oC pendant 1 min entraîne une dénaturation de l'ordre de 5% alors que le maintien du lait à 90 oC -1 min conduit à une insolubilisation de 42% des protéines solubles. Ces valeurs sont en bon accord avec celles observées par Harland et al (1952), Larson et Rolleri (1955), Hillier et Lyster (1979), Dannenberg et Kessler (1988).…”