Reaction Kinetics of Thermal Denaturation of Whey Proteins in Heated Reconstituted Whole Milk

Abstract

Reconstituted whole milk was heated using pilot-scale heating equipment. Kinetic and thermodynamic parameters for the irreversible denaturation of β-lactoglobulins A and B and R-lactalbumin were determined. R-Lactalbumin denaturation was first order, whereas both β-lactoglobulin variants had a reaction order of 1.5. Arrhenius plots for all three proteins showed an abrupt change in temperature dependence. In the low-temperature range, the thermodynamic parameters were ascribed to typical denaturation processes in which the unfolding of the protein tertiary structure is the rate-determining step. At higher temperatures, these parameters were in the range expected for typical condensation reactions, suggesting that aggregation processes may be rate-determining in this temperature range. The rate constants for β-lactoglobulin denaturation were independent of the initial protein concentration at all temperatures. For R-lactalbumin at temperatures below 85 °C the rate constants may have been dependent on the initial R-lactalbumin concentration as higher rate constants were observed with decreasing protein concentrations.

Influence of moderate electric fields on gelation of whey protein isolate

“…As expected, concentration of soluble native whey proteins decreased with an increase in holding time, and the degrees of denaturation were higher than 90% after 5 min of heating at 85 o C. The denaturation levels observed were slightly higher (10-15%) than those observed elsewhere (Anema & Li, 2003;Dannenberg & Kessler, 1988;Oldfield, Singh, Taylor, & Pearce, 1998). This can be explained by the fact that, during processing to obtain WPI powder, partial unfolding of the major whey proteins may occur that results in a more rapid denaturation on the subsequent heating treatments (Anema & McKenna, 1996). Moreover, these authors studied the disappearance of native whey proteins in skim raw milk fractions, and suggested that some of the constituents may have influenced the rate of denaturation.…”

Functional implications of structural differences between variants A and B of bovine β‐lactoglobulin

“…There is a vast and somewhat confusing literature on the different chemical and physical properties of BLG, such as chemical reactivity of the free cysteine at position 121, thermal denaturation, Dannenberg & Kessler, 1988;Anema & McKenna, 1996;Hill et al, 1996!, and induces more readily the coagulation of milk at 140 8C~Rose, 1962; Feagan et al, 1972;McLean et al, 1987;van den Berg et al, 1992;Robitaille, 1995;Hill et al, 1996!-all undesirable properties for various heat treatments involved in standard milk processing~Hill et al, 1996!. Variant C is noticeably more stable than variant B to both thermal~Manderson et al, 1995thermal~Manderson et al, , 1998Hill et al, 1996!…”

Potentiality of spectroscopic methods for the characterisation of dairy products. I. Front-face fluorescence study of raw, heated and homogenised milks

“…In addition, it is weil known that the temperature of~-Iactoglobulin denaturation depends on the protein environment. Anema and McKenna (1996) showed that -lactoglobulin in reconstituted whole milk was not or slightly denatured at 70 and 75°C. On the contrary, it was reported that oe-lactalbumin is partly denatured at 70 "C (Anema and McKenna, 1996).…”

“…Anema and McKenna (1996) showed that -lactoglobulin in reconstituted whole milk was not or slightly denatured at 70 and 75°C. On the contrary, it was reported that oe-lactalbumin is partly denatured at 70 "C (Anema and McKenna, 1996). Whatever the conditions studied, electrophoresis data showed, however, that~-lactoglobulin bound weakly to the fat globule.…”