Lactalbumin thermal denaturation

Thermal denaturation, recovery of precipitated protein by filtration/ centrifugation and spray-drying, to yield lactalbumin which has very low solubility and limited functionality. 

Thermal denaturation is a traditional method for the recovery of proteins from whey as lactalbumin coagulation is optimal at pH 6 and about 90°C for 10 min (Chapter 4). 

Bernal, V. and Jelen, P. 1984. Effect of calcium binding on thermal denaturation of bovine a-lactalbumin. J. Dairy Sci. 67, 2452-2454. 

Although less frequently discussed, heat processes often influence the textures and chemistries of the intermediate and end products, and thermal treatments are not without consequences on milk proteins that are denatured. Denaturation of proteins occurs under precise conditions of pH, temperature and ionic strength leading to their unfolding. Denaturation is significantly slower when proteins are near their isoelectric point. Only (3-lactoglobulin is irreversibly denatured at pH 7 and 70°C a-lactalbumin is denatured at pH 6.7 and 65°C. Aggregation of these proteins, besides hydrophobic... 

Wang, Q., Tolkach, A., and Kulozik, U. (2006). Quantitative assessment of thermal denaturation of bovine a-lactalbumin by low-intensity ultrasound in comparison to HPLC and DSC. J. Agric. FoodChem. 54, 6501-6506. 

Musci and Berliner (1985b) concluded that apo-a-lactalbumin is more efficient as the modifier protein in the lactose synthase system than is the Ca(II)-bound form. They found that Vniax for the apo form shows a 3.5-fold increase over that for the Ca(II)-bound form, but there is no difference in (app.) between the two forms. They also confirmed that calcium stabilizes the protein against thermal denaturation (see Section IX,E), but that zinc is crucial in shifting the protein toward the apo-like form that is optimally active in lactose synthase. Their model is summarized schematically in Fig. 9. 

D. Thermal Modifications of Structure and Co-denaturation of a-lactalbumin and p-lactoglobulin... 

D. THERMAL MODIFICATIONS OF STRUCTURE AND CO-DENATURATION OF a-LACTALBUMIN AND fULACTOGLOBULIN... 

Bertrand-Harb, C., Baday, A., Dalgalarrondo, M., Chobert, J.-M., and Haertle, T. 2002. Thermal modifications of structure and co-denaturation of a-lactalbumin and (3-lactoglobulin induce changes of solubility and susceptibility to proteases. Nahrung 46, 283 —289. 

Tolkach, A., and Kulozik, U. (2005). Optimization of thermal pretreatment conditions for the separation of native a-lactalbumin from whey protein concentrates by means of selective denaturation of p-lactoglobulin. J. Food Set., 70(9), 557-566. 

Pfeil (1981) concluded that a-lactalbumin is less stable than lysozyme, with a lower thermal transition temperature, lower denaturational enthalpy, lower heat capacity change, and lower Gibbs free-energy change. 

It should be noted that ultrasonic technology is a non-thermal process and hence very little changes to the physical and functional properties of dairy system is observed due to sonication. In most studies, the processing time required is a few seconds to less than a minute. In order to evaluate the effect of sonication on the constituents of milk, Chandrapala et al. [85] and Shanmugam et al. [86] carried out extensive research in recent years. Their studies have shown that sonication of a dairy system causes very little changes to the physical properties of whey proteins. They observed reversible changes to partial denaturation of whey proteins. In order to see the effect, the constituents of whey proteins, namely, pure- and 3 1 mixtures of p-Lactoglobulin (P-LG) and a-Lactalbumin (a-LA)... 

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