Study of the thermal denaturation of selected proteins of whey and egg by low resolution NMR

The thermal denaturation of solutions of selected components of whey, albumen, and whole chicken albumen was studied during and after a heat treatment at constant temperatures by using low resolution nuclear magnetic resolution (LR-NMR) (on-line and off-line). Ovalbumin and conalbumin were isolated from albumen and β-lactoglobulin from milk, respectively. Pure proteins were studied separately and also in a 1+1 mixture of ovalbumin and β-lactoglobulin. Furthermore, albumen was heated. It was not only possible to record the integral change of molecular mobility due to denaturation processes, but also (a) to distinguish up to four phases of different mobility and to quantify the corresponding fractions and record their temporal evolution during the heat treatment, (b) to determine material-specific temperatures indicating structural changes including denaturation (denaturation temperatures based on data accessible by NMR), and (c) to differentiate, based on a combination of on-line and off-line LR-NMR, reversible and irreversible structural changes due to the thermal treatment as a function of both the process temperature and the duration of the heat treatment (more precisely: the process temperature/time history). Thus, the denaturation temperatures (based on NMR T2 experiments) of the single proteins, both dissolved alone and as a mixture. By comparison of the T2-relaxation times in solutions of single proteins (here: ovalbumin and β-lactoglobulin) and of the mixture of ovalbumin and β-lactoglobulin interactions between the proteins were observed. The advantage of NMR experiments is the possibility to perform on-line nondestructive in situ measurements, which is not possible by means of methods based on preparation.