An investigation of the effect of microwave treatment on the structure and unfolding pathways of β-lactoglobulin using FTIR spectroscopy with the application of two-dimensional correlation spectroscopy (2D-COS)

Microwave treatment of β-lactoglobulin (β-Lg) in D2O solution under various conditions was monitored by Fourier transform mid infrared (mid-FTIR) spectroscopy. At sub-ambient temperatures, no microwave-induced changes in the conformation of the protein were detected. Microwave heating of the β-Lg solutions to temperatures in the range of 40–60 °C resulted in a marked increase in the rate of hydrogen–deuterium (H–D) exchange as compared to conventional heating at the same temperature. At heating temperatures in the range of 70–90 °C, the microwave-heated solutions exhibited more extensive protein aggregation than conventionally heated solutions. Application of two-dimensional (2D) correlation analysis to the Fourier self-deconvolved FTIR spectra recorded as a function of number of cycles of microwave or conventional heating revealed that the unfolding pathway of β-Lg was different in these two temperature ranges (40–60 °C versus 70–90 °C) but was similar in both microwave – treated and conventionally heated samples. Nevertheless, within the temperature range of 70–90 °C microwave treatment accelerated the unfolding of β-lactoglobulin.

► FTIR spectra of microwave treated and conventionally heated β-lactoglobulin were compared. ► Microwave treatment at sub-ambient temperature did not alter the protein's conformation. ► Disruption of tertiary structure at 40–60 °C was enhanced by microwave treatment. ► Protein aggregation was more extensive during microwave treatment than during conventional heating. ► Unfolding pathways, as determined by 2D COS analysis, were similar during microwave treatment and conventional heating.