Determination of heat-induced changes in the protein secondary structure of reconstituted livetins (water-soluble proteins from hen's egg yolk) by FTIR

This study characterized the impact of technological treatments on the protein secondary structure of a newly developed egg yolk livetin formulation and its components α-livetin, which is identical with chicken serum albumin, and γ-livetin, the bioactive antibody immunoglobulin Y. Fourier transform infrared (FTIR) spectroscopy at 25 °C revealed that the largest proportion of conformal elements comprised intramolecular (native) β-sheets (60-80%) in γ-livetin, and α-helices/random coils (60.59%) in α-livetin. In reconstituted freeze-dried livetins, the main protein conformations were also intramolecular (native) β-sheets (55.08%) and α-helices/random coils (30.51%), but upon heating from 25 to 95 °C, the former decreased sigmoidally at the onset-of-denaturation temperature (TOD (FTIR)) of 69.5 °C, concomitant with a sigmoidal increase in intermolecular (denatured) β-sheets at a TOD (FTIR) of 72.4 °C and a sigmoidal decrease in IgY activity at TOD (ELISA) of 67.5 °C. Reconstituted spray-dried livetins showed less native β-sheets and significantly lower TOD (FTIR) values than freeze-dried livetins.