FTIR 2D correlation spectroscopy of α1 and α2 fractions of an alkali-pretreated gelatin

An alkali-pretreated gelatin (pI ~ 4.9) was fractionated by means of alcohol coacervation and semi-preparative gel chromatography. The thermal responses of the isolated α fractions, the coacervate and the total gelatin were investigated by 2D-correlation FTIR spectroscopy in the amide I band region (1600–1700 cm− 1). The gelation temperature was the same for all examined samples (24.5 °C) while the melting temperature of the α2 fraction was lower (30 °C) than that of the other samples (32.5 °C). The 2D COS plots indicate that on cooling (gelation) the core sequence of conformational changes is the same for all samples. On heating, however, the α2 fraction deviates from the α1-containing samples and shows an earlier disappearance of the triple helix signal in the event sequence. The lower melting temperature (less thermostable gelatin gel) of the α2 fraction thus results from a different conformational cascade of the α2 chains upon melting. In all samples the initial conformational changes take place in the β-turns, providing further evidence for the models proposed previously.

Research Highlights
► An alkali-pretreated gelatin was fractionated.
► The melting temperature of the α2 fraction was lower than for the other samples.
► The melting temperature of the α2 fraction was lower than for the other samples.
► On heating the α2 fraction deviates from the α1-containing samples.
► In all samples the initial conformational changes take place in the β-turns.