Innovative FT-IR imaging of protein film secondary structure before and after heat treatment.

Changes in the secondary structure of globular protein occur during thermal processing. An infrared reflecting mirrored optical substrate that is unaffected by heat allows recording infrared spectra of protein films in a reflection absorption mode on the stage of an FT-IR microspectrometer. Hydrated films of myoglobin protein cast from solution on the mirrored substrate are interrogated before and after thermal denaturation to allow a direct comparison. Focal plane array imaging of 280 protein films allowed selection of the same area in the image from which to extract spectra. After treatment, 110 of 140 spectra from multiple films showed a dramatic shift from the alpha-helix form (1650 +/- 5 cm(-1)) to aggregated forms on either side of the original band. Seventy maxima were near 1625 cm(-1), and 40 shifted in the direction of 1670 cm(-1). The method developed was applied to films cast from two other commercial animal and plant protein sources.