Determination of Secondary Structural Changes in Gluten Proteins during Mixing Using Fourier Transform Horizontal Attenuated Total Reflectance Spectroscopy

Fourier transform horizontal attenuated total reflectance (FT-HATR) was used to examine changes in the secondary structure of gluten proteins in a flour−water dough system during mixing. Midinfrared spectra of mixed dough revealed changes in four bands in the amide III region associated with secondary structure in proteins: 1317 (α-helix), 1285 (β-turn), 1265 (random coil), and 1242 cm−1 (β-sheet). The largest band, which also showed the greatest change in second derivative band area (SDBA) during mixing, was located at 1242 cm−1. The bands at 1317 and 1285 cm−1 also showed an increase in SDBA over time. Conversely, the band at 1265 cm−1 showed a corresponding decrease over time as the doughs were mixed. All bands reached an optimum corresponding to the minimum mobility of the dough as determined by the mixograph. Increases in α-helix, β-turn, and β-sheet secondary structures during mixing suggest that the dough proteins assume a more ordered conformation. These results demonstrate that it is possible, using infrared spectroscopic techniques, to relate the rheological behavior of developing dough in a mixograph directly to changes in the structure of the gluten protein system.