Title: FT-HATR DETERMINATION OF PROTEIN SECONDARY STRUCTURES ASSOCIATED WITH DOUGH RHEOLOGY Authors
Submitted to: UJNR Food & Agricultural Panel Proceedings
Publication Type: Proceedings
Publication Acceptance Date: August 24, 2005
Publication Date: October 29, 2005
Citation: Seabourn, B.W., Chung, O.K. Ft-hatr determination of protein secondary structures associated with dough rheology. In: Proceedings of the 34th UJNR Cooperative Program in Natural Resources Food and Agriculture Panel, October 23-29, Tsukuba, Japan. Interpretive Summary: More objective methods for measuring the development of flour/water (dough) systems, preferably methods based on the chemical characteristics of dough component interaction(s), have long been desired by cereal chemists. The mixograph and farinograph have traditionally been used to determine the rheological characteristics of dough systems for many years, but these devices are subjective and labor-intensive methods. They also do not provide any information on the fundamental chemistry at work in the dough, particularly the changing characteristics of the flour protein that are believed to occur as it is mixed with water. The use of infrared spectroscopy in biological applications, particularly in the characterization of proteins, has seen an unprecedented increase in recent years. The infrared signatures of proteins are quite unique, and provide a means for chemists to "fingerprint" protein composition and structure. The purpose of this study was to use infrared spectroscopy to study flour as it mixed with water, identify the changes in protein structure that are assumed to occur during mechanical mixing, and determine how these changes relate to the rheological properties of the dough system. It was found that certain well-characterized protein structures increase in amount during mixing, and the rate at which these structures increase have a direct relationship to the rheological characteristics of the dough system.
Technical Abstract: Cereal chemists have long desired more objective methods for measuring the development of flour/water (dough) systems, preferably methods based on the chemical characteristics of dough component interaction(s). The mixograph and farinograph have traditionally been used to determine the rheological characteristics of dough systems by the wheat milling and baking industry for many years. However, these devices utilize subjective, labor-intensive methods. In addition, they do not provide any information on the fundamental chemistry at work in the dough, particularly the changing characteristics of the flour protein that are believed to occur as it is mixed with water. In this study, an infrared spectroscopic method was developed to examine changes in the secondary structure of gluten proteins in a flour-water dough system during mixing. Fourier transform horizontal attenuated total reflectance (FT-HATR) mid-infrared spectra of mixed dough revealed changes in four bands in the amide III region typically associated with secondary structure of proteins: 1317 (alpha-helix), 1285 (beta-turn), 1265 (random coil), and 1242 cm-1 (beta-sheet). The largest band, which also showed the greatest change in second derivative band area (SDBA) during mixing (increasing over time), 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 (minimum mobility) corresponding to the proper development of the dough as determined by the mixograph. Increases in alpha-helical, beta-turn, and beta-sheet secondary structures during mixing suggest that the dough proteins assume a more ordered conformation, and the decrease of SDBA at 1265 cm-1 suggests this occurs at the expense of the random coil structural components. These results demonstrate that it is possible, using infrared spectroscopic techniques, to relate the rheological behavior of developing dough directly to changes in the structure of the gluten protein system.