FTIR investigation of the secondary structure of type I collagen: New insight into the amide III band

This work presents a thorough study on the Amide III band in fibrous proteins using Fourier Transformed Infrared Spectroscopy (FTIR). Type I collagen was chosen as a model for this family of proteins, not only because of its important role in mammalian tissues, but also for its involvement in several pathologies. In order to disclose the conformational information contained in the collagen bands, the spectral characteristics of Amide III of type I collagen were related to the ones of Amide I band, performing experiments of thermal denaturation of the protein in acidic solution. Data acquired allowed to observe the protein unfolding and retrieve information about its structural arrangements during the thermal cycle. Taking as guideline the well-known behaviour of the Amide I band, we correlated the structural changes deducible from Amide I analysis with the ones detectable for Amide III band, by exploiting three spectral analysis techniques, namely 2D-correlation analysis, second derivative analysis, and peak-fitting. This approach enabled us to jointly support the obtained results and finally to assign the components of the Amide III of a typical fibrous protein, such as type I collagen, to its characteristic secondary structure.

FTIR studies of gluten matrix dehydration after fibre polysaccharide addition

FTIR spectroscopy was used to determine changes in secondary structure, as well as water state, in gluten and model doughs supplemented by four fibre polysaccharides (microcrystalline cellulose, inulin, apple pectin and citrus pectin). The gluten and model doughs were obtained from commercially available wheat gluten and model flour, respectively. The polysaccharides were used in five concentrations: 3%, 6%, 9%, 12% and 18%. Analysis of the FTIR spectra indicated that polysaccharides could be divided into two groups: first - microcrystalline cellulose and inulin, second - apple and citrus pectins that induced opposite structural changes. Changes in secondary structure concern mainly β-sheets and β-turns that form aggregated β-structures, suggesting dehydration of the gluten matrix as a result of competition for water between gluten proteins and polysaccharides. Moreover, the positive band at ca. 1226 cm^-1 in the spectra of pectin-modified samples indicates formation of 'ether' type hydrogen bonds between gluten proteins and pectins.