THESIS - ROC CH ... - FINAL - resubmission.pdf - University of Guelph

4.4.5 FTIR ANALYSIS
The main absorbance peaks of SPI could be seen near 1630 cm -1 , 1540 cm -1 , and 1040
cm -1 (Figure 4.14). These peaks are related to Amide I (C=O stretching), Amide II (N–H
bending), and Amide III (in phase combination of C–N stretching and N–H bending) respectively
(Lodha and Netravali 2005; Schmidt et al. 2005). The Amide I band can be used to elucidate the
changes of the secondary structure of the protein. It can be seen that a slight shift to a lower
frequency was observed after the extrusion process. Further analysis revealed that raw SPI
spectra had two underlying peaks at 1630 and 1635 cm -1 whereas after the extrusion process,
only the 1630 cm -1 band was detected. It has been suggested that the absorbance of β-sheet
structures averages near 1633 cm -1 (Barth 2007). Furthermore, the parallel and antiparallel
configurations may be predicted where antiparallel sheets have a main absorption band near
1630 cm -1 and a weak absorption band near 1685 cm -1 whereas parallel sheets typically have
higher wavenumbers in comparison but often with a missing side band (Barth 2007). Although
the main absorption was detected near 1630 cm -1 , a side band near 1685 cm -1 was not
observed in the spectra before or after extrusion. This may suggest that the SPI primarily
consisted of parallel β-sheets. Observing the Amide II band, further information of secondary
structure was elucidated. It has been suggested that antiparallel sheets and parallel sheets
predominately vibrate in the region between 1510-1530 cm -1 and 1530-1550 cm -1 respectively
(Pelton and McLean 2000). The Amide II region of raw SPI showed a prominent band at 1522
cm -1 whereas after extrusion, it was significantly shifted to 1541 cm -1 . This indicates that the
extrusion process facilitated the conversion of mixed β configurations to primarily concentrate in
parallel β-sheets.
Spectral data for pure glycerol was shown to have five distinctive peaks from 800 cm -1 to
1110 cm -1 which correspond to vibrations of C-C and C-O linkages (Lodha and Netravali 2005).
The peaks at 850 cm -1 , 925 cm -1 , and 995 cm -1 are due to the vibrations from the C-C backbone
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