Fig. 1

ATR-FTIR spectra in the amide I region (1700–1600 cm⁻¹) of (a) amyloid fibrils (Aβ-42) formed in vitro (b) LGAB as received in the powder form (LGAB-AR), LGAB-AR dissolved in pH 2 and 7 (LGAB-pH2 and LGAB-pH7 respectively) and LGAB treated at pH 2 at 90 °C for 12 h (LGAB fibril) and (c) BSA heated at 90 °C for 12 h in pH 2 solution (BSA-fibril) and as received (BSA-AR). Raw data are plotted using symbols. Each spectrum was decomposed by fitting with Gaussian curves. The peak centers (in cm⁻¹) of each decomposed peak are indicated in each figure, using the color corresponding to the respective peak color. The identification of protein secondary structure for each wavenumber can be determined based on Table 2. The sum of the fitted curves is displayed as a black continuous line for each. The dotted lines are shown at low wavenumber to facilitate the identification of the major difference between spectra in the β-sheet region. Change in oligomer index with protein modifications can be observed from the change in the area under the curves of blue curves at high wavenumber