Exploring the use of FTIR Amide I band deconvolution to investigate protein secondary structure and texturisation during high moisture extrusion

Fourier transform infrared spectroscopy (FTIR) combined with Amide I band deconvolution has been used to investigate protein structural changes occurring during high moisture extrusion processing (HMEP). However, it is a sensitive, user-dependent technique that has sparked debate over its appropriate analytical approach. This paper aims to assess the suitability of FTIR Amide I band deconvolution to investigate protein structural changes in fava bean protein concentrate (FBPC) caused by temperature treatment and/or HMEP at different temperatures (110 °C, 135 °C and 165 °C), and to explore its relationship with the texturisation level of the obtained products. Influence of sample preparation and parameter selection during FTIR deconvolution procedure was also explored. To do so, FBPC was heated in a convection oven or subjected to HMEP at different temperatures (110, 135 or 165 °C), and Fourier self-deconvolution (FSD) and second derivative (SD) were explored as band-narrowing methods to analyse protein conformation from FTIR spectra. FTIR Amide I band deconvolution showed high sensitivity to sample preparation and parameter selection during FSD and SD analytical procedure. Results suggested that HMEP caused the denaturation of β-sheet forms present initially in FBPC, and an increase of other structures including intermolecular β-sheet and/or aggregates-probably due to the formation of new intermolecular bonds. Moreover, although higher temperature during HMEP enhanced fibre-like structure formation, texturisation level could not be directly related to the protein conformation of the final high moisture extrudates (HME), since no significant differences were observed between protein secondary structure of HME under the studied conditions.