Abstract
Mid-IR techniques were used to characterize any changes that occurred on a molecular level in flaxseed that had been heated using an autoclave. The objectives were to investigate the effects of autoclave heating on differences in diffuse reflectance infrared Fourier transform (DRIFT) and synchrotron-based Fourier transform infrared microspectroscopy (SFTIRM) based measurements of the proteinα-helix toβ-sheet ratio for flaxseed (Linum usitatissimum), cv. Vimy. Hierarchical cluster analysis (CLA) and principal components analysis (PCA) were also conducted to identify molecular differences in the DRIFT spectra. Flaxseed samples were kept raw for the control or autoclaved in batches at 120°C for 20, 40 or 60 min for treatments 1, 2 and 3, respectively. DRIFT analysis of protein secondary structure ratios showed a decrease (P< 0.05) in theα-helix toβ-sheet ratio for the whole seed while the results from synchrotron SFTIRM spot data from the endosperm tissue in flaxseed showed autoclaving had the opposite effect (P> 0.05). CLA and PCA were successfully used to make distinctions between the different treatment spectra and showed enhanced sensitivity upon selection of a smaller spectral window to include only the amide I and II portion of the IR spectrum. Our results indicated that autoclaving had a great enough effect on the mid-IR spectrum of flaxseed to identify the alteredα-helix toβ-sheet ratio and subsequently differentiated between the treatments using PCA and CLA suggesting greater sensitivity of mid-IR spectral methods in identifying the effect of heat treatment on protein secondary structure. Future study is needed to quantify the relationship between protein secondary structure and protein functionality.
Highlights
Current methods of food/feed evaluation, for protein quality, are typically slow and cumbersome processes that require the destruction of a sample for any given measurement during “wet” chemical analysis
From IR spectroscopy, it may not be possible to get exact values for each secondary structure, but if all sample spectra are treated in the same manner, we can compare the results from one treatment to another [19]
The amide I band carbonyl group has different sensitivities to absorption depending on secondary structure, the number of bands it contains varies and is usually not known for certain, and the bands can be varied in shape [19]
Summary
Current methods of food/feed evaluation, for protein quality, are typically slow and cumbersome processes that require the destruction of a sample for any given measurement during “wet” chemical analysis. Part of the reason for this is that these standard methods destroy any spatial information as well as the distribution of those elements of interest [3]. These elements may be linked to degradability and digestibility in human/animals. Vibrational spectroscopy or mid-Infrared spectroscopy has the capacity to overcome some of the issues with modern food/feed characterization methods. Rather than look at the components of interest separate from one another, we can look at plant molecular structure in vivo
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