Heat-induced changes to lipid molecular structure in Vimy flaxseed: Spectral intensity and molecular clustering

Autoclaving was used to manipulate nutrient utilization and availability. The objectives of this study were to characterize any changes of the functional groups mainly associated with lipid structure in flaxseed (Linum usitatissimum, cv. Vimy), that occurred on a molecular level during the treatment process using infrared Fourier transform molecular spectroscopy. The parameters included lipid CH3 asymmetric (ca. 2959 cm−1), CH2 asymmetric (ca. 2928 cm−1), CH3 symmetric (ca. 2871 cm−1) and CH2 symmetric (ca. 2954 cm−1) functional groups, lipid carbonyl CO ester group (ca. 1745 cm−1), lipid unsaturation group (CH attached to CC) (ca. 3010 cm−1) as well as their ratios. Hierarchical cluster analysis (CLA) and principal components analysis (PCA) were conducted to identify molecular spectral differences. 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. Molecular spectral analysis of lipid functional group ratios showed a significant decrease (P < 0.05) in the CH2 asymmetric to CH3 asymmetric stretching band peak intensity ratios for the flaxseed. There were linear and quadratic effects (P < 0.05) of the treatment time from 0, 20, 40 and 60 min on the ratios of the CH2 asymmetric to CH3 asymmetric stretching vibration intensity. Autoclaving had no significant effect (P > 0.05) on lipid carbonyl CO ester group and lipid unsaturation group (CH attached to CC) (with average spectral peak area intensities of 138.3 and 68.8 IR intensity units, respectively). Multivariate molecular spectral analyses, CLA and PCA, were unable to make distinctions between the different treatment original spectra at the CH3 and CH2 asymmetric and symmetric region (ca. 2988–2790 cm−1). The results indicated that autoclaving had an impact to the mid-infrared molecular spectrum of flaxseed to identify heat-induced changes in lipid conformation. A future study is needed to quantify the relationship between lipid molecular structure changes and functionality/availability.

► Molecular spectral analysis of lipid functional group ratios showed a significant decrease (P < 0.05) in the CH2 asymmetric to CH3 asymmetric stretching band peak intensity ratios for the flaxseed.
► There were linear and quadratic effects (P < 0.05) of the treatment time from 0, 20, 40 and 60 min on the ratios of the CH2 asymmetric to CH3 asymmetric stretching vibration intensity.
► Autoclaving had no significant effect (P > 0.05) on lipid carbonyl CO ester group and lipid unsaturation group (CH attached to CC) (with average spectral peak area intensities of 138.3 and 68.8 IR intensity units, respectively).
► Multivariate molecular spectral analyses, CLA and PCA, were unable to make distinctions between the different treatment original spectra at the CH3 and CH2 asymmetric and symmetric region (ca. 2988–2790 cm−1).
► The results indicated that autoclaving had an impact to the mid-infrared molecular spectrum of flaxseed to identify heat-induced changes in lipid conformation.
► A future study is needed to quantify the relationship between lipid molecular structure changes and functionality/availability.