Detect the sensitivity and response of protein molecular structure of whole canola seed (yellow and brown) to different heat processing methods and relation to protein utilization and availability using ATR-FT/IR molecular spectroscopy with chemometrics

The objectives of this experiment were to detect the sensitivity and response of protein molecular structure of whole canola seed to different heat processing [moisture (autoclaving) vs. dry (roasting) heating] and quantify heat-induced protein molecular structure changes in relation to protein utilization and availability. In this study, whole canola seeds were autoclaved (moisture heating) and dry (roasting) heated at 120 °C for 1 h, respectively. The parameters assessed included changes in (1) chemical composition profile, (2) CNCPS protein subfractions (PA, PB1, PB2, PB3, PC), (3) intestinal absorbed true protein supply, (4) energy values, and (5) protein molecular structures (amide I, amide II, ratio of amide I to II, α-helix, β-sheet, ratio of α-helix to β-sheet). The results showed that autoclave heating significantly decreased (P < 0.05) but dry heating increased (P < 0.05) the ratio of protein α-helix to β-sheet (with the ratios of 1.07, 0.95, 1.10 for the control (raw), autoclave heating and dry heating, respectively). The multivariate molecular spectral analyses (PCA, CLA) showed that there were significantly molecular structural differences in the protein amide I and II fingerprint region (ca. 1714–1480 cm−1) among the control, autoclave and dry heating. These differences were indicated by the form of separate class (PCA) and group of separate ellipse (CLA) between the treatments. The correlation analysis with spearman method showed that there were significantly and highly positive correlation (P < 0.05) between heat-induced protein molecular structure changes in terms of α-helix to β-sheet ratios and in situ protein degradation and significantly negative correlation between the protein α-helix to β-sheet ratios and intestinal digestibility of undegraded protein. The results indicated that heat-induced changes of protein molecular structure revealed by vibration molecular spectroscopy could be used as a potential predictor to protein degradation and intestinal protein digestion of whole canola seed. Future study is needed to study response and impact of heat processing to each inherent layer of canola seed from outside to inside tissues and between yellow canola and brown canola.

Graphical abstractHeat-induced changes in protein amide I and II spectral features in typical molecular spectrum in raw canola (control), dry heated canola (roasting at 120 °C for 60 min) and moisture heated canola (autoclave heating at 120 °C for 60 min) in the region ca. 1715–1480 cm−1. Principal components analysis based on spectra (ca. 1714–1480 cm−1) obtained from the autoclave and dry heating of canola samples: Comparisons of the separate treatments (a. 4 vs. 5, b. 4 vs. 6 and c. 5 vs. 6) (4 = control, 5 = autoclave heating at 120 °C for 1 h, 6 = dry heating 120 °C for 1 h).Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Moisture heating decreased but dry heating increased the ratio of protein α-helix to β-sheet. ► Multivariate analyses detected protein molecular structure differences among the control, moisture and dry heating. ► Heat-induced changes of protein molecular structure could be used as a potential predictor to protein digestion.