Heat-Induced Changes in Protein Molecular Structure Associated with Rumen Degradation of Oat Grains in Dairy Cows Detecting By Vibrational Molecular Spectroscopy

Heat processing may simultaneously affect protein rumen degradation and protein intestinal digestion by altering molecular protein structure in seeds. Attenuated Total Reflectance Fourier transform vibrational molecular spectroscopy (ATR-Ft/VMS) is a novel technique that reveals molecular structural features, increasing the understanding of feed structures at cellular level and new level of analytical information. The objective of this study was to reveal the change from heat-related feed processing in the molecular protein structure of oat grains: CDC Nasser and CDC Seabiscuit. Oat grains were sampled from harvested plots (n = 2) grown in 2014 and 2015. Each oat variety was equally divided into 4 portions and performed in one treatment: raw, dry-heating, autoclave heating or microwave irradiation. Samples were rolled (gap size 1.78 mm) for in situ incubation and ground through 0.5 mm screen for molecular spectral analysis. Amide I (1720 – 1577 cm^-1) and amide II (1577 – 1486 cm^-1) area intensities and peak heights, and secondary protein structures α-helices and β-sheets heights were measured in the region at ca. 1720 – 1486 cm^-1 were quantified using OMNIC 7.3 software. Rumen degradation was performed using dairy cows equipped with rumen cannulae. Spectral data were analyzed using univariate analysis of recording peak parameters. Spearman correlation was performed after normality test. Multiple regressions were performed using PROC REG of SAS 9.4. Autoclave heating increased (P < 0.001) Amide I:Amide II area ratio and heat processing methods increased (P < 0.001) Amide I:Amide II height ration comparing to raw. The α-helix and β-sheet heights were lower for autoclave heating comparing to dry heating; however these treatments were statistically similar with raw. Rate of degradation of crude protein (KdCP) was positive correlated with α-helix (r = 0.54; P = 0.028) and β-sheet (r = 0.59; P = 0.015); effective degradability (EDCP) was strongly positive correlated with Amide I (r = 0.75; P < 0.001) and Amide II (r = 0.67; P < 0.001) areas, α-helix (r = 0.75; P < 0.001) and β-sheet (r = 0.86; P < 0.001). Multiple regressions were obtained: KdCP = -22.66 + 205.68 x β-sheet (R² = 0.34; P = 0.015); EDCP = -52.18 + 568.89 x β-sheet (R² = 0.69; P < 0.001). It can be concluded that heat-related feed processing affects molecular protein structures, the difference can be detected by ATR-Ft/VMS and protein molecular structure profile could be used as a predictor to estimate degradation kinetics of CP.