Relationship of protein structural conformation to protein functional property, buffer and water solubility, rumen digestive behaviors, and intestinal availability of common feeds in ruminants
The objectives of this study were to determine the relationship between the intrinsic molecular structures of protein feeds and their protein solubility, and rumen and intestinal digestibility in dairy cattle. The feeds investigated were barley, corn, oat, wheat, lentil, peas, canola meal, expeller meal (extruded canola meal), soybean meal, mill feeds (pelleted byproducts from cereal grains), lantic sugar beet pulp, blood meal and meat meal. The protein molecular structure makeup of the feeds was revealed using attenuated total reflectance-Fourier transform infrared molecular spectroscopy (ATR-FTIR). The spectral data on unique bands such as amid I, amide II, and protein secondary structures such as α-helix and β-sheet and their ratios were analyzed for differences in intrinsic molecular structures. Moreover, multivariate analysis, agglomerative hierarchical cluster analysis and principal component analysis were computed on the molecular spectral data to distinguish the overall differences in intrinsic molecular structures among the feeds. The protein functional property, solubility, rumen and intestinal digestibility were determined directly using dairy cattle. The PROC MIXED procedure of SAS was used to analyze the univariate spectra data, water-and buffer-based protein solubility, rumen and intestinal protein digestibility. Pearson correlation coefficients between the protein spectral data and protein digestibility were computed using the PROC CORR procedure. A stepwise multiple regression procedure of SAS was carried out to determine which of the protein molecular structural features could be used to estimate protein solubility, degradability and digestibility of the prairie feeds. The ‘stepwise’ option was used with variable selection criteria: ‘SLENTRY = 0.05, SLSTAY = 0.05’. The variance inflation factor (VIF) option was used to detect and avoid collinearity among the independent variables. The results showed a large variation in water-and buffer-based protein solubility; ruminal, intestinal and total protein digestibility; and in the inherent structure makeup of protein among the feeds. The protein structural conformation in terms of amide I-and II and protein secondary structures (α-helix and β-sheet) were strongly correlated with protein solubility, and ruminal and intestinal digestibility in dairy cattle. The protein structure spectral parameters of amid II area and β-sheet height could be used to predict protein intestinal and total digestible content of prairie feeds in dairy cattle. In conclusion, this study report a novel data on protein molecular structure and showed that protein structural makeup was associated with protein nutritional value and digestive behavior in dairy cattle.
Protein molecular structure; molecular spectroscopy; nutrient availability; metabolic characteristics of protein; ruminants