Protein structures among bio-ethanol co-products and its relationships with ruminal and intestinal availability of protein in dairy cattle

Abstract

The objectives of this study were to reveal molecular structures of protein among different types of the dried distillers grains with solubles (100% wheat DDGS (WDDGS); DDGS blend1 (BDDGS1, corn to wheat ratio 30:70%); DDGS blend2 (BDDGS2, corn to wheat ratio 50:50 percent)) and different batches within DDGS type using diffuse reflectance infrared Fourier transform spectroscopy (DRIFT). Compared with BDDGS1 and BDDGS2, wheat DDGS had higher (p < 0.05) peak area intensities of protein amide I and II and amide I to II intensity ratio. Increasing the corn to wheat ratio form 30:70 to 50:50 in the blend DDGS did not affect amide I and II area intensities and their ratio. Amide I to II peak intensity ratio differed (p < 0.05) among the different batches within WDDGS and BDDGS1. Compared with both blend DDGS types, WDDGS had higher α-helix and β-sheet ratio (p < 0.05), while α-helix to β-sheet ratio was similar among the three DDGS types. The α-helix to β-sheet ratio differed significantly among batches within WDDGS. Principal component analysis (PCA) revealed that protein molecular structures in WDDGS differed from those of BDDGS1 and between different batches within BDDGS1 and BDDGS2. The α-helix to β-sheet ratios of protein in all DDGS types had an influence on availability of protein at the ruminal level as well as at the intestinal level. The α-helix to β-sheet ratio was positively correlated to rumen undegraded protein (r = 0.41, p < 0.05) and unavailable protein (PC; r = 0.59, p < 0.05).

Figure 1

Typical full-range spectrum of DDGS with (a) peak area of amide I and amide II (at ca. 1719–1485 cm⁻¹) and (b) enlargement of amide I and II area.

Figure 2

Cluster analysis of protein molecular spectra: (a) Wheat DDGS (W), BDDGS1 (B1; 30% corn and 70% wheat) and BDDGS2 (B2, 50% corn and 50% wheat); (b) Three batches within wheat DDGS; (c) Two batches within BDDGS1; and (d) Two batches within BDDGS2.

Figure 3

Principal component analysis with 1st vs. 2nd principal component of spectra from protein molecular structures in: (a) Wheat DDGS (W), BDDGS1 (B1; 30% corn and 70% wheat) and BDDGS2 (B2, 50% corn and 50% wheat); (b) Three batches within wheat DDGS; (c) Two batches within BDDGS1; and (d) Two batches within BDDGS2.