In-depth study of the protein molecular structures of different types of dried distillers grains with solubles and their relationship to digestive characteristics

Abstract

Background: Dried distillers grains with solubles (DDGS) have been extensively utilised in ruminant rations in western Canada and USA, and it is important to ensure their consistent quality. Traditional chemical methods do not consider the inherent structural changes of feed ingredients. Synchrotron-based Fourier transform infrared microspectroscopy (SFTIRM) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) have been utilised to detect the changes in molecular structure of several feedstuffs (e.g. barley, flaxseed and alfalfa). However, similar structural information is lacking for DDGS. The objectives of this study were to identify differences in protein molecular structures between different grains (wheat, triticale and corn) and DDGS (wheat DDGS, triticale DDGS, corn DDGS and wheat and corn blend DDGS) using SFTIRM and DRIFT and to reveal the relationship between changes in protein molecular structure and the digestive characteristics of the protein in DDGS when fed to dairy cattle.

Results: The protein molecular structure studies showed significant decreases (P < 0.01) in the amide I to amide II ratio and the α-helix to β-sheet ratio between grains and their DDGS. Protein digestive characteristics were correlated with protein molecular structures in grains and DDGS, and prediction equations were established to estimate protein digestive characteristics of DDGS using protein molecular structure parameters. For the DVE/OEB-1994 model, one of the best prediction equations was for truly absorbed protein in the small intestine (DVE) = 296.17 - 38.98 × the amide I to amide II ratio (R(2) = 0.72). For the NRC-2001 system, one of the best prediction equations was for metabolisable protein (MP) = 300.96 - 43.32 × the amide I to amide II ratio (R(2) = 0.76).

Conclusion: Protein molecular structure varies between different DDGS and their original grains, and this variation is associated with the digestive characteristics of the proteins in the DDGS and their original grains.

Keywords: DRIFT; Dried distillers grains with solubles; SFTIRM; amide I; amide II; protein structure; synchrotron; α-helix; β-sheet.