IN-DEPTH STUDY OF THE RELATIONSHIP BETWEEN PROTEIN MOLECULAR STRUCTURE AND THE DIGESTIVE CHARACTERISTICS OF THE PROTEINS IN DRIED DISTILLERS GRAINS WITH SOLUBLES

Abstract

Dried distillers grains with solubles (DDGS) have been extensively utilized in ruminant rations in western Canada. It is important to ensure the consistent quality of these DDGS. Traditional chemical methods do not consider the inherent structural changes of feed ingredients. The objectives of this study were to investigate the nutritional value of triticale and triticale DDGS in terms of chemical profile, protein and carbohydrate subfractions partitioned using the Cornell Net Carbohydrate and Protein System and energy values calculated according to NRC (2001), to evaluate the digestive characteristics of the proteins in triticale and triticale DDGS using the in situ and in vitro methods and the DVE/OEB and NRC-2001 models, to identify differences in protein molecular structures between grains (wheat, triticale and corn) and DDGS (wheat DDGS, triticale DDGS, corn DDGS and wheat and corn blend DDGS) using Synchrotron Based Fourier Transform Infrared Microspectroscopy and Diffuse Reflectance Infrared Fourier Transform Spectroscopy and to reveal the relationship between protein molecular structure and protein digestive characteristics in DDGS in dairy cattle. Triticale DDGS was significantly higher (P<0.01) in crude protein (31.5 vs. 13.3%), neutral detergent fiber (40.3 vs. 13.5%) and ether extract (6.5 vs. 1.5%) than triticale. There are significant differences in the protein and carbohydrate subfractions (P<0.05) and the ruminal degradability of dry matter (P<0.01), crude protein (P<0.01) and neutral detergent fiber (P<0.01) between triticale and triticale DDGS. Triticale and triticale DDGS had similar intestinal digestibility of rumen undegraded crude protein (P>0.05). However, triticale DDGS had higher predicted total metabolizable protein (P<0.01) and protein degraded balance (P<0.01) than triticale. The protein molecular structure study showed significant decreases (P<0.01) in the amide I to amide II ratio and the α helix to β sheet ratio from grains to 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. In conclusion, protein molecular structure varies among 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.