The objective of this study was to study impact of ethanol (CAS # 64-17-5) processing on association of protein structures at a molecular level to protein nutrient utilization and availability of different co-products from cereal grains as energy feedstocks in China and to identify the correlation between protein molecular structures and protein nutritional profiles of co-products from ethanol bioprocessing in China in terms of: 1) protein chemical profiles; 2) protein subfractions; 3) total digestible protein; 4) protein degradation and estimated intestinal CP digestibility. The proteins molecular structure were determined using FT/IR-ATR molecular spectroscopy. The protein 2nd structure alpha-helix and beta-sheet were modeled based on amide I component peaks centered at ca. 1650 and 1630 cm(-1), respectively identified by using 2nd derivative function. The protein subfractions were analyzed used CNCPS system. Total digestible protein were estimated according to a summary chemical approach in NRC model. Protein degradation and intestinal CP digestibility were determined using in situ nylon bag technique and three-step in vitro method, respectively. The results indicated that co-products from corn and barley differed in both protein nutritional profiles and protein structure parameters in terms of alpha-helix, beta-sheet spectral intensity and their ratio and amide I, amide II spectral intensity and their ratio. Protein amide II height had a weakly positive correlation with (p < 0.05) PB2 fraction with R = 0.53, but that other protein amide parameters had no correlation with (p > 0.05) PA, PB1, PB3 and PC fractions. Protein amide II height had a positive correlation with (p < 0.05) TDN with R = 0.74. Protein amide II height has a negative correlation with (p < 0.05) protein degradability (R_DCP) with R = -0.67, and a positive correlation with (p < 0.05) intestinal protein digestibility (I_DCP) with R = 0.60, and a positive correlation with (p < 0.05) total tract available protein (T_ACP) with R = 0.58. For protein secondary structure, the alpha-helix to beta-sheet ratio was negatively correlated with (p < 0.05) total protein digestibility (T_DCP) with R = -0.56 and positively correlated with (p < 0.05) total digestible crude protein (tdCP) with R = 0.55. In conclusion, the relationship between mid-IR spectroscopic data and nutritional profiles and digestibility parameters illustrated that the co-products intrinsic structures are closely related to nutritive quality, nutrient utilization and digestive behavior. (C) 2014 Elsevier Ltd. All rights reserved.