In summary, different types and sources of the co-products from ethanol processing based cereal grain as energy feed- stock in this study showed difference in protein nutrient and utilization profiles and protein internal structural makeup. Although the CLA and PCA analyses revealed similarity in protein molecular spectra, some protein molecular spectral feature of the co-products have relationship with protein nutrient utilization and availability to some extent. The dif- ference in protein nutritional values in corn co-product and barley co-products may be mainly explained by different original cereal grains as energy feedstock and different pro- cessing methods. The difference in protein molecular struc- ture parameters may account for variations on nutritional values and biological behaviors.