Univariate and multi-variate comparisons of protein and carbohydrate molecular structural conformations and their associations with nutritive factors in typical by-products

BACKGROUND: Little attention has been paid on the inherent molecular structural effects among agricultural by-products. In this study, soybean meal (SM), wheat bran (WB), corn distillers dried grains with soluble (DDGS), dry brewer's grain (DBG), wet brewer's grain (WBG), and apple pomace (AP), which are widely used in the animal industry were selected to explore protein and carbohydrate molecular structural conformations. RESULTS: All the protein peak heights (including alpha-helixand beta-sheet) and areas were exhibited highest values in SM and lowest in AP. The SM had the highest peak area intensity of cellulosic compounds (CELC), while the remaining varieties showed the lowest absorbance level. The TSCHO (sum of structural carbohydrate (SCHO) and CELC area exhibited variations among the samples. Multivariate comparisons showed AP had no molecular structural association with other by-products within the protein amide region. Protein amides I, II and (I+II) areas, alpha-helix, beta-sheet and area ratio of protein amide and (TSCHO +TCHO) had strong relationships with CP, NDF, ADF, ADL, SCP, starch, PC, CA, CC and TDN contents. CONCLUSION: Inherent molecular structures varied among the selected by-product types and they might be used as potential predictors of nutritive factors, especially for protein structural information. (C) 2016 Society of Chemical Industry