Molecular spectroscopic investigation on fractionation-induced changes on biomacromolecule of co-products from bioethanol processing to explore protein metabolism in ruminants

• Fractionation processing changed the molecular structural spectral profiles.
• These changes negatively affected the metabolic characteristics of protein and true protein supply.
• Molecular spectral features of the fractions could be used to predict true protein nutritive value.

Fractionation processing is an efficient technology which is capable to redesign/redevelop a new food or feed product with a specified chemical and nutrient profile. This processing technique was able to produce four different fractions (called “A”, “B”, “C”, “D” fractions/treatments) with different nutrient profile form a co-product of bioethanol processing [wheat dried distillers grains with soluble (DDGS)]. To date, there is no study on the effect of fractionation processing on inherent molecular structure of different fractions and how the processing-induced structural change affect the metabolic characteristics of protein and nutrient availability. The objectives of this experiment were to: (1) investigate the effect of fractionation processing on changes of protein functional groups (amide I, amide II, and their ratio) and molecular structure (modeled α-helix, β-sheet, and their ratio), and (2) study the relationship between the fractionation processing-induced changes of protein molecular structure and nutrients availability as well as the metabolic characteristics of protein. The hypothesis of this study was that the fractionation processing changes the molecular structure and such changes affect the metabolic characteristics of protein. The protein molecular structure spectral profile of the fractions A, B, C and D were identified by Fourier-transform infrared attenuated total reflection spectroscopy (FT/IR-ATR). The results showed that the fractionation processing significantly affected the protein molecular spectral profiles. The differences in amide I to amide II peak area and height ratios were strongly significant (P < 0.01) among the treatment fractions, ranging from 4.98 to 6.33 and 3.28 to 4.00, respectively. The difference in the modeled protein α-helix to β-sheet ratio was also strongly significant (P < 0.01) among the treatment fractions. Multivariate molecular spectral analysis with cluster (CLA) and principal component analyses (PCA) showed that there are no clear distinguished clusters and ellipses among the fractions (A, B, C and D) in the protein amide I and II region ca. 1726–1485 cm−1. The correlation study showed that the modeled α-helix to β-sheet ratio tended to have a negative correlation with truly absorbed rumen undegraded protein (ARUPDVE: r = −0.944, P = 0.056 < 0.10) and total truly absorbed protein in the small intestine (DVE: r = −0.946, P = 0.054 < 0.10), but there was no correlation between the α-helix to β-sheet ratio and the degraded protein balance (DPBOEB: P = 0.267 < 0.10). In conclusion, the fractionation processing changed the molecular structural spectral profiles in terms of amide I to II ratio and α-helix to β-sheet ratio. These changes negatively affected the metabolic characteristics of protein and true protein supply. These results indicated that spectral features of different fractions could be used as a potential tool to predict true protein nutritive value.

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