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. 2016 Aug;29(8):1159-65.
doi: 10.5713/ajas.15.0701. Epub 2015 Nov 11.

Relationship between Molecular Structure Characteristics of Feed Proteins and Protein In vitro Digestibility and Solubility

Mingmei Bai  1   2 , Guixin Qin  1   2 , Zewei Sun  1   2 , Guohui Long  3
Affiliations

Relationship between Molecular Structure Characteristics of Feed Proteins and Protein In vitro Digestibility and Solubility

Mingmei Bai et al. Asian-Australas J Anim Sci. 2016 Aug.

Abstract

The nutritional value of feed proteins and their utilization by livestock are related not only to the chemical composition but also to the structure of feed proteins, but few studies thus far have investigated the relationship between the structure of feed proteins and their solubility as well as digestibility in monogastric animals. To address this question we analyzed soybean meal, fish meal, corn distiller's dried grains with solubles, corn gluten meal, and feather meal by Fourier transform infrared (FTIR) spectroscopy to determine the protein molecular spectral band characteristics for amides I and II as well as α-helices and β-sheets and their ratios. Protein solubility and in vitro digestibility were measured with the Kjeldahl method using 0.2% KOH solution and the pepsin-pancreatin two-step enzymatic method, respectively. We found that all measured spectral band intensities (height and area) of feed proteins were correlated with their the in vitro digestibility and solubility (p≤0.003); moreover, the relatively quantitative amounts of α-helices, random coils, and α-helix to β-sheet ratio in protein secondary structures were positively correlated with protein in vitro digestibility and solubility (p≤0.004). On the other hand, the percentage of β-sheet structures was negatively correlated with protein in vitro digestibility (p<0.001) and solubility (p = 0.002). These results demonstrate that the molecular structure characteristics of feed proteins are closely related to their in vitro digestibility at 28 h and solubility. Furthermore, the α-helix-to-β-sheet ratio can be used to predict the nutritional value of feed proteins.

Keywords: Feed; Fourier Transform Infrared Spectroscopy; Molecular Structure Characteristics; Protein; Protein In vitro Digestibility; Protein Solubility.

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Figures

Figure 1
Figure 1
Fourier transform infrared (FTIR) spectra of five conventional feed ingredient proteins (baseline, ~1,720 to 1,479 cm−1). Wavenumbers are as follows: amide I height, 1,646 cm−1; amide II height, 1,542 cm−1; amide I area, 1,720 to 1,583 cm−1; and amide II area, 1,583 to 1,479 cm−1.
Figure 2
Figure 2
Curve-fitted individual component bands (A to E) of the amide I region in Fourier transform infrared (FTIR) spectra (1,700 to 1,600 cm−1). (A) soybean meal; (B) fish meal; (C) corn distiller’s dried grains with solubles (corn DDGS); (D) corn gluten meal; (E) feather meal. Using Fourier self-deconvolution, the positions of 11 sub-peaks were subjected to Gaussian curve-fitting in the amide I band.
Figure 3
Figure 3
In vitro digestibility of five conventional feed ingredient proteins.
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