Relationship between Molecular Structure Characteristics of Feed Proteins and Protein <i>In vitro</i> Digestibility and Solubility

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.

Hairless canary seeds (Phalaris canariensis L.) as a potential source of antioxidant, antihypertensive, antidiabetic, and antiobesity biopeptides

“…Canary seed proteins are known to have 43% more content of sulfur-containing amino acids (e.g., cysteine and methionine) than other cereals such as wheat (Abdel-Aal et al 1997). Hence, the high content of sulfur- containing amino acids promotes the disulfide-bridges formation and, consequently, a highly packed tertiary structure (Bai et al 2016). This highly packed structure causes protein hydrolysis to take a longer time in order to increase DH significantly since peptide bonds are often encrypted and not easily accessible to the proteases.…”

Effects of protein content and the inclusion of protein sources with different amino acid release dynamics on the nitrogen utilization of weaned piglets

“…Different protein sources have differing compositions and structures, which affects their solubility and digestibility [ 11 , 27 ]. Zein is present at a high concentration in CGM, and this contains numerous hydrophobic AA and S-S and O-H bonds that promote stable α-helical structure formation [ 12 ], both of which render zein poorly soluble in water. In addition, the poor digestibility of plant-based proteins in piglets may be due to incomplete development of digestive enzymes [ 24 ].…”

“…Following the methods of Bai et al [ 12 ] and Abdallah et al [ 13 ] which was modified from the method developed by Boisen and Fernández [ 11 ], 1 g of each feed sample (measured to 0.001 g) was placed in 100 mL conical flasks, with three replicates per diet. Ten milliliters of freshly prepared 1 mg/mL pepsin (pH 2) and 0.5 mL chloramphenicol solution (0.5 g chloramphenicol in 100 mL ethanol) were added to the conical flasks, which were sealed and incubated in a water bath oscillator at 39°C for 4 h. At the end of the incubation, the conical flasks were removed, 10 mL phosphate buffer (pH 6.8) was added, and the pH was adjusted to 6.8 using 1 M NaOH.…”

“…The incubation of diets with pepsin and trypsin has been shown to be an effective means of simulating in vivo digestion in the porcine GIT [ 11 ]. In addition, the dynamics of the digestion of diets can be reflected to some extent by measuring the FAA concentrations in the in vitro residue at various time points [ 12 ]. On the basis of such studies, we have shown that CAS releases its AA faster than soybean meal (SBM) [ 6 ], and SBM releases its AA faster than corn gluten meal (CGM) [ 13 ].…”

Influence of Emerging Technologies on the Utilization of Plant Proteins

“…It leads to networks that can form gels and develop films, hold water, absorb fat, foam, emulsify, and dissolve under various pH conditions (20). Also, the relative amount of α-helices, random coils, and the α-helix/βsheet ratio in protein secondary structures of soybean and corn meals were positively correlated with protein solubility, while the percentage of β-sheet structures was negatively correlated with this same ability (23).…”