Impact of hot alkali modification conditions on secondary structure of peanut protein and embedding rate of curcumin

Functional expression, purification, biochemical and biophysical characterizations, and molecular dynamics simulation of a histidine acid phosphatase from Saccharomyces cerevisiae

A histidine acid phosphatase (HAP) (PhySc) with 99.50% protein sequence similarity with PHO5 from Saccharomyces cerevisiae was expressed functionally with the molecular mass of ∼110 kDa through co-expression along with the set of molecular chaperones dnaK, dnaJ, GroESL. The purified HAP illustrated the optimum activity of 28.75 ± 0.39 U/mg at pH 5.5 and 40 ˚C. The Km and Kcat values towards calcium phytate were 0.608 ± 0.09 mM and 650.89 ± 3.6 s- 1. The half-lives (T1/2) at 55 and 60 ˚C were 2.75 min and 55 s, respectively. The circular dichroism (CD) demonstrated that PhySc includes 30.5, 28.1, 21.3, and 20.1% of random coils, α-Helix, β-Turns, and β-Sheet, respectively. The Tm recorded by CD for PhySc was 56.5 ± 0.34˚C. The molecular docking illustrated that His59 and Asp322 act as catalytic residues in the PhySc. MD simulation showed that PhySc at 40 ˚C has higher structural stability over those of the temperatures 60 and 80 ˚C that support the thermodynamic in vitro investigations. Secondary structure content results obtained from MD simulation indicated that PhySc consists of 34.03, 33.09, 17.5, 12.31, and 3.05% of coil, helix, turn, sheet, and helix310, respectively, which is almost consistent with the experimental results.

Structural and Physicochemical Characterization of Extracted Proteins Fractions from Chickpea (Cicer arietinum L.) as a Potential Food Ingredient to Replace Ovalbumin in Foams and Emulsions

Chickpeas are the third most abundant legume crop worldwide, having a high protein content (14.9-24.6%) with interesting technological properties, thus representing a sustainable alternative to animal proteins. In this study, the surface and structural properties of total (TE) and sequential (ALB, GLO, and GLU) protein fractions isolated from defatted chickpea flour were evaluated and compared with an animal protein, ovalbumin (OVO). Differences in their physicochemical properties were evidenced when comparing TE with ALB, GLO, and GLU fractions. In addition, using a simple and low-cost extraction method it was obtained a high protein yield (82 ± 4%) with a significant content of essential and hydrophobic amino acids. Chickpea proteins presented improved interfacial and surface behavior compared to OVO, where GLO showed the most significant effects, correlated with its secondary structure and associated with its flexibility and higher surface hydrophobicity. Therefore, chickpea proteins have improved surface properties compared to OVO, evidencing their potential use as foam and/or emulsion stabilizers in food formulations for the replacement of animal proteins.

Physicochemical, structural and adhesion properties of walnut protein isolate-xanthan gum composite adhesives using walnut protein modified by ethanol

Low-sugar and high-protein adhesives have broad market application prospects, while natural plant proteins have confronted technical bottlenecks due to their poor adhesion. In this study, the effects of ethanol with different concentrations (0-80%) on the adhesion properties of walnut protein isolate-xanthan gum (WNPI-XG) composite adhesives were investigated. Results showed the bonding strength of WNPI-XG treated with 40% ethanol reached 12.55 MPa, the denaturation temperature and the surface hydrophobicity increased to 87.91 and 185.07 respectively, displaying the best rheological and texture properties. It also indicated appropriate concentration of ethanol (40%) didn't change the molecular weight of WNPI-XG, but greatly strengthened the fluorescence intensity, leading changes in contents of reactive sulfhydryl groups, electrostatic forces, hydrophobic interactions, hydrogen bonds and disulfide bonds. Furthermore, the treatment also facilitated a conformation conversion of the secondary structures from β-sheet to α-helix, promoting the full unfolding of protein molecules. The microstructure analysis showed after 40% ethanol treatment, the WNPI structure was uniform, the surface of WNPI-XG adhesive was flat and smooth, combined more closely with water molecules. By analyzing the influence of ethanol treatment on adhesion of WNPI-XG, the research laid a theoretical foundation for protein modification, providing good technical references for its development and utilization.

Effect of ultrasonic treatment on the structure and functional properties of mantle proteins from scallops (Patinopecten yessoensis)

In this study, scallop mantle protein was treated by ultrasound at different powers, and then analyzed by ANS fluorescent probes, circular dichroism spectroscopy, endogenous fluorescence spectrum, DNTB colorimetry and in-vitro digestion model to elucidate the structure-function relationship. The results indicated that ultrasound can significantly affect the secondary structure of scallop mantle protein like enhancing hydrophobicity, lowering the particle size, increasing the relative contents of α-helix and decreasing contents of β-pleated sheet, β-turn and random coil, as well as altering intrinsic fluorescence intensity with blue shift of maximum fluorescence peak. But ultrasound had no effect on its primary structure. Moreover, the functions of scallop mantle protein were regulated by modifying its structures by ultrasound. Specifically, the protein had the highest performance in foaming property and in-vitro digestibility under ultrasonic power of 100 W, oil binding capacity under 100 W, water binding capacity under 300 W, solubility and emulsification capacity under 400 W, and emulsion stability under 600 W. These results prove ultrasonic treatment has the potential to effectively improve functional properties and quality of scallop mantle protein, benefiting in comprehensive utilization of scallop mantles.

Study on condition of ultrasound-assisted thermo-alkali-modified peanut protein embedding curcumin for nanoparticles

This study investigated the effects of ultrasound-assisted thermo-alkali modification on the molecular structure of peanut protein. Further, the preparation conditions involved in embedding curcumin by the modified pea protein were also studied. It was found that within the pH range of 7 < pH < 11, with an increase in pH, the content of free sulfhydryl group in peanut protein isolate gradually increased from 10.35 ± 0.63 μmol/g (pH = 7) to 18.26 ± 0.93 μmol/g (pH = 10); and the content of disulfide bonds decreased from 44.62 ± 0.48 μmol/g (pH = 7) to 34.26 ± 2.03 μmol/g (pH = 11). In the ultrasonic power range (P < 300 W), with an increase in power, the content of free mercapto group in peanut protein isolate gradually increased from 12.44 ± 0.73 μmol/g to 19.46 ± 0.24 μmol/g (P = 250 W); and the content of disulfide bonds decreased from 42.29 ± 1.24 μmol/g to 33.28 ± 0.64 μmol/g (P = 300 W). Within the temperature range of 70 °C < T < 90 °C, with an increase in temperature, the content of free sulfhydryl group in peanut protein isolate gradually increased from 10.35 ± 0.94 μmol/g (T = 70 °C) to 19.67 ± 0.68 μmol/g (T = 90 °C), and the content of disulfide bonds decreased from 45.02 ± 2.84 μmol/g (T = 70 °C) to 34.26 ± 2.03 μmol/g (T = 90 °C). Response surface test was used to optimize the preparation conditions of nanoparticles from curcumin. The results showed that the optimum parameters of ultrasonic-assisted modification of peanut protein embedding curcumin were pH = 9.8, heating temperature T = 90 °C, ultrasonic power Q = 225 W, and heating time S = 21 min. Under these conditions, the embedding rate of curcumin reached 83.27 + 1.06%, the ABTS⁺ scavenging activity generally decreases with time over the 2 days period measured in PPI solution and PPI nanoparticles (PPN), the ABTS⁺ scavenging activity decreased from 40.8%, 52.2% and 67.3% to 27.1%, 39.0% and 60.5%, respectively. Compared with pure curcumin, the antioxidant activity was increased at presence of PPI.