Effect of extraction method on the calcium binding capacity of faba bean globulin fractions at various pH.

Faba bean ingredients are rich in proteins and good sources of calcium (Ca), although containing phytic acid (PA) molecules. PA, a polyphosphate compound, can affect the bioavailability of minerals/proteins through complex formation. This study evaluates the impact of two extraction processes, Alkaline Extraction-IsoElectric Precipitation (AE-IEP) and Sequential Extraction (SE), on the ability of faba bean globulin systems to bind added calcium ions. Increasing concentrations of CaCl2 were introduced into 2.5% (w/v) protein dispersions at pHs 4.5, 5.5, 6.5, and 7.5, and free Ca monitored. Near the isoelectric point of globulin (pH âˆ¼ 4-5), Ca binding capacity was found to be low. At higher pHs, significant Ca chelation occurred, initially attributed to free PA binding sites, resulting in the formation of insoluble complexes and subsequent protein precipitation. The AE-IEP globulin fraction exhibited a higher Ca binding capacity than the SE globulin, attributed to its higher PA and lower initial Ca concentrations.

Modulating Weak Protein-Protein Cross-Interactions by the Addition of Free Amino Acids at Millimolar Concentrations.

In this paper, we quantify weak protein-protein interactions in solution using cross-interaction chromatography (CIC) and surface plasmon resonance (SPR) and demonstrate that they can be modulated by the addition of millimolar concentrations of free amino acids. With CIC, we determined the second osmotic virial cross-interaction coefficient (B23) as a proxy for the interaction strength between two different proteins. We perform SPR experiments to establish the binding affinity between the same proteins. With CIC, we show that the amino acids proline, glutamine, and arginine render the protein cross-interactions more repulsive or equivalently less attractive. Specifically, we measured B23 between lysozyme (Lys) and bovine serum albumin (BSA) and between Lys and protein isolates (whey and canola). We find that B23 increases when amino acids are added to the solution even at millimolar concentrations, corresponding to protein/ligand stoichiometric ratios as low as 1:1. With SPR, we show that the binding affinity between proteins can change by 1 order of magnitude when 10 mM glutamine is added. In the case of Lys and one whey protein isolate (WPI), it changes from the mM to the M range, thus by 3 orders of magnitude. Interestingly, this efficient modulation of the protein cross-interactions does not alter the protein's secondary structure. The capacity of amino acids to modulate protein cross-interactions at mM concentrations is remarkable and may have an impact across fields in particular for specific applications in the food or pharmaceutical industries.

Specific effect of calcium ions on thermal gelation of aqueous micellar casein suspensions.

Aqueous suspensions of micellar casein (MC) gel when heated above a critical temperature that depends on the pH. The effect of adding CaCl2 and EDTA on thermal gelation was studied in order to assess the effect of increasing or decreasing the amount of bound Ca2+ on the process. The effect of adding NaCl was investigated in order to distinguish the effect of Ca2+ binding from the effect of screening of electrostatic interactions. Shear moduli were measured as a function of the temperature during heating ramps up to 90 °C. Gel formation was characterized by a sharp increase of the storage modulus at a critical temperature (Tc). In most cases, prolonged heating at 90 °C did not cause a significant increase of the gel stiffness. Addition of CaCl2 caused a decrease of Tc, whereas addition of NaCl caused an increase of Tc. Chelation of Ca2+ by EDTA led to a strong increase of Tc even if the fraction of chelated Ca2+ was small and the micelles remained intact. The gel stiffness was found to increase weakly with increasing CaCl2 concentration up to 20 mM. The gels persisted during cooling to 20 °C with an increase of the elastic modulus by a factor between 4 and 6 depending on the CaCl2 concentration. The results demonstrate that Ca2+ plays a crucial role in thermal MC gelation.