Physicochemical and Dynamic Properties of Caseins Modified by Chemical Phosphorylation

Abstract

Chemical phosphorylation of bovine caseins may be useful for changing their ihysiiochkmical properties. Depending on the pH of phoiohorvlation of caseins bv ohosuhorus oxvchloride (POClA covalent bon& between phosphaie 'groul~ and diiferent spe'cific &ino acids were formed. After casein phosphorylation, intermolecular associations may occur, as shown by electrophoresis. The solubility of modified casein was increased near the isoelectric point (pHi) and decreased at alkaline and acidic pH. In the presence of Ca++ at alkaline pH, the solubility of phosphorylated casein was lower than that of the control. Rheological parameters appeared to be efficient indices of structural changes occurring in proteins as a result of chemical modifications. Electron spin resonance studies showed that the flexibility of phosphorylated casein was higher than that of the control. phosphorylated casein was measured as a function of the level of phosphorylation and of the pH and ionic strength of the medium. The influence of the level of phosphorylation, pH and casein concentration on chain flexibility was evaluated by electron spin resonance (ESR) spectrometry. Viscosity measurements were also performed, in order to determine the flow behavior of casein solutions and their intrinsic viscosity. MATERIALS & METHODSCasein preparation Native bovine casein was obtained from skim milk by precipitation at the isoelectric point (pH 4.6) using 1M hydrochloric acid solution. The precipitate was washed, solubilized at pH 7 with sodium hydroxide, precipitated again and washed three more times. Finally, the casein was solubilized again at pH 7, freeze-dried and stored at 4°C in hermetically sealed bags.

Some Functional Properties of an Enzymatically Phosphorylated Cowpea (Vigna unguiculata)Globulin Isolate

“…This makes them more available for protein-protein interactions, with a concomitant decrease in solubility when compared to that of the native proteins. 16) The significant (p S 0.05) decrease in EAI value (except at pH 5) that was observed for the phosphorylated proteins is an indication of decreased interfacial film formation. Studies with other proteins (i.e., soybean and bovine serum albumin) have indicated that increased charge repulsion reduced the rate of protein adsorption, the quantity of protein adsorbed, and the strength of the adsorbed protein film.…”

“…4 ) The decreased solubility of phosphorylated proteins at pH < 4 can be attributed to a decreased net positive charge due to the addition of negatively charged phosphate groups. 16) Similarly, at pH > 6, the putative open structure of the phosphorylated proteins as a result of the higher net negative charge increases the accessibility of hydrophobic groups. This makes them more available for protein-protein interactions, with a concomitant decrease in solubility when compared to that of the native proteins.…”

“…23 ) Electrostatic interactions within and between proteins are maximized at their pI value, and decrease as pH values deviate from pI. 16) An increase in the covalent attachment of negatively charged phosphate groups in proteins, therefore, would have had a greater effect on the net electrostatic forces at pH values near to the pI value than at pH values far from it. Thus, the significant changes in FC occurred under conditions close to the pI value.…”

Separation and characterization of major milk proteins from Algerian<br>Dromedary (Camelus dromedarius)

“…Similar peptide fragments were not obtained when CNs were treated with different proteases. The major protein components of camel milk, α S1 -and β-CNs, contain different numbers of covalently attached phosphate groups bound to residues of serine and threonine (Dickson and Perkins, 1971;Medina et al, 1992). The bound phosphate groups influence many functional properties of these proteins, including their digestibility, bioavailability of divalent cations and immunogenicity (Tezcucano et al, 2007).…”

Functional properties of β-lactoglobulin phosphorylated in the presence of different aliphatic amines

“…Chemical phosphorylation may provide a powerlul tool for a change of the physicochemical properties of the proteins (Yoshikawa et al, 1981;Hirotsuka et al, 1984;Huang and Kinsella, 1987;Chobert et al, 1989a;Matheis, 1991). lt may be very efficient if the reaction conditions are carefully designed (Medina et al, 1992;Sitohy et al, 1994). Recently, it was found possible to phosphorylate proteins under mild conditions avoiding oligomerization (Sitohy et al, 1994(Sitohy et al, , 1995.…”