Cold-Set Whey Protein Isolate Gels: The Influence of Aggregates Concentration on Viscoelastic Properties

2011 ◽  
Vol 312-315 ◽  
pp. 1143-1148
Author(s):  
M. Vázquez da Silva ◽  
João M.P.Q. Delgado
Keyword(s):  
Whey Protein ◽  
Protein Concentration ◽  
Room Temperature ◽  
Young Modulus ◽  
Whey Protein Isolate ◽  
Protein Isolate ◽  
Holding Time ◽  
Solution Viscosity ◽  
Experimental Conditions ◽  
Weak Gels

The physical and structural properties of cold-set whey protein isolate gels are largely influenced by the protein concentration and the denaturation conditions, namely temperature and holding time. In this work, we systematically varied the protein concentration, the temperature and holding time of denaturation in order to screen their impact on the resulting heat denatured whey protein isolate (HD-WPI) solution viscosity and gel elasticity. The gelation of the HD-WPI solutions was induced, at room temperature, through the addition of magnesium chloride. Based on the assumption that solution turbidity is associated with light scattered by protein aggregates, an aggregate concentration was computed for the HD-WPI solutions. For all experimental conditions, HD-WPI solution viscosities and gels Young modulus data fall, respectively, on two single curves when plotted against the computed aggregates concentration. Three concentration regimes corresponding to non gelling solutions, weak gels and strong gels could be identified. In this study was verified that cold-set gels produced upon addition of Mg2+ had a large spectrum of elastic properties.

scholarly journals Changes of secondary structure and surface tension of whey protein isolate dispersions upon pH and temperature

2014 ◽  
Vol 32 (No. 1) ◽  
pp. 82-89 ◽  
Author(s):  
M. Tomczyńska-Mleko ◽  
E. Kamysz ◽  
E. Sikorska ◽  
C. Puchalski ◽  
S. Mleko ◽  
...  
Keyword(s):  
Surface Tension ◽  
Secondary Structure ◽  
Whey Protein ◽  
Protein Concentration ◽  
Whey Proteins ◽  
Whey Protein Isolate ◽  
Protein Isolate ◽  
Protein Solutions ◽  
The Difference ◽  
Secondary Structure Of Proteins

The secondary structure of proteins in unheated and heated whey protein isolate dispersions and the surface tension of the solutions were investigated at different pH. Heating protein solutions at 80°C results in an increase of unordered structure. Nevertheless, the difference between the contents of unordered structure in the unheated and heated samples increases with increasing pH of the solution. At low protein concentrations the surface tension decreased with increasing protein concentration to about 5 mg/ml. For the heated solution, a similar trend was observed in the decrease in the surface tension with increasing concentrations of protein. In both cases, the curves depicting the surface tension as a function of protein concentration could be fitted to the exponential function with a negative exponent, but with the heated solutions lower values of surface tension were observed. Studies on the surface tension of whey protein isolate solutions prove that the unfolding of whey proteins, revealed by changes in the secondary structure, causes a decrease in the surface tension.

Chymotrypsin selectively digests β-lactoglobulin in whey protein isolate away from enzyme optimal conditions: Potential for native α-lactalbumin purification

2012 ◽  
Vol 80 (1) ◽  
pp. 14-20 ◽  
Author(s):  
Katarina Lisak ◽  
Jose Toro-Sierra ◽  
Ulrich Kulozik ◽  
Rajka Božanić ◽  
Seronei Chelulei Cheison
Keyword(s):  
Whey Protein ◽  
High Performance ◽  
Enzyme Reaction ◽  
Whey Protein Isolate ◽  
Reversed Phase ◽  
Protein Isolate ◽  
Operating Conditions ◽  
Selective Hydrolysis ◽  
Experimental Conditions ◽  
Β Lactoglobulin

The present study examines the resistance of the α-lactalbumin to α-chymotrypsin (EC 3.4.21.1) digestion under various experimental conditions. Whey protein isolate (WPI) was hydrolysed using randomised hydrolysis conditions (5 and 10% of WPI; pH 7·0, 7·8 and 8·5; temperature 25, 37 and 50 °C; enzyme-to-substrate ratio, E/S, of 0·1%, 0·5 and 1%). Reversed-phase high performance liquid chromatography (RP-HPLC) was used to analyse residual proteins. Heat, pH adjustment and two inhibitors (Bowman–Birk inhibitor and trypsin inhibitor from chicken egg white) were used to stop the enzyme reaction. While operating outside of the enzyme optimum it was observed that at pH 8·5 selective hydrolysis of β-lactoglobulin was improved because of a dimer-to-monomer transition while α-la remained relatively resistant. The best conditions for the recovery of native and pure α-la were at 25 °C, pH 8·5, 1% E/S ratio, 5% WPI (w/v) while the enzyme was inhibited using Bowman–Birk inhibitor with around 81% of original α-la in WPI was recovered with no more β-lg. Operating conditions for hydrolysis away from the chymotrypsin optimum conditions offers a great potential for selective WPI hydrolysis, and removal, of β-lg with production of whey protein concentrates containing low or no β-lg and pure native α-la. This method also offers the possibility for production of β-lg-depleted milk products for sensitive populations.

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