Whey Protein Isolate Solutions Research Articles

Turbidity and Rheological Properties of Gels and Sols Prepared by Heating Process Whey Protein

“Process whey protein” was prepared by heating bovine milk whey protein isolate solution at neutral pH under salt-free conditions. The process whey protein solution, being clear, was heated at various pHs (2.0 to 11.0) and NaCl concentrations (0 to 200 mM), and the turbidity and gel properties of the products were then examined. For comparison, the properties of the whey protein isolate treated under the same conditions were measured. The whey protein isolate formed a transparent gel or sol below pH 3 and above pH 7 at low NaCl concentration after heating, but the process whey protein formed transparent gels and sols over a wider range of pH and NaCl concentrations than those of the whey protein isolate. More elastic, firmer, and denser gels were obtained from the process whey protein than from the whey protein isolate. The process whey protein provides a novel food material with useful properties.

β‐Lactoglobulin Separation from Whey Protein Isolate on a Large Scale

ABSTRACTA method for obtaining large quantities of β‐lactoglobulin (β‐Lg) from commercial whey protein isolate (WPI) was developed. β‐Lg was separated from the rest of the whey proteins in a solution of 15% (W:W) WPI in distilled water adjusted to pH 2 and 7% NaCl. β‐Lg was then separated from NaCl using diafiltration. The results indicate that more than 65% of the β‐Lg originally in the WPI solution was recovered. The purity of the β‐Lg was greater than 95%.

Composite blends from heat-denatured and undenatured whey protein: Emulsifying properties

Abstract A solution of commercial whey protein isolate was heat-denatured (DWPI) and combined in various ratios with undenatured whey protein isolate (WPI). Emulsions with an oil volume fraction varying from 0·05 to 0·26 were prepared from these mixtures using a lab scale valve homogenizer. The protein content of the aqueous phase was standardized to 3%. The emulsifying activity index of the protein mixtures was determined and the emulsions were analysed for resistance to stirring-induced coalescence, separation stability, viscosity and age thickening. Higher levels of DWPI in the protein blend and higher oil volume fractions of the emulsion increased emulsifying activity, emulsion viscosity and stability. However, these emulsions showed evidence of age thickening. Resistance to stirring-induced coalescence was improved by increasing the proportion of DWPI in the blend and by reducing the oil content of the emulsion. The roles of heat-denatured and undenatured whey proteins in emulsified systems appeared complementary.

EFFECT OF EMULSION DROPLETS ON THE RHEOLOGY OF WHEY PROTEIN ISOLATE GELS

ABSTRACTThe effects of droplet size and emulsifier type on the rheology of whey protein isolate (WPI) gels containing emulsion droplets was studied. Gels were prepared by dispersing droplets of corn oil (20 wt%, d32= 0.7 – 4 μm) in a 10 wt% WPI solution (pH 7.0, 50 mM NaCl), and heating at 90C for 15 min. Gel strength was determined by measuring the stress of gels at 20% compression using an Instron Universal Testing Machine. Droplets stabilized by WPI increased the gel strength, those stabilized by non‐ionic surfactants (Tween 20 and Triton X‐100) decreased it slightly, and those stabilized by SDS decreased it drastically. Gel strength increased as the droplet size decreased for droplets stabilized by WPI, but was relatively insensitive to the size of droplets stabilized by the small molecule surfactants. These observations may be explained in terms of the interactions between the emulsifiers and the protein network. Droplets coated with emulsifiers which can be incorporated into the protein network reinforce the structure and so increase gel strength, whereas droplets coated with emulsifiers which cannot be incorporated into the protein network disrupt the three dimensional structure of the gel and decrease its strength.

Structural and Functional Properties of Caseinate and Whey Protein Isolate as Affected by Temperature and pH

ABSTRACTThe structural properties, i.e., active sulfhydryl (SH), flexibility and hydrophobicity, and functional properties, i.e., solubility, emulsion activity (EA), emulsion stability (ES), foam overrun (FO) and foam stability (FS), of commercial sodium caseinate (SC) and whey protein isolate (WPI) solutions were investigated at pH 6, 7 and 8 and at 25, 55 and 65°C. WPI contained a higher concentration of active SH and was more hydrophobic than SC. WPI provided comparable solubility and EA, lower FO, but higher FS than SC. Temperature and pH effects on the two proteins were somewhat inconsistent.

Influence of pH and ionic environment on thermal aggregation of whey proteins

A solution of whey protein isolate (WPI) was heated at 1.6 degrees C/min from 25 to 96 degrees C to monitor protein-protein aggregation by turbidity measurement. Protein aggregation showed a single transition (71 degrees C) at pH 5.5, two transitions (76 and 88 degrees C) at pH 6.0, and no transition above pH 6.5. The addition of 0.6 M NaCl induced a second transition (77 degrees C) at pH 5.5 and promoted protein-protein interaction above pH 6.5. The aggregation temperatures decreased to a minimum by 20 mM NaCl and 5-10 mM CaCl2. Protein-protein interaction was suppressed at 5 mM sodium phosphate and gradually recovered at increasing sodium phosphate concentrations. In conclusion, low ionic strengths of cations and low pH facilitated protein-protein association, while phosphate promoted protein aggregation only in conjunction with NaCl.

The effect of pH, thiol reagent and time on properties of urea-induced whey protein gels

Solutions of whey protein isolate (11.0% by weight) in 6 mol/dm 3 urea spontaneously formed gels at 25°C. The gelling rate increased exponentially, but the gels became less elastic and more fragile, as the pH was increased from 7 to 10. The addition of N-ethylmaleimide at <3 mmol/dm 3 increased gel strength, whereas gelation was inhibited above 5 mmol/dm 3. Gel strength increased by 25% during storage at 25°C for 7 days.

Comparative emulsifying properties of sodium caseinate and whey protein isolate in 18% oil in aqueous systems

SummaryBoth whey protein isolate (WPI) and Na caseinate gave similar emulsion capacity-concentration profiles at pH 7. The emulsion capacity of aqueous solutions of WPI was relatively independent of pH while the values for caseinate fell in the isoelectric region. Saline (7·59 g/1) compared with aqueous solutions improved emulsion capacity, particularly above pH 7. At low concentration, WPI had greater emulsifying capacity and gave finer globule dispersion than sodium caseinate. Increase in emulsifier concentration, within a certain range, increased stability, improved dispersion and reduced capacity. Ethanol up to about 20% w/w improved the emulsion capacity of both proteins while at 50% the phases separated. Heat treatment (&gt; 65 °C) of WPI solution before emulsion formation impaired capacity and stability. Heat treatment of preformed WPI emulsions did not have the same effect. Na caseinate and WPI each formed a thin continuous layer of relatively uniform thickness over the oil globule surfaces while denatured WPI appeared aggregated and relatively unevenly distributed at the oil-aqueous interface.