Electrostatic Effects on Physical Properties of Particulate Whey Protein Isolate Gels

Abstract

Physical properties of particulate whey protein isolate gels formed under varying electrostatic conditions were investigated using large strain rheological and microstructural techniques. The two treatment ranges evaluated were adjusting pH (5.2‐5.8) with no added NaCl and adjusting the NaCl (0.2‐0.6 M) at pH 7. Gels (10% protein w/v) were formed by heating at 80C for 30 min. The large strain properties of fracture strain (γf), fracture stress (σf), and a measure of strain hardening (R0.3) were determined using a torsion method. Gel microstructure was evaluated using scanning electron microscopy (SEM) and gel permeability (Bgel). Overlaying σf and γf curves for pH and NaCl treatments demonstrated an overlap where gels of equal σf and γf could be formed by adjusting pH or NaCl concentration. The high fracture stress (σf∼ 23 kPa and γf∼ 1.86) pair conditions were pH 5.47 and 0.25 M NaCl, pH 7.0. The low fracture stress (σf∼ 13 kPa and γf∼ 1.90) pair conditions were pH 5.68 and 0.6 M NaCl, pH 7.0. The 0.25 M NaCl, pH 7 treatment demonstrated higher R0.3 values than the pH 5.47 treatment. When the sulfhydryl blocker n‐ethylmaleimide was added at 2 mM to the 0.25 M NaCl, pH 7 gel treatment, its rheological behavior was NSD (p>0.05) to the pH 5.47 gel treatment, indicating disulfide bond formation regulated strain hardening. Altering surface charge or counterions, and disulfide bonding, was required to produce gels with similar large strain rheological properties. An increase in gel permeability coincided with an increase in pore size as observed by SEM, independent of rheological properties. This demonstrated that at the length scales investigated, microstructure was not linked to changes in large strain rheological properties.

EFFECT OF NaCl ON GELATION CHARACTERISTICS OF ACID- AND ALKALI-TREATED PACIFIC WHITING FISH PROTEIN ISOLATES

“…1994). McGuffey and Foegeding (2001) investigated the physical properties of particulate whey protein isolate gels under varying electrostatic conditions and proposed that disulfide bond formation affected the strain values of gels.…”

Characterization and acid-induced gelation of butter oil emulsions produced from heated whey protein dispersions

“…At temperatures above 65 1C, the globular structure of major whey protein unfolds and exposes hydrophobic and sulphydryl groups. At the same time, protein aggregation, promoted by attractive interactions and disulphide bonds formation, creates a threedimensional network (Twomey, Keogh, Mehra, & Kennedy, 1997 texture of heat-set whey protein gels depend on protein concentration, salts and pH during heat treatment (Foegeding, 1998;McGuffey & Foegeding, 2001;Puyol, Perez, & Horne, 2001). Opaque particulate gels with poor water holding capacity are produced at pH close to the isoelectric point of b-lactoglobulin, whereas translucent fine-stranded gels with good water holding capacity are produced in more alkaline conditions (Stading & Hermansson, 1990).…”

An ISO‐Protein Model Food System for Evaluating Food Texture Effects

“…). Changes in pH, ionic strength, and type of ion (e.g., NaCl or CaCl 2 ) causes variations in the size and shape of primary and secondary protein aggregates that alter gel texture (Mulvihill and Kinsella ; McGuffey and Foegeding ; Chantrapornchai and McClements ; Ako et al . ).…”