Structure of Particulate Whey Protein Gels:  Effect of NaCl Concentration, pH, Heating Temperature, and Protein Composition

Abstract

In this study whey protein gels were investigated with the aim of further testing a model and ideas developed previously. Measurements on the kinetics of the denaturation/aggregation process, dynamic rheology, gel permeability, and confocal scanning laser microscopy were combined. A broad set of experimental parameters was investigated: NaCl concentration, pH, heating temperature, and protein composition. This resulted in large variations in kinetics and the gel structures formed. The kinetics of the aggregation process determine the amount of aggregated material at the gel point, whereas the primary spatial structure is directly related to this amount of aggregated protein. The primary spatial structure essentially does not change after the gel point. The protein incorporated after the gel point induces a "thickening" of the strands in the gel network and a "decoration" of the pores in the gel. The consequence is that gel permeability decreases only slightly after the gel point but that gel rigidity increases greatly.

Stability of Biopolymer Particles Formed by Heat Treatment of β-lactoglobulin/Beet Pectin Electrostatic Complexes

“…22 The pH and ionic strength also plays a major role in determining the nature of protein aggregates formed when globular protein solutions are heated. [24][25][26][27] Thin filamentous aggregates are formed when the strength of the electrostatic repulsion between globular proteins is relatively strong (pH far from pI, low ionic strength), which leads to the formation of transparent solutions. On the other hand, particulate aggregates are formed when the strength of the electrostatic repulsion is relatively weak (pH≈pI, low ionic strength), which leads to the formation of optically opaque solutions.…”

Food Biophysics of Protein Gels: A Challenge of Nano and Macroscopic Proportions

“…Within various degrees of particulate gel structure, gel permeability is determined by the amount of aggregated protein at the gel point. Lower amounts of aggregated protein are associated with increasing gel permeability [78][79][80]. This also appears to be true for transitioning from fine-stranded to particulate gels, where the transition is associated with a progressive decrease in C o from 100 to 1 g/L [36].…”

“…A clear association is observed between water-holding properties and gel microstructure. Treatments that cause a progressive coarsening of the microstructure and moving from fine-stranded to particulate structures decrease water holding and increase permeability [75][76][77][78][79][80]. This is associated with increased moisture released during first bite evaluation [73].…”

Light Scattering Study of Turbid Heat-Set Globular Protein Gels Using Cross-Correlation Dynamic Light Scattering

“…One of the most intensively studied globular proteins is β-lactoglobulin (β-lg), which is the major component of whey and has molar mass 18,600 g/mol and radius 2 nm (2-4). The structure of the gels depends on external conditions such as pH, ionic strength, protein concentration and temperature (5,6). Close to the isoelectric point (pI = 5.2) and at high ionic strength the gels are heterogeneous and contain dense protein domains, so-called particulate gels.…”

“…In recent years the aggregation process that leads to gelation has been studied in great detail for β-lg at pH 7 using various experimental techniques (5,7,8). At pH 7 native β-lg forms dimers in equilibrium with monomers (9)(10)(11).…”