Power Law Behavior of Structural Properties of Protein Gels

Abstract

Whey proteins are globular, heat-sensitive proteins. The gel structure, the formation of this structure, and the rheological properties of particulate whey protein isolate (WPI) gels have been investigated. On increasing the NaCl concentration, the permeability of the WPI gels increased, indicating a coarsening of the gel structure, confirmed by confocal scanning laser microscopy pictures. Only a part of the total amount of protein present contributed to the gel network at the gel point (the primary spatial structure). Large variations were observed in the amount of aggregated material at the gel point (and thus the primary spatial structure) as a function of NaCl concentration, due to differences in the kinetics of the denaturation/aggregation process. After the gel point more protein is incorporated in the gel network by "thickening" the strands in the gel and "decorating" the pores in the gel, apparently without changing the gross spatial structure. Power law behavior was found for the permeability dependence of aged gels on the amount of aggregated material at the gel point. For various salt concentrations the curves coincided to one master curve. This power law behavior is consistent with a primary spatial structure of fractal flocs with a fractal dimensionality of 2.4. The elastic modulus is remarkably related (via a power law) with the total amount of protein contributing to the gel network, in contrast to permeability.

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

“…These observations fit a model where the gel network type is fixed at the gel point, and subsequent changes by adding additional proteins to the network or rearrangements within the network may alter physical properties but the gel type does not change [80]. It is also very clear that increasing the concentration of the gel network increases sensory firmness and fracture stress (Barrangou et al unpublished data).…”

“…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].…”

Influence of pH and ionic strength on heat-induced formation and rheological properties of cottonseed protein gels

“…The protein that remained dissolved after heating is not incorporated in the network. Therefore, these lower concentrations of aggregated protein result in a lower stiffness of the gels (Verheul et al, 1998).…”

Mineral modulation of thermal aggregation and gelation of whey proteins: from ?-lactoglobulin model system to whey protein isolate

“…Other workers have reported that only part of the total amount of proteins present in solution were aggregated at tg in the presence of NaCl [3,28]. Le Bon [17] showed that the proportion of non-aggregated b-Lg at gel point increased from 0.25 to 0.55 when the concentration of NaCl was increased from 16 to 150 mmol·L -1 (initial protein concentration = 60 g·L -1 ).…”