POWER-LAW BEHAVIOR OF STRUCTURAL-PROPERTIES OF PROTEIN GELS

Whey proteins are globular, heat-sensitive proteins. The gel structure , the formation of this structure, and the rheological properties of p articulate whey protein isolate (WPI) gels have been investigated. On increasing the NaCl concentration, the permeability of the WPI gels in creased, indicating a coarsening of the gel structure, confirmed by co nfocal scanning laser microscopy pictures. Only a part of the total am ount of protein present contributed to the gel network at the gel poin t (the primary spatial structure). Large variations were observed in t he amount of aggregated material at the gel point (and thus the primar y spatial structure) as a function of NaCl concentration, due to diffe rences in the kinetics of the denaturation/aggregation process. After the gel point more protein is incorporated in the gel network by ''thi ckening'' the strands in the gel and ''decorating'' the pores in the g el, apparently without changing the gross spatial structure. Power law behavior was found for the permeability dependence of aged gels on th e amount of aggregated material at the gel point. For various salt con centrations the curves coincided to one master curve. This power law b ehavior is consistent with a primary spatial structure of fractal floc s with a fractal dimensionality of 2.4. The elastic modulus is remarka bly related (via a power law) with the total amount of protein contrib uting to the gel network, in contrast to permeability.