Abstract:

The conditions necessary to form an assocd. complex between whey protein isolate (WPI) and enzymically modified pectin in water, at pH values above the isoelec. point of the protein, have been documented. The existence of the complex is not easily verified and its characterization in soln. is even more complicated, since the structure is an intermediate entity between the non-interacting, incompatible aq. sol. mixt. of the biopolymers, and a strongly interacting coacervated pptg. complex. Evidence for the formation of this assocd. complex is provided from confocal laser scanning microscope images and rheol. behavior of the aq. mixts. The assocd. complex is characterized by small fluorescent "patches" interpreted as small aggregates. The viscosity of this soln. is greater than that of its individual biopolymer constituents, indicating a synergy of attractive interactions that occurs in the soln. While individually, the pectin and the WPI solns. at the studied range of concns. exhibit moderately non-Newtonian behavior, at sp. wt. ratios, mixts. of the two behave either as highly entangled polymeric structures or as weak gels. The values of the storage modulus G' are equal to or greater than those of the loss modulus G''. We conclude that the assocd. complexes are formed at pH 6, and at 4 wt% WPI with a pectin concn. ranging from 0.1 to 0.75 wt%. The influence of the charge distribution (degree of order of the carboxylic groups) of pectin on the assocd. complex was also investigated, and it was found that the more "ordered" pectin (U63) favors the formation of the assocd. sol. complex. [on SciFinder(R)]