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Effect of ß-Lactoglobulin A and B Whey Protein Variants on the Rennet-Induced Gelation of Skim Milk Gels in a Model Reconstituted Skim Milk System

M. A. Meza-Nieto^*, B. Vallejo-Cordoba^*, A. F. González-Córdova^*, L. Félix and F. M. Goycoolea^,1

^* Laboratory of Dairy Science and Technology, and
Laboratory of Biopolymers, Centro de Investigación en Alimentación y Desarrollo, AC (CIAD, AC), P.O. Box 1735 Hermosillo, Sonora, 83000 Mexico

¹ Corresponding author: fgoyco{at}cascabel.ciad.mx

The effect of fortifying reconstituted skim milk with increasing levels of the ß-lactoglobulin (ß-LG) genetic variants A, B, and an A-B mixture on rennet-induced gelation was studied by small deformation-sensitive rheology. Free-zone capillary electrophoresis and high-sensitivity oscillatory rheology were used to elucidate the role of potential heterotypic associative interactions between whey proteins and casein in a mixed colloidal system, subjected to moderate heating (65°C for 30 min) prior to renneting, on the gelling properties of the system. Increasing levels of added whey protein, in the concentration range of 0.225 to 1.35% of added protein, led to a concomitant progressive increase in the equilibrium shear storage modulus, G' (recorded after 10,800 s), in the order ß-LG B > ß-LG A and ß-LG A-B, as the general expected consequence of the setup of denser casein gel networks. The preferential effect of ß-LG B over ß-LG A on the mechanical strength of the gels may be due to the formation of cross-links and aggregates involving whey proteins and rennet hydrolysis products or an increase in the size of the casein micelle caused by the grafting of ß-LG B to its surface, or both. The results of free-zone capillary electrophoresis were consistent with the notion that ß-LG B (and not ß-LG A) binds to the casein micelle under an optimal stoichiometry of 1:0.045 (mg/mg), even in the absence of heat treatment. The liquid-like character of the gel networks formed, tan , was a parameter sensitive to the level of addition of ß-LG A in particular. At low concentrations (up to 0.45%) of ß-LG A, tan increased by almost twice as much, which was interpreted as a result of the increase in the loss modulus, G'', of the sol fraction because of the presence of unbound ß-LG A. At greater incremental concentrations of ß-LG (>0.45%), the formation of smaller whey protein aggregates confined to the sol fraction may have led to a progressive decrease in tan . The critical gel time, t_gel, was also affected by the concentration of added whey protein and described 3 zones of behavior, irrespective of the type of whey protein variant. The critical gel time was slightly shorter for ß-LG B than for ß-LG A at 0.45% of added whey protein, but this difference became larger at 0.67%. Even when only ß-LG B was found to associate with casein prior to renneting, both ß-LG A and ß-LG B, either alone or mixed, had a profound influence on the mechanical strength and coagulation kinetics of the rennet-induced casein gels. This knowledge is expected to be useful to exert better control and optimize processing conditions during the manufacturing of cheese and cheese analogs.

Key Words: ß-lactoglobulin whey protein variant • rennet-induced gelation • capillary electrophoresis • rheology