Comparative study of bovine and ovine caseinate aggregation processes: Calcium-induced aggregation and acid aggregation

MARÍA EUGENIA HIDALGO; MANUEL A. MANCILLA CANALES; CÁSSIA R. NESPOLO; ANSELMO D. REGGIARDO; ESTELA M. ALVAREZ; JORGE R. WAGNER; PATRICIA RISSO

Protein Aggregation

Nova Publishers

Lugar: Hauppauge, NY; Año: 2011; p. 199 - 222

The solubility of colloidal particles of bovine and ovine caseinate in the presence ofcalcium was studied by analyzing the colloidal particle size and the protein compositionof casein colloidal aggregates remaining in suspension. A comparison between thebehaviour observed for bovine and ovine caseinate was carried out. A two-step saltingoutprocess, due to progressive Ca2+ binding to at least different two kinds of sites wasobserved for both caseinates. The precipitation curves were fitted and the affinityconstants and binding site numbers were estimated with an equation based on the conceptof Wyman’s linked functions. Ovine caseinate colloidal aggregates formed in thepresence of calcium turned out to be less stable and quite bigger than the bovine ones.The binding of calcium to protein residues with some particular characteristics modifiesprocess at low caseinate concentration and an acid-induced gelation process at highprotein concentration triggered by the hydrolysis of glucono-δ-lactone were also studied.The effects that variables such as temperature, protein concentration and GDL amountexerted on these processes were analyzed using spectroscopic-based methods andmeasuring the rheological properties of systems. The time required to initiate particlesaggregation decreased in parallel with an increment of temperature, amount of GDLadded and caseinate concentration. An increase in caseinate concentration or a reductionof temperature produced gels with a substantial rise in the storage modulus.Modifications of GDL/caseinate ratio did not resulted in significant changes in therheological parameters determined. The kinetic of the aggregation and compactnessdegree of ovine caseinate aggregates formed at the end of the acidification process weredifferent from those of bovine source. Acid-induced aggregation and gelation processeswere also investigated in the presence of calcium concentrations where no precipitationoccurs. The addition of calcium affects the kinetic of both processes and the final state ofthe aggregates or gels obtained. Consequently, the degree of compactness and averagesize of the aggregates and rheological properties of gels produced at the end of theacidification process depend on the calcium concentration added.