EFFECT OF PH AND CATIONS ON THE THERMALLY-INDUCED GELATION OF OVALBUMIN

The gelation of ovalbumin in the presence of salts containing Ca+2 and Mg+2 at various pH values was investigated. Characteristics of the ge ls produced were evaluated using penetration measurements on an Ottawa Texture Measuring System as well as dynamic rheology on a Bohlin VOR rheometer. Gel properties were related to cation binding (equilibrium dialysis) and to changes in protein structure (differential scanning c alorimetry). Cation binding generally increased with increasing salt c oncentration, and Mg+2 bound to a greater extent than Ca+2 at the high er levels studied. The impact of this binding on gel structure was dep endent on pH and the technique used to evaluate structure. At pH 5 pro teins tended to coagulate regardless of the type or amount of salt. At pH 7, the highest rigidity values from penetration measurements were obtained at salt levels of 0.005 M. At pH 9, the salt concentration fo r maximum rigidity varied with the salt, while the storage moduli (G') from dynamic rheology were highest at the highest salt concentration used. Based on rigidity data, the inclusion of 0.005 M MgSo(4) would g ive a product with the greatest rigidity over a wide pH range.