EFFECTS OF PH AND NEUTRAL SALTS ON THE FORMATION AND QUALITY OF THERMAL AGGREGATES OF OVALBUMIN - STUDY ON THERMAL AGGREGATION AND DENATURATION

The effect of NaCl and CaCl2 on the aggregation and denaturation temperature of ovalbumin was examined in the pH interval 3‐11. It was found that ovalbumin had maximal thermal stability between pH values of 6‐10. NaCl did not affect the denaturation temperature, while a small decrease was observed with CaCl2 even at the low concentration range investigated. Both salts extended the pH interval of thermal aggregation, but at the alkaline side of the isoelectric point CaCk suppressed the aggregation temperature more than did NaCl. The aggregation properties of S‐ovalbumin were also investigated and found to be similar to those of ovalbumin, although aggregation occurred at a higher temperature level. The quality of the aggregates was described by their dry matter content. Aggregates appeared as transparent gels, opaque gels, gel‐like precipitates and precipitates. The addition of NaCl gave predominantly gel aggregates at the alkaline side of the isoelectric point, while precipitates dominated when CaCl2 was added. Gelling is an intermediate phenomenon which occurs between the two extremes of precipitating and non‐aggregating conditions. Special conditions, in terms of electrostatic repulsion between the protein molecules, are required for gelling, which could be achieved by manipulating with pH, type of salt, salt concentration or added detergent. The difference between aggregation and denaturation temperature correlated with the dry matter content of the aggregates formed. When aggregation temperature was well below denaturation temperature, the resulting aggregates had a high dry matter content (precipitates). Gelling, on the other hand, was observed at an aggregation temperature equal to or above the denaturation temperature. Copyright © 1979 John Wiley & Sons, Ltd