Gelation by phase separation in a whey protein system: in-situ kinetics ofaggregation

The aggregation and gelation properties of beta-lactoglobulin (BLG), a glob ular protein from milk, was studied in aqueous ethanol solutions at room te mperature. The phase state diagrams as a function of pH and ethanol concent ration showed that a gel structure appeared after a period ranging from 1 m in to 1 week, depending on the physico-chemical conditions. The in-situ kin etics of aggregation were followed by several methods in order to obtain a better understanding of the building of aggregates by the addition of ethan ol. It was shown that the aggregation kinetics highly depended upon the pH, the process being fastest at pH 7. Viscoelasticity and infrared measuremen ts indicated that alcohol-induced gelation would proceed via a two-step mec hanism: small aggregates loosely connected between them were first built up ; a real network took place in a second step. The coarse and irregular stru ctures formed in aqueous ethanol gels revealed by confocal laser scanning m icroscopy could be analysed in terms of a phase separation. This observatio n was supported by a syneresis phenomenon visible in the final gel state. B LG in water-ethanol solution would undergo either an inhibition of the demi xing by gelation or a binary phase separation accompanied by an irreversibl e gelation transition. (C) 2000 Elsevier Science B.V. All rights reserved.