Moisture-induced aggregation of whey proteins in a protein/buffer model system.

Moisture-induced protein aggregation in a dry or intermediate-moisture food matrix can contribute to the loss of product acceptability. The present study evaluated the molecular mechanisms and controlling factors for moisture-induced whey protein aggregation in a premixed protein/buffer model system. Insoluble aggregates rapidly formed during the first 3 days of storage at 35 degrees C with a slower rate afterward. Evaluation of the insoluble aggregates by solubility tests in solutions containing SDS/urea/guanidine HCl/dithiothreitol and gel electrophoresis showed that the formation of intermolecular disulfide bonds was the main mechanism for protein aggregation, and all major whey proteins were involved in the formation of insoluble aggregates. Effects of various factors on aggregation were also investigated, including moisture content, medium pH, and the addition of NaCl. The dependence of aggregation on moisture content was bell-shaped, and the maximal extent of aggregation was achieved at a moisture content of around 70-80% on a dry weight basis.