Kristinsson, 2005 – Acid and Alkali Unfolding and Refolding Strategies to Improve the Foaming Properties of Egg White Proteins

Eggs and egg whites (albumen) are an important commodity in the US and are used in a variety of food products due to the versatile nature of the various proteins found in the albumen. Variable foaming performance of egg albumen has always posed a problem in the food industry. Several different methods have been proposed in the past to improve foaming properties of egg whites, most focusing on heat denaturing the proteins. However, if heat treatment is too extensive, protein concentration too high or the protein is at a pH and ionic strength that favors aggregation, coagulation may occur and foaming properties are adversely affected. One way to increase the foaming functionality of egg proteins would be to induce a conformational change without heat that leads to a protein of increased hydrophobic and flexible nature, i.e. partially denature the protein. Employing different “extreme” pH treatments is an alternative means to heat, to induce a positive conformational change in the egg albumen proteins to increase their foaming properties. To the best of the investigators knowledge it had not been previously studied how controlled acid and alkali denaturation followed by pH readjustment to renaturing conditions affected the foaming properties or conformation of the albumen proteins, collectively or individually. This was the overall goal of the project described in this final report. Previous studies by the investigator on fish and land animal muscle proteins had demonstrated that certain extreme pH treatments where proteins are subjected to a very low or high pH and then readjusted to different pH values in the native pH range of the proteins, led to dramatic improvements in thefunctional properties of these proteins. We wanted to investigate how a large variety of pH treatments would (a) affect the foaming properties of egg albumen proteins, (b) structural and conformational properties of egg albumen proteins, and (c) the function of selected pH treated proteins in actual food products.