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Whey proteins dominate the air-water interface in protein mixtures.

Protein foams are an integral component of many foods. They play an important role in determining the quality of a product. Egg white protein (EWP) has been historically used as a foaming agent because of its ability to form foams with high volume--overrun--and stability.

Whey protein isolate (WPI) produces foams similar to EWP foams in terms of overrun. WPI could potentially replace EWP in different products. But simply replacing EWP with WPI is not practical for some baking applications. The precise reason for the lower functionality of WPI in baking applications has not been known.

Scientists at North Carolina State University compared the foaming properties of WPI, EWP and their blends in different model and food systems. Their work shows that foam functionality using blends of WPI and EWP is not additive, and suggests that whey proteins dominate the air-water interface in mixed systems.

The researchers investigated the physical properties of foams--overrun, yield stress, volume, surface tension and dilatational elasticity at air-water interfaces. The progressive substitution of WPI with EWP did not cause major changes in foam overrun. In contrast, adding WPI caused decreases in foam stability (drainage time) and yield stress. Changes in surface tension showed that the lowest level of WPI substitution--75% EWP and 25% WPI--was enough to cause the temporal pattern of surface tension decrease to be similar to that found when using all WPI. This suggests that whey proteins dominate the interface. However, changes in dilatational elasticity modulus were more suggestive of a mixed interface.

In one instance, the volume of angel food cake decreased with increasing proportions of WPI. The foam structure showed a marked increase in bubble size before a major change occurred in cake volume. It appears that whey proteins dominate the air-water interface in protein mixtures. While this did not alter overrun, it caused a decrease in foam stability, yield stress and angel food cake quality.

Further information. Xin Yang, North Carolina State University, Department of Food Science, Schaub Hall, Room 236-F, Raleigh, NC 27695; phone: 919-513-2244; fax: 919-515-4694; email:
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Publication:Emerging Food R&D Report
Date:Jan 1, 2008
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