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: xyang5@ncsu.edu.
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