Title:
Preparation of culinary solid foams derived from proteins. Study of their
composition and stability.
Student: María Fabián Alfonso
Date: January 2014
Supervisor/s: Dra. Carme González Azón
Departament of Chemical Engineering
Dr. Esther Santamaría Hernández
Departament of Chemical Engineering
Foams are colloidal systems formed by gas bubbles surrounded by thin films of liquid. They
are thermodynamically unstable and tend to collapse. However, foams can have a long
persistence due to the presence of surfactants.
In gastronomy field, foams are usually used, mainly those made of egg whites.
The existence of these foams is due to its high protein content. Proteins act as a surfactant
and reduce the surface tension between bubbles and liquid because they are amphiphilic.
Therefore, surfactants allow the foam formation. Moreover, they stabilize the films against
rupture.
Egg-white foams produce certain products that are recognized as emblematic forms in
culinary art. Meringues were chosen as a subject of study because their preparation is relatively
simple and represents a model system to study the behavior off egg whites froths. This
confection is generally defined as a mixture of beaten egg whites and sugar.
The stability of egg white foams based on different factors such as protein: water
relationship, egg white types (fresh, pasteurized, lyophilized and powdered albumin), amount of
sugar and types (white and icing sugar), temperature and agitation rate.
This study was based on the stability measurements of foams formed by changing the
variables proposed above to analyze how their behavior was modified and to discover what kind
of foam is more stable. This would be helpful for bakers and chefs that want to work with this
type of foams. The stability values were related with bubble diameter and foams air fraction
measurements.
Protein percentage and sugar amount had a positive influence on foams density and
stability but a negative influence on air phase fraction and bubble diameter values. Hence,
foams were more stable and dense but their bubbles were smaller and air phase fraction was
lower against higher amount of sugar and proteins. Consequently, proteins and sugar improved
foam stability and formed foams with smaller bubbles, so with more density and low air fraction.
Some proteins on pasteurized and liofilized albumen are denaturalized due to a thermal pretreatment, this phenomenon provide a lower viscosity and cause a quickly liquid drainage,
resulting less stable foams, while other types of egg white formed foams that destabilized
slowly.
Temperature had a double effect. Albumen foamed more easily and attains greater volume
at high room temperature because the protein denaturalization was easier than at low
temperature. However, at low room temperature, foams increased their viscosity and retarded
hydrodynamic drainage.
Agitation rate and types of sugar were not important factors to take in account when
obtaining foams according to the studied range because the result of stability would be similar,
but was better using icing sugar to improve the meringue texture.
Keywords: foam, colloidal system, foam stability, gastronomy.