Bread tends to stale—i.e., obtain a harder and shorter texture—during
storage at room temperature. Keeping the bread in a refrigerator
enhances staling rate, but storage in a freezer greatly reduces staling.
How is this explained?
The physical stability of a certain oil-in-water emulsion is observed to
depend greatly on temperature. At 40 8 C it remains stable, after
cooling to 25 8 C also, but after cooling to 10 8 C and then warming to
258 C small clumps are formed; stirring greatly enhances clump
formation. What are the mechanisms involved and how is the
dependence on temperature history explained?
Another emulsion shows undesirable creaming. To reduce creaming
rate a small amount of a thickener, i.e., a polysaccharide, is added.
However, it increases the creaming rate. How?
Food technologists have to design and improve processes to make
foods having specific qualities in an efficient way. Examples of problems are
Many foods can spoil by enzyme action, and the enzymes involved
should thus be inactivated, which is generally achieved by heat
denaturation. For several enzymes the dependence of the extent of
inactivation on heating time and temperature is simple, but for
others it is intricate. Understanding of the effects involved is needed
to optimize processing: there must be sufficient inactivation of the
enzymes without causing undesirable heat damage.
It is often needed to make liquid foods with specific rheological
properties, such as a given viscosity or yield stress, for instance to
ensure physical stability or a desirable eating quality. This can be
achieved in several ways, by adding polysaccharides, or proteins, or
small particles. Moreover, processing can greatly affect the result. A
detailed understanding of the mechanisms involved and of the
influence of process variables is needed to optimize formulation and
processing.
Similar remarks can be made about the manufacture of dispersions of
given properties, such as particle size and stability. This greatly
depends on the type of dispersion (suspension, emulsion, or foam)
and on the specific properties desired.
How can denaturation and loss of solubility of proteins during
industrial isolation be prevented? This is of great importance for the
retention of the protein’s functional properties and for the economy
of the process.
How can one manufacture or modify a powdered food, e.g., spray-
dried milk or dry soup, in such a manner that it is readily
dispersable in cold water?