c. Limiting Factor for Dehydrated Foods. Nonenzymatic browning may occur
in dehydrated foods (such as meat, eggs, and some fruits and vegetables) after storage
for a time. This browning reaction makes dehydrated items objectionable, so much so
that this otherwise promising method of food preservation is extremely limited in its
d. Problem in Long-Term Storage. Nonenzymatic browning is most
troublesome in foods, even canned sterilized foods stored for long periods of time at
relatively high temperatures. Consequently, food deterioration due to nonenzymatic
browning is a great problem in military and survival rations, which are often stored at
relatively high temperatures. Although, in a few instances, the browning reaction can be
delayed by certain food ingredients, the best way to diminish nonenzymatic browning is
proper food processing and storage conditions.
Staling is a rather general term applied to a variety of chemical deteriorative
changes. Staling is usually manifested as adverse alterations of taste, odor, and texture
in prepared foods which are not promptly eaten. The changes may lead to rejection of
stale food even though it may not be altered nutritionally.
a. Control Techniques. All of the changes are related to the fact that foods are
composed of many substances that are chemically altered by heating. Many of the new
compounds formed by heating are unstable and react in time with oxygen from the air or
with other chemical compounds present in the food. To prevent such changes, many
commercially processed foods are heated and stored in the absence of oxygen, for
example, canned foods. Another way of excluding most of the oxygen in frozen or
refrigerated foods is to have the food covered with sauce or some other liquid and
packaged in a container with little residual air.
b. Bread as an Example. The staling of bread and related products is familiar
to everyone. Furthermore, no better example of food can be found to illustrate the
changes in both flavor and texture so typical of the staling process.
(1) Desirable flavors in bread and many other foods result from crust
formation. For the purpose, the surface of the food, particularly during baking, is
subjected to temperature above the boiling point of water. The heat causes intensified
breakdown of food constituents.
(2) Upon standing, even in packages which allow no water loss, bread will
degenerate in flavor and become harder and crumbly in texture. This latter change is
not due to drying out but to rearrangements of the molecules of water, starch, and
protein in the bread itself.