Another major cause of food deterioration is chemical reactions. Chemical
reactions in foods are sometimes very complex and subtle. Chemical reactions,
excluding the action of enzymes, are responsible for such diverse deteriorative changes
as oxidation, color changes, reactions between a food container and its contents, and
the coagulation of proteins.
a. Temperature. We know the rate of deterioration will be significantly
influenced by temperature. We can borrow a rule of chemistry (van't Hoff's rule) to
estimate the rate at which the deterioration change will take place. In essence, the rule
states that for every 18F (10C) increase in temperature, the rate of a chemical
reaction doubles. This rule will suffice for our purposes when we apply it to chemical
reactions occurring in foods. Using this general rule, we can say that for every 18F
(10C) increase in storage temperature of a food, the shelf life of the food will be
reduced by one half, for the deteriorative chemical reaction rate will have doubled.
b. Other Causes of Chemical Reactions. There are many reactions which can
lead to the deterioration of food quality or impairment of food safety. Each reaction can
involve different reactants or substrates, depending on the specific food and the
particular conditions for processing or storage of that food.
Physical changes may not cause a food to become spoiled, but they do cause
deteriorative changes which may cause the food item to be unsuitable for intended use.
Some of the physical changes which cause deteriorative changes in foods are as
a. Low Temperature.
(1) Freezing and undesirable changes. Freezing of many foods will cause
undesirable changes, such as the destruction of emulsions and texture. Emulsified
products, such as salad dressing and mustard, contain a fat/oil and water mixture which
does not combine without special processing or additives. If these types of products are
frozen, the emulsion will be destroyed and the fat and water will separate into distinct
layers. Fruits and vegetables that are allowed to freeze and then thaw will have their
texture disrupted. Skins will crack, leaving the food susceptible to attack by
microorganisms. The texture of canned fruits and vegetables becomes softened and
mushy due to uncontrolled freezing.