(3) Certain substances can retard the rate of the hardening which takes
place during the staling of bread. These materials are emulsifying agents which are
used as "freshness preservers."
1-20. SURFACE SLIME
a. Common on Food Products with High Moisture Content. Surface slime is
found on the surfaces of (or within) food products which have a high moisture content.
Slime can be found on meat products, fresh fruits and vegetables, waterfoods, and
various other foods. The surface of product will be "slippery" to the touch. The
veterinary food inspection specialist should be aware that early stages of slime
formation may not be readily recognizable. It may be frequently mistaken for a film of
surface fat. As a general rule, however, an off-odor is detected before the "slime" can
be physically detected.
b. Cause of Surface Slime. Surface slime is caused by the growth of bacteria,
mainly of the lactic acid type which includes Lactobacillus, Leuconostoc, Streptococcus,
and Pseudomonas. The slime is actually billions of bacteria on the surface of the
product and is not a metabolic product of the microorganisms. All of the causative
bacteria are able to grow at refrigerator temperatures on the moist surfaces of the food
c. Visible Slime. The time interval for the onset of visible slime is dependent
upon the amount of initial surface contamination, the holding temperatures of the food,
and the amount of surface moisture.
1-21. SUMMARY OF DETERIORATION
The major modes of deterioration in various products are summarized in figures
1-1 and 1-2. Also listed in this figure is a list of critical environmental factors that play
an important role in the deterioration of food items.
1-22. OTHER CONDITIONS
There are several conditions in food products that may be confused with
a. Struvite Crystals. Small crystals of a harmless chemical substance,
magnesium ammonium phosphate (also referred to as struvite), often gradually form in
fish and shellfish packs. The constituents of these crystals are necessary for normal
health. They cause no harm if swallowed. However, the crystals are often mistaken for
glass and thus are undesirable. Their formation may be reduced or eliminated by the
addition of certain chemicals to waterfoods prior to canning. Struvite crystals are
commonly seen in cans of tuna and salmon.