e. Freeze Dehydration. Freeze dehydration is a method used to preserve fish
squares and shrimp. The moisture content is reduced to approximately 2%. The
product is then placed in cans, nitrogen is used to remove the oxygen, and then the can
is sealed. This method provides the longest safe storage time. However, freeze
dehydration is expensive and is not used as often as other methods.
f. Canning. Canning is another method used for food preservation. Canning
destroys spoilage bacteria through commercial sterilization and allows long-term
storage without refrigeration. Canned salmon, tuna, and sardines are the three items
procured for troop issue. However, numerous canned waterfoods may be found in the
retail sales stores.
g. Vacuum Pack. Vacuum packing is a method that has become more
common in waterfood preservation, especially in regard to frozen halibut and salmon
steaks. The product is frozen, cut to a specified thickness, weighed, and then placed in
a heavy plastic pouch. A vacuum is used to remove the oxygen and the pouch is heat
sealed. The packaged product then passes through a steam chamber to shrink the
pouch to the product. This eliminates the need to determine the amount of glaze and
allows the inspector to examine the product for visual deteriorative conditions (for
example, oxidation and freezer burn).
a. General. Deteriorative conditions are the result of bacteriological changes or
chemical changes associated with storage. The most common are described below.
b. Bacteriological Conditions.
(1) Microbial spoilage. Microbial spoilage is the major cause of deterioration
of waterfoods. Fish are high in both water and protein, both necessary nutrients for the
growth of the bacterial organisms that cause spoilage. The bacteria associated with
fish are predominantly psychrophilic (cold-loving) and grow within temperatures of 32o-
70o F. Psychrophilic bacterial contamination produces color changes (from a red to a
slight green color), slime formation, and off odors.
(2) Honeycombing. Honeycombing is the formation of small pitted holes
within the flesh and is the result of gas forming bacteria. The digestive enzymes, after
destroying most of the digestive tract, penetrate the flesh adjacent to the poke. This
condition is accompanied by a sharp taste and odor. Honeycombing is sometimes
found in canned tuna and salmon. Gas is formed in the flesh by gas-producing bacteria
present prior to canning. The inspector will see small pitted holes like pinholes in the
surface flesh. A sharp, acid taste can be detected during a sensory examination.
Proper sanitation and refrigeration can control microbial spoilage and retard its
processes. Honeycombing may also be caused by refreezing; however, this will not
affect the taste or odor.