Tímarit Verkfræðingafélags Íslands - 01.12.1967, Blaðsíða 290

288
TlMARIT VPl 1967
very efficient nor frequently very sanitary. The
widespread usefulness of such methods is based
upon the fact that the removal of water from
biological tissues causes chemieal changes to
occur that reduce enzyme action and prevent
microbial decomposition. Dehydration is thus
the first and perhaps the most important factor
in the preservation of fish.
Apart from water, which makes up almost 80
percent by weight of the raw material, fish also
contain oils and other fat-related compounds.
These are present in much smaller quantities
than the water but are of great importance.
Under the proper conditions, in fact, some of
these highly reactive and diverse components,
grouped together under the category of lipids,
can rapidly become rancid and thus lead to the
formation of odor-bearing compounds, which are
not only considered by many to be extremely
offensive, but may also, by side reactions, result
in a reduction in the nutritive value of the
finished product. Lipids must, therefore, be re-
moved as exhaustively as possible if a stable,
bland, and safe end-product is to be prepared.
One of the methods by which both water and
lipids can be removed from the raw material is
by extracting these components, together with
odor-bearing compounds, by a suitable solvent.
Solvent extraction was, therefore, selected as
the processing method for the preparation of
FPC.
2. Extraction of water and lipids in FPC
production. — The removal of water by solvent
extraction from the raw fish presents no parti-
cular problems; the extraction of lipids how-
ever, presents certain unique processing
problems. These are due to the almost contra-
dictory requirements of exhaustive removal of
lipids, on the one hand, and the preservation,
on the other, of the nutritive value of the
proteins to which certain lipids are firmly
attached. The extraction of lipids from fish is
further complicated by the following facts:
a. Lipid-protein and Upid-carbohydrate com-
plexes in the tissue are often insoluble in fat
solvents.
b. Certain lipids are soluble to only a limited
extent in the usual fat solvents.
c. Some conventional fat solvents are effi-
cient solvents for certain nonlipid constituents
of the tissue.
d. The original wet tissue cannot be effi-
ciently extracted by many solvents that are
efficient only when used with dry tissue; when
such solvents are used, the wet tissue must
therefore be dried first.
In general, the number of different solvents
used in the commercial extraction of lipids in
other food precessing operations is very limited.
Also, in ahnost all food processes presently used,
single solvents are employed for the extraction
of lipids, because of the need to minimize solvent-
recovery problems.
3. Choice of solvent. — Examination of exist-
ing solvent systems, of the scientific and political
problems facing the FPC concept, and of the
overall program goals, led to the formulation of
basic guidelines.
A single solvent should be used, to simplify
control of the process, to ensure the safety of
process and product and to assure the greatest
degree of process simphcity.
The solvent should have bactericidal properties
and arrest the activities of enzymes. It must
also be capable of dissolving water, fats, and fat-
like substances, and must be of the lowest possi-
ble order of toxicity. It should not impart a
permanent odor or taste to the extracted proteins.
The solvent should be inert towards proteins,
amino acids, and the usual materials of plant
construction, and should have a low boiling point.
It should present no undue fire or explosion
hazards and be generally safe to handle, but
should also be inexpensive, easily available and
obtainable in very pure form. Finally, there
should be no undue difficulties in the recovery
of the pure solvent.
Although no single solvent is presently known
that can meet the above criteria totally, two
common solvents appeared to be most suitable:
isopropyl and ethyl alcohol. Isoprophyl alcohol,
chosen in preference to ethyl alcohol for practi-
cal reasons has, so far, given exceUent results
in the extraction of lean fish such as hake and
promises to be equaUy suitable for the processing
of fatty fish.
4. Choice of processing equipment. — The
guidehnes for the selection of process equipment
include first and foremost provision for complete
process sanitation. Eqmpment to be selected must
be easily disassembled, cleaned, and sterilized and
provision must be made for a completely closed
process flow. Materials of construction must be
corrosion resistant and capable of withstanding
sterihzation temperatures. A further important
requirement is that, as far as possible, only
readily available conventional equipment should
be used.