(Yamamoto et al, 1984a). Since acetic acid does not
generally have a strong preserving action, it is often
combined with physical methods of preservation, such as
pasteurization, or with salt and/or the more powerful
preservatives sorbic acid or benzoic acid.
Besides its preservative action, acetic acid is very
important as a flavoring; indeed, in many foods its primary
function is a flavoring and its preservative function is of
secondary importance. The action of acetic acid on protein
may also have an influence on flavor. At low concentrations,
acetic acid causes partial protein hydrolysis, especially in
animal tissues, which may lead to the production of
agreeably flavored cleavage products. This effect is
important chiefly in the production of fish marinades.
Whereas common salt tends to make fish meat firmer,
vinegar has a tenderizing effect.
b. Salt
Salt (NaCl; MW 58.44) is one of the most important
adjuncts in food preservation for centuries. It is employed
on large scale, especially for meat, fish and vegetables. Salt
has retained its importance in food preservation to the
present day, although it is now used less as a preservative in
its own right than in combination with other preservatives
and preservation methods. Salt is obtained from rock salt
deposits and seawater. The rock salt obtained by mining is
not sufficiently pure for use in food. To produce salt for
culinary purposes, rock salt is dissolved underground in
water and, after appropriate purification, is dried by
evaporation in large pans. To obtain sea salt, sea water is
allowed to evaporate in shallow tanks in hot countries by
solar heat, thus causing the individual salts contained in
seawater to crystallize out in succession (Kaufmann, 1960).
Salt lowers the water activity of a system and thus
renders conditions less favorable to microbial life. Its mode
of action is therefore comparable with that of drying; hence
the term “chemical drying” to describe the used of salt.
However, since the water activity value of saturated salt
solution is only about 0.75 and a number of microorganism
varieties are able to grow even below this limit, it is
impossible to protect a food stuff reliably from all microbial
attack by using salt alone, unless the flavor becomes
completely unacceptable (Kushner 1971). The foods to be
preserved can be immersed in solutions containing greater
or lesser amounts of salt (brines). Alternatively, dry salt can
be added to food. The resulting osmotic removal of water
from the food reduces the water activity to a level according
to the quantity of salt added. Table 4 shows this relationship.
According to their salt tolerance, microorganisms are
defined as slightly halophilic (salt-tolerant), moderately
halophilic or extremely halophilic. Halophilic bacteria grow
best in the presence of some 1-5% salt. Moderately
halophilic microorganisms tolerate 5-20% salt and
extremely halophilic strains up to 30%. The effect of salt on
lowering water activity does not in itself adequately explain
its antimicrobial action. Certain clostridia strains, for
example, grow in the presence of salt only if the water
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