2009_Book_FoodChemistry

452 8 Food Additives
The microbial activity of sorbic acid is primarily
against fungi and yeasts, less so against bacteria.
The activity is pH dependent (Fig. 8.12). Its utilization
is possible up to pH 6.5, the proportion of
undissociated acid being still 1.8%.
The LD 50 (rats) of sorbic acid is ca. 10 g/kg body
weight. Feeding experiments with rats for more
than 90 days, with 1–8% sorbic acid in the diet,
had no effect, while only 60% of the animals survive
an 8% level of benzoic acid.
Sorbic acid is degraded biochemically like a fatty
acid, i. e. by a β-oxidation mechanism. A small
portion of the acid is degraded by ω-oxidation,
yielding trans, trans-muconic acid (cf. Reaction
8.30).
(8.30)
Some microorganisms, such as Penicillium
roqueforti, have the ability to decarboxylate sorbic
acid and thus convert it into 1,3-pentadiene,
which has no antimicrobial activity and in
addition may contribute to an off-flavor in
cheeses:
(8.31)
Sorbic acid or its salts are effective antifungal
agents in baked products, cheeses, beverages
(fruit juices, wines), marmalades, jellies, dried
fruits and in margarine.
8.12.5 Acetic Acid
The preserving activity of vinegar (cf. 22.3) has
been known from ancient times. The acid has
a two-fold importance: as a preservative and as
a seasoning agent. It is more active against yeasts
and bacteria than against molds. It is used as the
free acid, Na- and Ca-salts, or as Na-diacetate
(CH 3 COOH·CH 3 COONa·1/2H 2 O), in ketchup,
mayonnaise, acid-pickled vegetables, bread and
other baked products.
8.12.6 SO 2 and Sulfite
The activity of these preserving agents covers
yeasts, molds and bacteria. The activity increases
with decreasing pH and is mostly derived from
undissociated sulfurous acid, which predominates
at a pH < 3.
Toxicity is negligible at the levels usually
applied. Possible mutagenic activity is under
investigation. Excretion in the urine occurs as
sulfate.
Sulfite reacts with a series of food constituents,
e. g., proteins with cleavage of disulfide bonds
(cf. 1.4.4.4), with various cofactors like NAD ⊕ ,
folic acid, pyridoxal, and thiamine (cf. 6.3.1.3)
and with ubiquinone:
8.12.4 Propionic Acid
Propionic acid is found in nature where propionic
acid fermetnation occurs, e. g., in Emmental
cheese, in which it is present up to 1%.
Its antimicrobial activity is mostly against molds,
less so against bacteria. Propionic acid has practically
no effect against yeast. Its activity is pH dependent.
It is recommended and used up to pH 5
and only occasionally up to pH 6.
Propionic acid is practically nontoxic. It is used
as an additive in baked products for inhibition of
molds, and to prevent ropiness caused by the action
of Bacillus mesentericus. It is added to flour
at 0.1–0.2% as its Ca-salt and is used in cheese
manufacturing by dipping the cheese into an 8%
solution of the acid.
(8.32)
The pyrimidines in nucleic acids can also react,
e. g., cytosine and uracil (cf. Formula 8.33). Anthocyanins
are bleached (cf 18.1.2.5.3).
(8.33)
SO 2 is used in the production of dehydrated
fruits and vegetables, fruit juices, syrups, con-