2009_Book_FoodChemistry

8.12.3 Sorbic Acid
8.12 Antimicrobial Agents 451
The antimycotic effect of straight chain carboxylic
acids has long been known. In particular
the unsaturated acids, for example crotonic acid
and its homologues, are very active. Sorbic acid
(2-trans, 4-trans-hexadienoic acid; pK = 4.76)
has the advantage that it is odorless and tasteless
at the levels of use (0.3% or less). The acid is
obtained by several syntheses:
• From parasorbic acid [(S)-2-hexen-5-olide);
cf. Reaction 8.27]. The acid is present in
berries of the mountain ash tree (Sorbus
aucuparia).
Fig. 8.12. Growth inhibition of Aspergillus niger by
benzoic acid (•), p-hydroxybenzoic acid propyl ester
(◦) and sorbic acid ()
• From ethanal:
(8.27)
Unlike benzoic acid, the esters can be used over
a wide pH range since their activity is almost
independent of pH (cf. Fig. 8.12). As additives,
they are applied at 0.3–0.06% as aqueous alkali
solutions or as ethanol or propylene glycol solutions
in fillings for baked goods, fruit juices,
marmalades, syrups, preserves, olives and pickled
sour vegetables.
(8.28)
• From crotonaldehyde obtained from ethanal
(cf. Reaction 8.29).
(8.29)
The third synthesis is the most important.