2009_Book_FoodChemistry

450 8 Food Additives
(pK a = 4.19) is predominantly active. As in the
case of sorbic acid and propionic acid, a certain
activity is also attributed to the anion.
Benzoic acid usually occurs in nature as a glycoside
(in cranberry, bilberry, plum and cinnamon
trees and cloves). Its activity is primarily against
yeasts and molds, less so against bacteria. Figures
8.10 and 8.12 show the pH-dependent activity
of the acid against Escherichia coli, Staphylococcus
aureus and Aspergillus niger.
The LD 50 (rats; orally) is 1.7–3.7g/kg body
weight; the LD 100 (guinea pig, cat, dog, rabbit;
orally) is 1.4–2 g/kg. A daily intake of <0.5g
Na-benzoate is tolerable for humans. No dangerous
accumulation of the acid occurs in the
body even at a dosage of as much as 4 g/day.
It is eliminated by excretion in the urine as
hippuric acid while, at higher levels of intake, the
glucuronic acid derivative is also excreted.
Benzoic acid (0.05–0.1%) is often used in
combination with other preservatives and, on
the basis of its higher activity at acidic pH’s,
it is used for preservation of sour food (pH
4–4.5 or lower), beverages with carbon dioxide,
fruit salads, marmalades, jellies, fish preserves,
margarine, paste (pâté) fillings and pickled sour
vegetables. A change in aroma, occurring mostly
in fruit products, may result as a consequence of
benzoic acid esterification.
8.12.2 PHB-Esters
The alkyl esters of p-hydroxybenzoic acid (PHB;
parabens) are quite stable. Their solubility in water
decreases with increasing alkyl chain length
(methyl → butyl). The esters are mostly soluble
in 5% NaOH.
The esters are primarily antifungal agents and are
also active against yeasts but less so against bacteria,
especially those which are gram-negative.
The activity rises with increasing alkyl chain
length (Fig. 8.11). Nevertheless, lower members
of the homologous series are preferred because
of better solubility.
The LD 50 (mice; orally) is >8 g/kg body weight.
In a feeding experiment over 96 weeks using
2% PHB-ester, no weight decrease was observed,
while a slight decrease was found at the 8% level.
In humans, the compounds are excreted in urine
as p-hydroxybenzoic acid or its glycine or glucuronic
acid conjugates.
Fig. 8.10. The effect of benzoic acid on Escherichia coli
(◦ bacteriostatic. • bactericidal activity) and Staphylococcus
aureus (△ bacteriostatic and bactericidal activity)
Fig. 8.11. Inhibition of Salmonella typhosa (•), Aspergillus
niger (△), Staphylococcus aureus (◦), and
Saccharomyces cerevisiae ()byPHB-esters