Produce Degradation Pathways and Prevention

Mechanisms of Food Additives, Treatments, and Preservation Technology 331

Sorbic acid has properties similar to those of benzoic acid. It is used as acid or
salts of sodium, potassium, or calcium at concentrations that range from 500 to
2,000 mg/kg. It is more effective against yeasts and molds than against bacteria. Its
inhibitory effect decreases with dissociation, but its pK value is higher than that of
benzoic acid. Sorbic acid can be used in neutral pH solutions. The solubility of
sorbic acid in water is also low (1.6 g/L at 20°C, 39 g/L at 100°C) and sorbic acid
has technological consequences similar to those of benzoic acid^ (Bibek, 1996).
Parabens are alkyl esters of 4-hydroxybenzoic acid. They are used as methyl, ethyl,
propyl, or butyl paraben. Parabens are broad-spectrum preservatives effective against
bacteria, yeasts, and molds. They are used at concentrations from 100 to 1000 mg/kg
for various acidic and low-acid food products. The antimicrobial effect of individual
parabens increases with the length of alkyl. The efficiency is almost unaffected by pH
(Figure 10.2). The solubilities of methyl paraben, ethyl paraben, and propyl paraben in
water at 25°C are 2.5, 1.7, and 0.5 g/L, respectively (Davidson, 1993).
Sulfur dioxide and sulfites have been used for many centuries as fumigants,
especially as wine preservatives. The antioxidative effect of SO 2 and sulfites was
previously discussed. SO 2 and its various sulfites dissolve in water, and at low pH
levels yield sulfurous acid, bisulfite, and sulfite ions. At pH values less than 4.0 the
antimicrobial activity reaches its maximum. The antimicrobial action of SO 2 against
yeasts, molds, and bacteria is selective, and some species are more resistant than
others. SO 2 and sulfites are used in the preservation of a variety of food products.
Because of their flavor and negative health effects they are used for preservation as
an intermediate process in which subsequent processing such as boiling or acidifi-
cation removes the additive.
Organic acids are naturally present in plant material or formed during fermen-
tation processes. Some of these, such as citric, malic, tartaric, acetic, lactic, and
propionic acid, are very often used as chemical preservatives in the treatment and
processing of fresh fruits and vegetables. Usually, solutions containing combinations
of organic acids or an acid and its salt are applied to reduce the undesirable flavor

FIGURE 10.2Effect of pH on minimal inhibition concentration of selected preservatives.
(Adapted from Belitz, H.D. and Grosch, W., Food Chemistry, Springer, Berlin, 1999,^ Chap. 2.)

0

0.05

0.1

0.15

0.2

0.25

0246810

pH

Minimal inhibition concentration (%)

benzoic acid

sorbic acid

propyl paraben