2009_Book_FoodChemistry

8.12 Antimicrobial Agents 453
centrates or purée. The form of application is
SO 2 , Na 2 SO 3 , K 2 SO 3 ,NaHSO 3 ,Na 2 S 2 O 5 and
K 2 S 2 O 5 at levels of 200 ppm or less.
SO 2 is added in the course of wine making prior
to must fermentation to eliminate interfering microorganisms.
During wine fermentation with selected
pure yeast cultures, SO 2 is used at a level of
50–100 ppm, while 50–75 ppm are used for wine
storage.
SO 2 is not only antimicrobially active, but
inhibits discoloration by blocking compounds
with a reactive carbonyl group (Maillard reaction;
nonenzymatic browning) or by inhibiting
oxidation of phenols by phenol oxidase enzymes
(enzymatic browning).
8.12.7 Diethyl (Dimethyl) Pyrocarbonate
Diethyl pyrocarbonate (DEPC or diethyl dicarbonate)
is a colorless liquid of fruit-like or ester
odor. Its antimicrobial activity covers yeasts (10–
100 ppm), bacteria (Lactobacilli: 100–170 ppm)
and molds (300–800 ppm). The levels of the compound
required for a clear inhibition are given
in brackets. Diethyl pyrocarbonate readily hydrolyzes
to yield carbon dioxide and ethanol:
Since diethyl carbonate may be a teratogenic
agent and ethyl urethane is a carcinogen, the
use of diethyl pyrocarbonate is discussed under
toxicological aspects. The compound should
be replaced by dimethyl pyrocarbonate, since
methyl urethane, unlike ethyl urethane, is not
carcinogenic.
Both compounds are used in cold pasteurization
of fruit juices, wine and beer at a concentration of
120–300 ppm.
8.12.8 Ethylene Oxide, Propylene Oxide
These compounds are active against all microorganisms,
particularly vegetative cells and spores,
and also against viruses. Propylene oxide is somewhat
less reactive than ethylene oxide.
Since they are efficient alkylating agents, the pure
compounds are very toxic. After application,
all the residual amounts must be completely
removed. The glycols resulting from their hydrolysis
are not as toxic (ethylene glycol: LD 50
forratsis8.3g/kg body weight). Toxic reaction
products can be formed, as exemplified by
chlorohydrin obtained in the presence of chloride:
(8.34)
or it reacts with food ingredients. In alcoholic
beverages it yields a small amount of diethyl carbonate:
(8.35)
In the presence of ammonium salts, DEPC can
form ethyl urethane in a pH-dependent reaction:
(8.36)
(8.37)
In addition, some essential food constituents
react with formation of biologically inactive
derivatives. Examples are riboflavin, pyridoxine,
niacin, folic acid, histidine or methionine.
However, these reactions are not of importance
under the conditions of the normal application of
ethylene oxide or propylene oxide.
Both compounds are used as gaseous sterilants
(ethylene oxide, boiling point 10.7 ◦ C; propylene
oxide, 35 ◦ C) against insects and for gaseous
sterilization of some dehydrated foods for which
other methods, e. g. heat sterilization, are not
suitable. Examples are the gaseous sterilization
of walnuts, starches, dehydrated foods (fruits
and vegetables) and, above all, spices, in which
a high spore count (and plate count in general)
is often a sanitary problem. The sterilization is
carried out in pressure chambers in a mixture
with an inert gas (e. g. 80–90% CO 2 ). The need
to remove the residual unreacted gas (vacuum,