at pH less than 4, chlorine gas increases. Fur-
thermore, the formation of Cl 2 is a safety
issue. Because there are substantial amounts
of hydrochlorous acid present when the pH
exceeds 6.5, sanitizing operations are nor-
mally executed in the pH range of 6.5 to 7.0.
The reaction time of chlorine-based sanitiz-
ers is temperature-dependent. Up to 52°C, the
reaction rate doubles for each 10°C increase in
temperature. Although hypochlorites are rela-
tively stable, Cl 2 solubility decreases rapidly
above 50°C.
The efficacy of a buffered sodium
hypochlorite solution to control bacterial
contamination was determined by Park et al.
(1991). They found this sanitizing solution to
be effective in reducing Salmonella enteri-
tidis. Their research reflected no adverse
effects on protein functionality, lipid oxida-
tion, and starch degradation after exposure
of food products to the sanitizing solution.
Furthermore, this sanitizer is non-film form-
ing without residual activity.
Active chlorine solutions are very effec-
tive sanitizers, especially as free chlorine and
in slightly acid solutions. These compounds
appear to act through protein denaturation
and enzyme inactivation. Chlorine sanitizers
are effective against gram-positive and
gram-negative bacteria, and conditionally
against certain viruses and spores. They are
low temperature tolerant, however, the avail-
able chlorine from hypochlorite and other
chlorine-releasing chemicals reacts with and
is inactivated by residual organic matter. If
the recommended volume and sufficient
concentration is applied, a sanitizing effect
can still be achieved. Only freshly prepared
solutions should be used. Storage of used
solutions may result in a decline in strength
and activity. Concentration of active chlo-
rine can be easily measured by use of test
kits to ensure application of the desired
concentration. Liquid chlorine, which is a
solution of sodium hypochlorite in water,
can be applied to processing and cooling
waters to prevent bacterial growth and slime
formation.
Inorganic chloramines are compounds
formed from the reaction of chlorine with
ammonia nitrogen;organic chloraminesare
formed through the reaction of hypochlor-
ous acid with amines, imines, and imides.
Bacterial spores and vegetative cells are more
resistant to chloramine than to the hypochlo-
rites. Chloramine T apparently releases
chlorine slowly. As a result, its lethal effects
are slow when compared with the hypochlo-
rites.
Other chloramine compounds are as
effective as, or more effective than, the
hypochlorites in deactivating microorgan-
isms. However, these compounds release
chlorine slowly and produce a slower kill
rate. The reduced activity of chlorine per-
mits the penetratation of organic matter,
which may be advantageous when they are
used against biofilms (Eifert and Sanglay,
2002). Sodium dichloroisocyanurate is more
active than sodium hypochlorite against
E. coli,S. aureus, and other bacteria.
Less is known about the antimicrobial
effects of chlorine dioxidethan about the
other chlorine compounds; however, interest
in this compound has increased. New chem-
ical formulations of this compound allow it
to be shipped to areas of use (rather than
being generated on site); consequently, it is
being used more in the food industry.Chlo-
rine dioxide (ClO 2 ) is known to have 2.5
times the oxidizing power of chlorine. This
compound is not as effective as chlorine at
pH 6.5, but at pH 8.5, ClO 2 is the most effec-
tive. Thus, ClO 2 appears to be less affected
by alkaline conditions and organic matter
than hypochlorites, making it a viable agent
for sewage treatment.
Examples of how chlorine dioxide sanitiz-
ers are produced are indicated by the reac-
tions that follow.