The main considerations in choosing a chemical disinfectant for use in
the food industry are:
(1) Its microbiological performance – the numbers and types of
organisms to be killed.
(2) How toxic is it and what is its effect on the food?
(3) What is its effect on plant – does it stain or corrode equipment?
(4) Does it pose any hazard to staff using it?
(5) Is it adversely affected by residual soil?
(6) What are the optimal conditions for its use,i.e.temperature,
contact time, pH, water hardness?
(7) How expensive is it?Some of these characteristics are summarized in Table 11.7.
All disinfectants are deactivated to some extent by organic matter.
This is why they are best used after thorough cleaning has removed most
of the soil.
Chlorine in the form of hypochlorite solution is the cheapest effective
disinfectant with a broad range of antimicrobial activity which includes
spores. The active species is hypochlorous acid (HOCl) which is present
in aqueous solutions at pH 5–8. It is corrosive to many metals including
stainless steel although this can be minimized by using it at low concen-
trations, at alkaline pH, at low temperature and with short contact times.
For most purposes an exposure of 15 minutes to a solution containing
100 mg l^1 available chlorine at room temperature is sufficient.
Organochlorine disinfectants such as the chloramines are generally
weaker antimicrobials but are more stable and less corrosive than
hypochlorite allowing longer contact times to be used.
In iodophors, iodine is dissolved in water by complexing it with a non-
ionic surfactant. Phosphoric acid is often included since the best bacte-
ricidal activity is observed under acidic conditions. To disinfect clean
surfaces a solution containing 50 mg l^1 available iodine at a pHo4is
usually required. The amber colour of iodophors in solution has two
useful functions: it provides a crude visual indication of the strength of
the solution and it will stain organic and mineral soils yellow indicating
where equipment has been inadequately cleaned. However, they can also
stain plastics and can taint some foods.
QUATs are highly stable with a long shelf-life in concentrated form.
They are non-corrosive and can therefore be used at higher temperatures
and with longer contact times than other disinfectants. However, at low
concentrations (o50mg l^1 ) and low temperatures they are less effective
against Gram-negative bacteria. This is not usually a problem under
normal conditions of use (150–250mg l^1 ; 4401 C; contact time 4 2 min),
422 Controlling the Microbiological Quality of Foods