(iii)cationic– quaternary ammonium compounds (QUATs) which
have a positive charge in solution and are used mainly for their
bacteriostatic and bacteriocidal activity rather than their clean-
ing properties.Detergent preparations also often include alkalis such as sodium
hydroxide, sodium silicates, or sodium carbonate which assist in sol-
ubilizing organic material such as fats and proteins. Acids are used in
other formulations designed to remove the tenacious mineral scales such
as milkstone which build up on surfaces, particularly heated ones, after
repeated use.
Phosphates have a number of useful functions in detergents though
their subsequent environmental impact can pose problems. Detergent
performance is improved by sequestering agents which chelate calcium
and magnesium ions and prevent the formation of precipitates. Poly-
phosphates are often used for this purpose, although ethylenediamine
tetraacetic acid (EDTA) and gluconic acid are alternatives which have
the advantages of heat stability and compatibility with QUATs. Poly-
phosphates also inhibit the redeposition of soil; a role for which sodium
carboxymethyl cellulose is sometimes included.
Several other factors contribute to an effective cleaning procedure in
addition to the physico-chemical activity of the detergent solution. Heat
generally improves the efficiency of cleaning, particularly with fat-
containing soils, although the temperature used must be compatible
with the detergent, the soil type, and the processing surface being
cleaned. Mechanical energy in the form of shear forces created by
turbulence, scrubbing or some other form of agitation considerably
assists in the cleaning process. For smaller items of equipment this can
be done manually but for larger areas and pieces of equipment some
form of power cleaning is necessary. This may involve the use of a high
pressure low volume (HPLV) jet of water or detergent solution. HPLV
systems operate at pressures in the range 40–100 bar (kg cm^2 ) with flow
rates between 5 and 90 1 min^1 and are best suited for cleaning equip-
ment where it is necessary to direct a powerful jet into relatively inac-
cessible areas (though hygienic design should minimize these). They are
also used to rinse off detergents applied to equipment in the form of gels
or foams; systems which give longer contact times between detergent and
soil than would be obtained simply by spraying with an aqueous deter-
gent solution. Gel or foam cleaning is particularly suited to use with
more recalcitrant soils and on non-horizontal equipment surfaces where
conventional detergent solutions would quickly run off.
Low pressure/high volume (LPHV) cleaning (E5 bar;E500 l min^1 )
is suitable for areas with a low level of soiling with water soluble residues
or washing light debris to a floor drain.
420 Controlling the Microbiological Quality of Foods