although incorrect usage could result in a build up of QUAT-resistant
bacteria on equipment. Because of their surfactant properties, QUATs
(and amphoterics) adhere to food-processing surfaces even after rinsing.
This can be an advantage; in one study in a poultry plant, levels of
bacteria on plant were shown to continue decreasing for nine hours after
disinfection as a result of the effect of residual QUAT. In some areas
though, it can be a problem; residual QUAT or amphoteric may inhibit
starter culture activity in cheese and yoghurt production and can also
affect head retention on beer.
Biguanides are similar to QUATs but have greater activity against
Gram-negatives, although development of resistance has been noted
here too.
Amphoterics are surfactants with a mixed anionic and cationic char-
acter which are far less affected by changes in pH than other disinfectants.
Their high foaming characteristics make them unsuitable for some uses.
In modern food processing much equipment cleaning is automated in
the form of cleaning-in-place (CIP) systems. These are most readily
applied to cleaning and disinfecting plant which handles liquid foods and
have therefore found widest application in the brewing and dairy indus-
tries, although they are now appearing in meat processing plants. A CIP
system is a closed section of plant which can be cleaned by draining the
product followed by circulation of a sequence of solutions and water
rinses that clean and then disinfect the plant leaving it ready for resumed
production. Though the initial capital investment is high, CIP offers a
number of advantages. Its running costs are lower than traditional
cleaning procedures since labour costs are low and it gives optimal use
of detergents, disinfectants, water and steam. As it does not involve the
dismantling of plant prior to cleaning, CIP minimizes unproductive
‘down time’ and the risk of equipment damage during disassembly. It
is also safer since personnel are no longer required to perform the
sometimes hazardous operations of climbing up on to, or into, equip-
ment and, provided the system is correctly formulated, it gives a con-
sistent result with little chance of human error.
To ensure cleaning and disinfecting procedures are achieving the
desired result some form of assessment is necessary. The inadequacy of
visual inspection of equipment to determine its microbiological status
has already been alluded to. It is however worth noting that, with few
exceptions, if a surface is visually dirty it is also likely to be microbio-
logically dirty. Culturing micro-organisms removed from a cleaned
surface by swabbing, rinsing or a contact-transfer technique will give
an indication of the level of contamination, but only after sufficient time
has elapsed for the organisms to produce visible growth. Recently the use
of ATP bioluminescence has found increasing use in this area. It provides
a rapid measure of the hygienic status of a surface without having to
424 Controlling the Microbiological Quality of Foods