all in one assays.The exactchemical formulationsusedin the assays varywith
suppliers,but all containluciferin/luciferase,magnesiumions, buffering,sub-
strates, stabilisersand extractants (to removethe ATPfromlivingcells). They
varyin shelf-life, depending on precisecomposition and the temperatureand
manner of theirstorage. Typicalrefrigerated storagetimes wouldbe 6 months.A
number of manufacturers claim to have developed a test stable at room
temperature,althoughthis may varyconsiderablyamong countriesand climates.
ATPis a universal biochemical found in many, but not necessarily all,
foodstuffs.Highcounts can be foundin some freshfoods, e.g. tomatoes, while
other foods, especiallyhighlyprocessed foodssuchas fats, oils or sugar, contain
verylow amounts. Detergents/sanitisersusedin cleaning can havea similar
effect to the extractants usedin the testsand differentstudieshavedemonstrated
that commonly used cleaning chemicals can cause either quenching or
enhancementof the ATPsignal.It is thereforedesirable, for consistencyof
results, to ensurethat cleaningagents are removedby rinsingbeforetestingis
performed.The repeatability and reliabilityof the instrumentsand theirtestscan
varyconsiderably amongmanufacturersbut is generally superior to micro-
biologicalswabbing (Griffithet al., 1997).In the author's experience,problems
are more likely to be a reflectionof howthe cleaningand testinghavebeen
performed,ratherthanthe ATPtest system.The sensitivityof the instruments
and theirtestsis variable and therehas been discussion overexactly how
sensitive ATPtestsneedto be. The key requirementis that theyshould be able
to discriminate wellcleaned'frominadequatelycleaned', surfacesimportant
or relevant to a business.There is thereforea demandfor a certainminimum
sensitivity. Whether a test can be too sensitive is more debatable. Highly
sensitive tests,if available,could be adapted to make themmorespecific,e.g.
for microorganismsonlyor evenspecificpathogens.Highly sensitive testscould
also allowmore refined discriminationbetween cleanand marginallyunclean.
While test manufacturerswill provideguidanceon cleanbenchmark levels,
theyare usually best determined on site by the foodbusinessand thenusedas
the basis for continuousimprovement(see also Section36.4.3). ATPhas also
beenadaptedby one test manufacturer for the detection of allergen residues and
it is claimedthe test detects downto 0.1±5 ppmof allergen foodresidues.
36.3.2 Proteinand otherassays
Followingthe development and application of ATP bioluminescence as a
measure of cleanliness, otherchemicalassays/testsfor foodresiduecomponents
havebeeninvestigated.The stimulus is to developa non-instrument dependent
test, that is cheapand functional.A rangeof other chemicalresidues including
protein, reducingsugars,NADand phosphate, eitherindividually or in com-
bination,are now usedas the basisfor rapidcleaning tests. Usuallythe tests lead
to the productionof a single, or sequence of, colouredend-productswithina
specified time(1±10minutes). The colourchanges can be qualitatively assessed
visually.Thiscan be subjective and the optionto use a cheapsample instrument
606 Handbookof hygiene controlin the foodindustry