to measure, and/orrecord the results is availablefor some tests,if needed. The
subjectivityis mostvariablefor marginally uncleansurfaces,the clean or very
dirtybeingless subjective. Sometestsretain a swab-based format,whileothers
use test stripsof plasticor padsof absorbentmaterial impregnatedwithrelevant
reagents. Which,if any,of thesetestswill be of benefitto a foodbusinesswill
dependon a number of factors (seeTable 36.6),not leastof whichis the
sensitivityof the assay.Suchtests,if cheaperand instrument independent, may
findpotential use in foodserviceestablishments. Often criticisedfor poor
cleanliness,theyare the reported locationfor mostoutbreaksof foodpoisoning
(Griffith, 2000).
Of the non-ATPassays,proteindetectionmethods offerpotentialwherethe
foodresidues, e.g. poultry/meat/dairyproducts, are highin protein. In someof
the assays, otherfoodnon-protein,reducingcomponents mayalso bringabouta
colourchange. Some methodsmake use of an enhanced Buiretreaction.Under
alkalineconditionsthe peptidebondsof proteins form a complexwiththe
copperII (Cu2+) of the Buiretreagent, reducingit to CopperI (Cu+) ions. These
reactwithbicinchoninicacid,producing an intensepurplecolour.For this test,
the sloganif it's greenit's clean' is used.Otherproteintestsmake use of differentso calledproteinerrorindicator', dyes(e.g.tetrabromophenolblue),
whichchangecolour in the presenceof proteinat a particular pH. Thesetests
maybe swab-based, althoughsome versionsuse test stripsor pads.Depending
uponthe foodexamined, proteintestsmaybe more or less sensitivethanATP
bioluminescence (Mooreand Griffith,2002c). The intensity of the colour and its
speedof production provide an indicationof the levelof soilingalthoughresults
are usuallyjust pass/fail.
NAD(nicotinamide adenine dinucleotide)and relatedformsare chemical
residues, also widely distributedin biological materials, including foodsand
microorganisms.Hence,the levelof NADon a surface provides a measure of
organic soiling. NAD is detectedin a chemicalreaction leadingto the produc-
tion of a pink/purplecolouron a test strip,within5 minutes. As withthe other
chemical residuedetection kits, lack of a positivereactiondoesnot represent
lack of microorganisms.This test maybe moreor less sensitive thanotherrapid
chemical testsand its usefulnessneedsto be trialled and will dependuponthe
typeof foodsproduced.
Otherswab-basedtestscan be usedto detect eitherglucose or glucoseand
lactose, the latter being of practicalbenefit to the dairyindustry. Resultsare
obtained within60 seconds. Unfortunately, because of the natureof the colour
reaction,the results are readif it turnsgreen it isn'tclean',whichcan leadto confusion withprotein test results!In mostcases, the test is less likelyto be as sensitive as the equivalentATPassaybut it is claimedthat for manyfood residues, it is nearlyas goodand is rapidand non-instrumentbased. Anotheroptionis a test stripcontaining enzymes that can detectphosphate and carbohydrates.This makes use of capillary actiontosuck'foodresidues
froma wetted surfaceontotest reagents.A wettingindicator is also incorporated
into the test strip, goingdarkgreywhensufficiently wet, the mainfoodresidue
Improvingsurfacesamplingand detection of contamination 607