are likely to be required to demonstrate directlythe presenceof the offending
allergen,ratherthana markermaterial.
Thereversetranscriptasepolymerase chainreaction(RT-PCR) assay has
recentlybecomethe subjectof considerableinterest, and is described elsewhere
in this book.It takes advantage of amplificationof any relevant(species) DNA
presentin the foodof interestto the pointwhereit can be detected.It can also be
usedin a modewhichcan be consideredsemi-quantitative. However, in relation
to allergens,it relieson an implicit assumption that the presenceof DNAin a
processed fooddenotesthe presenceof (allergenic)protein,a contention that
needsexperimentaljustification.
23.4.3 Limitof detection
The limitof detectionof any assayis an importantparameter,but it needsto be
considered together withthe other parameters that makeup the assay.Again,the
purpose of the assay should dictatethis factor, as it doesthe others. For most
purposes, suchas monitoring the effectivenessof allergen control measures, or
verifyingcompliance withset limits, it would be reasonable for the detection
limitto be suchthat the assay coulddetectallergenic material in an amount in a
portionof foodthat was closeto the lowestamountshownto provokesome
reactionundercontrolledclinicalconditions.This,of course, begsthe question as
to what thoselevelsare, and to what extentany uncertaintyin determining
minimumprovoking dosesshould alsobe allowedfor. Minimumprovoking
dosesvaryconsiderably among individuals15,16and Bindslev-Jensenet al.^8 have
recentlydescribed theircumulative frequency versus log-normaldosein the
populationof allergicpatientsas a sigmoidal log-normalplot.The implication of
this distribution is that thereis a smallproportion of individualswho will respond
to verysmallamountsof allergen.Assayscouldbe developedto detectsuch
smallamounts, but, evenleavingasidepossible technicalissues of signal to noise
ratio,it is questionablewhether suchsensitivityis actually required,exceptfor
forensic purposes. A recentsuggestion,basedon clinicalfindings,^17 proposed
that measuresto minimise the inadvertent presenceof allergen in industrial food
manufacture shouldaim to protect95%of the allergicpopulation.On that basis,
the lowestlevelsthat residual allergenshouldnot exceed wereof the orderof 5
ppmprotein,a requirementthat mostcurrentcommercially available assays
meet,assuming minimal losses duringextraction.It shouldalso be borne in mind
that the conceptof a validlowerdetectionlimitis onlymeaningfulin the context
of an assay developedto detecta representativerangeof proteinsin a food
product. Assaysdeveloped to detecta single protein couldbe verydifficult to
interpret in thesecircumstances, for reasonsalreadydiscussed.
23.4.4 Characteristics of the idealallergen detection assay
Havingconsideredvariousparametersof assays for the detectionof allergenic
residues, it is appropriateto examine whatan idealassaymightlooklike.
However, simplyin formulatingsucha question, one is inevitablydrawnto
Managingrisksfromallergenicresidues 371