3M Petrifilm 6475 - Interpretation; Specific Instructions for Validated Methods; NF Validation by AFNOR Certification

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(English)
EN
Interpretation
1. 3MPetrilmRYMPlatescanbecountedusingastandardcolonycounterorotherilluminatedmagnier.Gridlinesarevisiblewiththeuseofa
backlighttoassistwithestimatedenumeration.
2. Do not count colonies on the foam dam since they are removed from the nutrient medium.
3. Todifferentiateyeastandmoldcoloniesonthe3MPetrilmRYMPlate,lookforoneormoreofthefollowingcharacteristics:
YEAST MOLD
Small colonies Largecolonies
Colonies have dened edges Colonies have diffuse edges
Pink/tantoblue/greenincolor Blue/greentovariableuponprolongedincubation
Colonies appear raised (3 dimensional) Coloniesappearat
Colonies have a uniform color Colonieshaveadarkcenterwithdiffusededge
4. Read yeast and mold results at 48 hours. Certain slower growing yeasts and molds may appear faint at 48 hours. To enhance interpretation
ofthesemoldsallowforanadditional12hoursofincubationtime.Ifa60hourtime-pointforinterpretationisnotconvenient,extendingthe
incubation time to 72 hours is an acceptable alternative.
5. Thecirculargrowthareaisapproximately30cm
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. 3MPetrilm RYM Plates containing greater than 150 colonies can either be estimated or
recordedasTooNumerousToCount(TNTC).Estimationcanbedonebycountingthenumberofcoloniesinoneormorerepresentativesquares
anddeterminingtheaveragenumberpersquare.Theaveragenumbercanbemultipliedby30todeterminetheestimatedcountperplate.Ifa
moreaccuratecountisrequired,thesamplewillneedtoberetestedathigherdilutions.Whenthesamplecontainssubstantialamountsofmold,
depending on the type of mold, the upper countable limit may be lowered at user discretion.
6. Foodsamplesmayoccasionallyshowinterferenceonthe3MPetrilmRYMPlates,forexample:
a) auniformbluebackgroundcolor(oftenseenfromtheorganismsusedinculturedproducts)theseshouldnotbecountedasTNTC.
b) intense, pinpoint blue specs (often seen with spices or granulated products).
7. Whennecessary,coloniesmaybeisolatedforfurtheridentication.Liftthetoplmandpickthecolonyfromthegel.
Specic Instructions for Validated Methods
AOAC® Ofcial Methods (OMA)
SM
#2014.05
AOAC® Research Institute (RI) Performance Tested Method (PTM)
SM
#121301
InAOACOMAandPTMstudies,the3MPetrilmRYMPlatemethodwasfoundtobeequivalenttoorbetterthantheaveragelogcountsofthe
ISO21527:2008parts1and2andtotheFDABAMChapter18referencemethodsat48and60hours.
Scope of Validation:
Yogurt, frozen bread dough, fermented salami, sour cream, ready-made pie, frozen ground beef patties, almonds, sandwiches, sliced apples, and
dehydrated soup.
Incubation:
Incubate 3MPetrilm RYM Plates between 48 and 60 hours at 25°C +/-1 °C or 28°C +/-1°C.
Interpretation:
Platescontaininggreaterthan150coloniescaneitherbeestimatedorrecordedattoonumeroustocount(TNTC).Estimationcanbedoneby
countingthenumberofcoloniesinoneormorerepresentativesquaresanddeterminingtheaveragenumberpersquare.Theaveragenumbercanbe
multipliedby30todeterminetheestimatedcountperplate.Ifamoreaccuratecountisrequired,thesamplecanberetestedathigherdilutions.
NF Validation by AFNOR Certication:
NFValidationcertiedmethodincompliancewithISO16140
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in comparison to 21527 part 1 and part 2
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UsethefollowingdetailswhenimplementingtheaboveinstructionsforUse:
Scope of the validation:
Allhumanfoodproducts,animalfeedandenvironmentalproducts(primaryproductionsamplesexcepted)
Sample preparation:
UseonlyISOlisteddiluents
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Incubation:
Incubate 3MPetrilm RYM Plates between 60 and 72 hours at 25°C +/-1 °C or 28°C +/-1°C.
The plates can be stored in the incubator up to 5 days.