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Worksheet.pdf - Practical l WORKSI{EET Pa-ara* Nome: S9s...

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PracticallWORKSI{EETNome:Pa-ara*LATABLLS9sLzL€lPARTl:TESTINGFORQUALITYIHYGIENE INDICATORSANDFORLEVELSOFS.AUREUSquestion1.Explainthe difference between'validation'and'verification' inrelationtonon-Australian Standard(non-AS)methodsused infood testing.ooo,Jaft101ol$,ttA-L+oO{a)i-bcl,oro-rto-P^olr-r,nrnlt/qALpo0+"frttooLA{e./yt-aapLat-sa-ppLLoao^tr.<r{-ouu-'11Cl^D.VpILPohc*a'v'*Grat:h'ta'-14d\-..rrrir.r.t,{.1Studentnumber:Questions1to20[90MARKS]?vaz,Liea-Lfvc!f"iA6marxslI
QUESTIONS2AND 3:Resultsfor TotalCountsDay2: PetrifilmrMAPCquestion2. Enteryourcountsfor the PetrifilmAPCplatesforeachdilutioninthe tableshown below. Thenusingthese data, calculate theAPC/gramofsaladshowingyourcalculationsaccordingtotheformulaintheASmethod.Recordcolony countsforeachdilution:Dilution10-110-210410-sColonyCountzoe"tgt{ICirclethedilution/syouwilluseforyourcalculationsbasedon theformulaasdescrlbedinAS5013.142Sedion \0.3.2.2.2andinothersubsectionsof10.3.2.Thisformulaisshownbelow.Part A assumesyouhaveadequate counts(colonynumbers)tobe abletouseTWOadjacentdilutions(i.e.countsarewithinthe minimumand maximum numberthresholds).PartBisusedifonlyone plateisabletobecounted.PARTAFormulaforcalculatingCFU/gramforAPGcoliforms,E.coliandS.oureus observed infoodsampleNTCv(n1+0.1nr) dIN=Number of colonies per mlorgofproduct!IC=Sumofallcoloniesontheplates counted.Chooseyourfirstplateto countbychoosingthe dilutionthathasanappropriate growncolonies. Countthenumberofcolonies. Notethe dilutionofthisplate.Chooseyoursecondcountasthenumberofcoloniesgrownonthenextdilutionafter this.Iv=volumeinoculatedontoeach plate(egforpourplatesitisusually1mL andforspreadplateslsusually 0.1mL)Inr=Numberofplatesusedfor the first dilution counted(ietheplatethatshowsshowing15-300colonies)*(thisis1ifyouuseforsingle platesforeachdilutionand2if.youusedupli6ateplates)In2=t{urn!s1qfplatesusedfor theseconddilution counted10-3)3o6
PART B.lf thereisonly oneplatewithcoloniestocount(noneonthenextdilution)thenusethe formulaandmultiply thevalue(v)by1(n1)tocalculatethetotalplatecountin onegram(orml) of sampleShowyourcalculationstoarriveatyouranswerusingtheformulav(qttotq)ALc--+oLtl$--9o1VoIan-!nl,(qt.-ldz-tg'4./roo"o'o1APC/gramofsalad=?eilaA(5marks)Answer:Tt"ltt4-r..t=3eltIr1o'txl)o'ot=3eYr'lxo.ol--:*.L*,LLLlL6.otlt24too'oocu-Lobd)^'''/'t-t1"-2.pooOotvL)u-?td-tb?taLL4aLarlla*.cgto-?,dr4uil)-t,?S*n2-Eto'3lo-'(rL.!no"-zO^-L/-<oLcLtt<eylo-3ooE?cpl-p,it*1{.p,rt&^.oLA&ur"i4qL9t1^-2-rd=Dilutionfromwhich thefirstcountswere obtained(lethe dilutlonofthecountfornr1ORN=-5.

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