Lecture : 3 Food Microbiology

Lecture : 3 Food Microbiology

I.PREDOMINANTMICROORGANISMSINDIFFERENTSOURCES

A.Plants(FruitsandVegetables)

Theinsidetissueoffoodsfromplantsourcesareessentiallysterile,exceptforafew porousvegetables(e.g.,radishesandonions)andleafyvegetables(e.g.,cabbageand Brusselssprouts).1–5Someplantsproducenaturalantimicrobialmetabolitesthatcan limitthepresenceofmicroorganisms.Fruitsandvegetablesharbormicroorganisms onthesurface;theirtypeandlevelvarywithsoilcondition,typeoffertilizersand waterused,andairquality.Molds,yeasts,lacticacidbacteria,andbacteriafrom generaPseudomonas,Alcaligenes,Micrococcus,Erwinia,Bacillus,Clostridium,and Enterobactercanbeexpectedfromthissource.Pathogens,especiallyofenteric types,canbepresentifthesoiliscontaminatedwithuntreatedsewage.Diseasesof theplants,damageofthesurface(before,during,andafterharvest),longdelay betweenharvestingandwashing,andunfavorablestorageandtransportconditions afterharvestingandbeforeprocessingcangreatlyincreasemicrobialnumbersas wellaspredominanttypes.Improperstorageconditionsfollowingprocessingcan alsoincreasetheirnumbers.

Propermethodsusedduringgrowing(suchasuseoftreatedsewageorother typesoffertilizers),damagereductionduringharvesting,quickwashingwithgood- qualitywatertoremovesoilanddirt,andstorageatlowtemperaturebeforeand afterprocessingcanbeusedtoreducemicrobialloadinfoodsofplantorigin.

B.Animals,Birds,Fish,andShellﬁsh

Foodanimalsandbirdsnormallycarrymanytypesofindigenousmicroorganisms inthedigestive,respiratory,andurinogenitaltracts,theteatcanalintheudder,as wellasintheskin,hooves,hair,andfeathers.Theirnumbers,dependingonthe speciﬁcorgan,canbeveryhigh(largeintestinalcontentscanhaveashighas1010bacteria/g).Many,ascarriers,canharborpathogenssuchasSalmonellaserovars,

pathogenicEscherichiacoli,Campylobacterjejuni,Yersiniaenterocolitica,andList- eriamonocytogeneswithoutshowingsymptoms.Layingbirdshavebeensuspected ofasymptomaticallycarryingSalmonellaEnteritidisintheovariesandcontaminat- ingtheyolkduringovulation.Diseasesituations,suchasmastitisincowsand intestinal,respiratory,anduterineinfections,aswellasinjurycanchangetheecology ofnormalmicroﬂora.Similarly,poorhusbandryresultinginfecalcontaminationon thebodysurface(skin,hair,feathers,andudder)andsupplyingcontaminatedwater andfeed(e.g.,contaminatedwithsalmonellae)canalsochangetheirnormalmicro- bialﬂora.

Fishandshellﬁshalsocarrynormalmicroﬂorainthescales,skin,anddigestive tracts.Waterquality,feedinghabits,anddiseasescanchangethenormalmicrobial types and level. Pathogens such asVibrio parahaemolyticus,Vib. vulniﬁcus,andVib. choleraeareofmajorconcernfromthesesources.Manyspoilageandpathogenic microorganismscangetintofoodsofanimalorigin(milk,egg,meat,andﬁshery products)duringproductionandprocessing.Milkcanbecontaminatedwithfecal materialsontheuddersurface,eggshellswithfecalmaterialduringlaying,meat withtheintestinalcontentsduringslaughtering,andﬁshwithintestinalcontents duringprocessing.Becauseofitsspeciﬁcnature,contaminationoffoodsofanimal sourceswithfecalmaterialsisviewedwithconcern(possiblepresenceofenteric pathogens).

Inadditiontoentericpathogensfromfecalmaterials,meatfromfoodanimals andbirdscanbecontaminatedwithseveralspoilageandpathogenicmicroorganisms fromskin,hair,andfeathers,namelyStaphylococcusaureus,Micrococcusspp., Propionibacteriumspp.,Corynebacteriumspp.,andmoldsandyeasts.

Preventionoffoodcontaminationfromthesesourcesneedstheuseofeffective husbandryofliveanimalsandbirds,whichincludesgoodhousingandsupplyof uncontaminatedfeedandwater.Also,testinganimalsandbirdsforpathogensand cullingthecarriersareimportantinreducingtheincidenceofpathogenicmicroor- ganismsinfoods.Thoroughcleansingusinggood-qualitywaterforwashingcar- casses(preferablywithacceptableantimicrobialagents);hairremoval;feather removal;carefulremovalofdigestive,urinogenital,andrespiratoryorganswithout contaminatingtissues;removalofcontaminatedparts;andpropersanitationduring theentireprocessingstagearenecessaryduringslaughterto keepmicrobialquantity andqualityatdesirablelevels.Propercleaningoftheudderbeforemilking,cooling milkimmediatelyaftermilking,processingassoonaspossible,andsanitizationat allstagesareimportanttokeepmicrobiallevelslowinmilk.Eggsshouldbecollected soonafterlayingandwashedandstoredasperrecommendedprocedures.

Fishandmarineproductsshouldbeharvestedfromunpollutedandrecommended water.Propersanitationshouldbeusedduringprocessing.Theyshouldbestored properlytopreventfurthercontaminationandmicrobialgrowth.Icetobeusedfor storageshouldbeproducedfrompotablewater.

C.Air

Microorganismsarepresentindustandmoisturedropletsintheair.Theydonot growindust,butaretransientandvariable,dependingontheenvironment.Theirlevel is controlled by the degree of humidity, size and level of dust particles, temperature and air velocity, and resistance of microorganisms to drying. Generally, dry air

with low dust content and higher temperature has a low microbial level. Spores of Bacillus spp., Clostridium spp., and molds, and cells of some Gram- positive bacteria(e.g., Micrococcus spp. and Sarcina spp.), as well as yeasts, can be predominantly present in air. If thesurroundings contain a source of pathogens (e.g., animal and poultry farms or a sewage-treatment plant), different types of bacteria, including pathogens and viruses (including bacteriophages), can be trans- mitted via the air. Microbial contamination of food from the air can bereducedbyremovingthe potentialsources,controllingdustparticlesintheair(usingﬁlteredair),using positiveairpressure,reducinghumiditylevel,andinstallingUVlight.

D.Soil

Soil, especially the type used to grow agricultural produce and raise animals and birds, contains several varieties of microorganisms. Because microorganisms can multiply in soil,theirnumberscanbeveryhigh(billions/g).Manytypesofmolds, yeasts,andbacterialgenera(e.g.,Enterobacter,Pseudomonas,Proteus,Micrococcus,Enterococcus,Bacillus,andClostridium)canenterfoodsfromthesoil.Soil contaminatedwithfecalmaterialscanbethesourceofentericpathogenicbacteria andvirusesinfood.Sedimentswhereﬁshandmarinefoodsareharvestedcanalso beasourceofmicroorganisms,includingpathogens,inthosefoods.Differenttypes ofparasitescanalsogetinfoodfromsoil.Removalofsoil(andsediments)by washingandavoidingsoilcontaminationcanreducemicroorganismsinfoodsfrom thissource.

Lecture : 3 Food Microbiology

E- Sewage

Sewage,especiallywhenusedasfertilizerincrops,cancontaminatefoodwith microorganisms,themostsigniﬁcantofwhicharedifferententeropathogenicbacteriaandviruses.Thiscanbeamajorconcernwithorganicallygrownfoodand manyimportedfruitsandvegetables,inwhichuntreatedsewageandmanuremight beusedasfertilizer.Pathogenicparasitescanalsogetinfoodfromsewage.

Toreduceincidenceofmicrobialcontaminationoffoodsfromsewage,itisbetter nottousesewageasfertilizer.Ifused,itshouldbeefﬁcientlytreatedtokillthe pathogens.Also,effectivewashingoffoodsfollowingharvestingisimportant.

Water

Waterisusedtoproduce,process,and,undercertainconditions,storefoods.Itis usedforirrigationofcrops,drinkingbyfoodanimalsandbirds,raisingﬁsheryand marineproducts,washingfoods,processing(pasteurization,canning,andcooling ofheatedfoods)andstorageoffoods(e.g.,ﬁshonice),washingandsanitationof equipment,andprocessingandtransportationfacilities.Waterisalsousedasan ingredientinmanyprocessedfoods.Thus,waterqualitycangreatlyinﬂuencemicrobial quality of foods. Contamination of foods with pathogenic bacteria, viruses, and parasites from water has been recordedWastewatercanberecycledforirrigation.However,chlorine-treatedpotable water(drinkingwater)shouldbeusedinprocessing,washing,sanitation,andasan ingredient.Althoughpotablewaterdoesnotcontaincoliforms and pathogens (mainly enteric types), it can contain other bacteria capable of causing food spoilage, such as Pseudomonas, Alcaligenes, and Flavobacterium.Improperly treated water can contain pathogenic and spoilage microorganisms.

Toovercometheproblems,many foodprocessorsusewater,especiallyasaningredient,thathasahighermicrobial qualitythanthatofpotablewater.

D.Humans

Betweenproductionandconsumption,foodscomeincontactwithdifferentpeople handlingthefoods.Theyincludenotonlypeopleworkinginfarmsandfood- processingplants,butalsothosehandlingfoodsatrestaurants,cateringservices, retailstores,andathome.Humancarriershavebeenthesourceofpathogenic microorganismsinfoodsthatlatercausedfoodbornediseases,especiallywithready- to-eatfoods.Improperlycleanedhands,lackofaestheticsenseandpersonalhygiene, anddirtyclothesandhaircanbemajorsourcesofmicrobialcontaminationinfoods. Thepresenceofminorcutsandinfectioninhandsandfaceandmildgeneralized diseases(e.g.,ﬂu,strepthroat,orhepatitisAinanearlystage)canamplifythe situation.Inadditiontospoilagebacteria,pathogenssuchasS.aureus,Salmonella serovars,Shigellaspp.,pathogenicEsc.coli,andhepatitisAcanbeintroducedinto foodsfromhumansources.

Propertrainingofpersonnelinpersonalhygiene,regularcheckingofhealth,and maintainingefﬁcientsanitaryandaestheticstandardsarenecessarytoreducecontaminationfromthissource.

E.FoodIngredients

Inpreparedorfabricatedfoods,manyingredientsoradditivesareincludedin differentquantities.Manyoftheseingredientscanbethesourceofbothspoilage andpathogenicmicroorganisms.Variousspicesgenerallyhaveveryhighpopulations ofmoldandbacterialspores.Starch,sugar,andﬂourmighthavesporesofthermophilicbacteria.Pathogenshavebeenisolatedfromdriedcoconut,egg,andchocolate.

Theingredientsshouldbeproducedundersanitaryconditionsandgivenantimicrobial treatments. In addition, setting up acceptable microbial speciﬁcations for the ingredientswillbeimportantinreducingmicroorganismsinfoodfromthissource.

F.Equipment

Awidevarietyofequipmentisusedinharvesting,slaughtering,transporting,processing,andstoringfoods. Manytypesofmicroorganismsfromair,rawfoods,water, andpersonnelcangetintotheequipmentandcontaminatefoods.Dependingonthe environment(moisture,nutrients,andtemperature)andtime,microorganismscan multiplyand,evenfromalowinitialpopulation,reacha highlevelandcontaminate largevolumesoffoods. Also,whenprocessingequipmentisusedcontinuouslyfor alongperiodoftime,microorganismsinitiallypresentcanmultiplyandactasa continuoussourceofcontaminationintheproductproducedsubsequently. Insome equipment,smallparts,inaccessiblesections,andcertainmaterialsmightnotbe efﬁcientlycleanedandsanitized.Thesedeadspotscanserveassourcesofboth pathogenicandspoilagemicroorganismsinfood. Smallequipment,suchascutting boards,knives,spoons,andsimilararticles,becauseofimpropercleaning,canbe sourcesofcrosscontamination.Salmonella,Listeria,Escherichia,Enterococcus, Micrococcus,Pseudomonas,Lactobacillus,Leuconostoc,Clostridium,Bacillusspp., andyeastsandmoldscangetinfoodfromequipment.

Propercleaningandsanitationofequipmentatprescribedintervalsareimportant toreducemicrobiallevelsinfood.Inaddition,developingmeanstopreventorreduce contaminationfromair,water,personnel,andinsectsisimportant.Finally,indesigningtheequipment,potentialmicrobiologicalproblemsneedtobeconsidered.

G.Miscellaneous

Foodsmightbecontaminatedwithmicroorganismsfromseveralothersources, namelypackagingandwrappingmaterials,containers,ﬂies,vermin,birds,house pets,androdents.Manytypesofpackagingmaterialsareusedinfood.Becausethey areusedinproductsreadyforconsumptionandinsomecaseswithoutfurther heating,propermicrobiologicalstandards(orspeciﬁcations)forpackagingmaterials arenecessary.Anyfailuretoproducemicrobiologicallyacceptableproductscan reducethequalityoffood.Flies,vermin,birds,androdentsinfoodprocessingand foodpreparationandstoragefacilitiesshouldbeviewedwithconcernastheycan carrypathogenicmicroorganisms.Housepetscanalsoharborpathogens;proper careshouldbetakennottocontaminatefoodfromthissource.