《Food Spoilage and Preservation Lecture》由会员分享，可在线阅读，更多相关《Food Spoilage and Preservation Lecture（52页珍藏版）》请在金锄头文库上搜索。
1、FoodSpoilageandPreservationDrJamesDooleySchoolofBiomedicalSciences,UniversityofUlster,ColeraineFoodSpoilageandPreservationAnessentialelementofmodernsocietyNotappreciatedbymostindividualsAchangingenvironmentrequiringconstantinnovationWillalwaysbeaproblemforhumansHunter-Gatherersocietynsupportedlownum
2、bers/self-sufficientnlimitedspecialisationnunreliableIndustrialandAgriculturalsocietynsupportshighnumbers/produceexcessnsupportsspecialisationngenerallypredictableFoodVitaminsProteinsCarbohydrateLipidsHumanGrowthEnergyBuildingmaterialsFoodVitaminsProteinsCarbohydrateLipidsEnergyBuildingmaterialsMicr
3、obialGrowthWhataremicrobes?“OrganismsthataretoosmalltobeseenwiththenakedeyeBacteriaVirusesFungiProtozoaWhatarebacteria?UnicellularorganismsVerysmall!n1-10micronsEnormousdiversitynShapenHabitatnNutritionManybacteriarequiresimilargrowthandnutritionconditionstohumans(verymanydonot!)Light Microscopex 1,
4、000Wheredowefindbacteria?Everywhere!nSoilnPlantrootsnWaternBodiesofanimals,fish,birdsetc,nHotspringsnDeadSeanHydrothermalventssporesEndosporeformationsome bacteria produce endosporesresponse to stressvery resistant to heat121oCvery resistant to harsh chemicals, drying, radiationcan remain dormant fo
5、r a long time (years)endospore - forming bacteria are common in soilWhataremicrobes?“OrganismsthataretoosmalltobeseenwiththenakedeyeBacteriaVirusesFungiProtozoaGeneralfeaturesofFungiunicellular(yeasts)andmulticellular(moulds)Non-photosynthetic,plant-likeorganismsMulticellular,filamentousorganismsNor
6、mallyinhabitantsofthesoil,rhizosphereandwaterCantolerateacidicanddryconditionsFungiinNatureMetabolicby-productsformtherawmaterialformanyindustries:nethanolnantibioticsnenzymes(washingpowdersetc.)nsolventsnfoodflavoursnCholesterol-loweringdrugsmevacorFungi are the main organisms involved in thedecay
7、of organic material and the recycling ofessentialelements(C,N,etc.)Yeast are good model organisms for geneticmanipulation.FungiinNatureMicro-organismsandfoodAgentsoffoodproductionMicro-organismsandfoodAgentsofdiseaseMicro-organismsandfoodAgentsoffoodspoilageFoodSpoilageandHowtoPreventitWeneedtoknowa
8、bouthowspoilageorganismsliveWeneedtounderstandtheirbiologyWeneedMicrobiologists!LaboratorystudyofbacteriaBacterialgrowthDoublingisaBigDealSomebacteriacandoubleevery30minBacterialgrowthBinaryfissionnDivideintwoGrowthratevariesnEscherichia colin20minutesnMycobacterium tuberculosisn15hoursWhatdobacteri
9、aneedtogrow?Sourceofnutrientsnaminoacids,sugars,lipids,vitaminsnreleasedbyactionofenzymesoperatingoutsidethecellCorrecttemperaturenBacteriagrowwithintemperaturerangesnmesophiles(10-45oC)npsycrophiles(0-20oC)Whatdobacterianeedtogrow?pHAbsenceoftoxicchemicalsCorrectatmosphere(O2)nAerobicnBacillusnAnae
10、robicnClostridiumnfacultativeanaerobesnSalmonellaConsequencesofbacterialgrowthMoreBacteria!NutrientsSuitableEnvironmentTimeConsequencesofbacterialgrowthinfoodNutrients:Starch,proteinetc.WasteproductsCO2AlcoholLacticacidetc.AlteredEnvironmentAlteredFoodMicrobialFoodSpoilageMicrobialgrowthintroducesal
11、terationsinfoodnappearancensmellnTastenNutritionalcontentChangesnotnecessarilyharmful!EachfooduniquemicrobialenvironmentnuniquespoilageagentsThreegroupsoffoods:baseduponrateofspoilagehighlyperishablenmeatnfruitnmilknvegetablesneggssemiperishablenpotatoesnnutsstablenricenflourndrybeansWhatdefineseach
12、group?AmountofwaterWETDryFoodSpoilageEachfoodhasitsownuniquemicrobialpopulationUncontrolledgrowthofthemicrobesresultsinfoodspoilageWecanpredict(andthereforecontrol)foodspoilageMilkspoilage(unpasteurised)Bacterialgrowthonmilksugarsn(Lactobacillus spp., Lactococcus spp.)pHreductionnlacticacidbuildup(b
13、ittertaste!)Changeinbacterialpopulationnfurther pH reductions and much morelactic acid, continues until all sugarsdepletedYeastsandmouldsdominatenuselacticacidforgrowth.pHrisenallowingfurtherbacterialgrowthBacteriauseproteinsasmajornutrientn(Primaryaminesproduced-Smelly!)Foodspoilagehasmajoreconomic
14、impactsMicrobialfoodspoilageFoods are characteristically spoiled by known organismsFoodSpoilageShapesHistoryNicholasAppertnaFrenchmanwhoinventedamethodtopreserveperishableorganicmaterials.nIn1809,Appertreceived12,000francsforhismethodofenclosingfoodinairtightjarswhichwerethenheated.nIn1810,Appertpub
15、lishedthefirstknownbookoncanningnboilingproductsinjarsforfourtosixhoursandthenpouringmoltenwaxoverthejars.nBythismethod,foodcouldbepreservedindefinitely.nUnfortunately,theglassjarsoftenbrokeontheirtriptothearmy!PreservationoffoodbykillingallmicrobesTemperaturencanningnsterilizationbyheatn121oCfor15m
16、inutesnallbacteriaandendosporeskilledPreservationoffoodbykillingallmicrobesRemovalorkillingofallmicrobesfromafoodwillpreventspoilage!n Removal or killing of all microbes from a food will drastically alter the foodtastetexturenutritional contentPreservationoffoodbypreventingmicrobialgrowthAnumberofpa
17、rameterscanbemanipulatedtoslow downmicrobialgrowthMoisturecontentwateractivity(Aw)PerishablefoodshaveahighAwnpreservebyloweringAwHowtoreducewater?dryingnsunnheatnfreeze-dried(expensive!)Howtoreducewater?additionofsaltorsugarnwaterneededtokeepsaltandsugarinsolutionPreservationoffoodbypreventingmicrob
18、ialgrowthpHHowtomakefoodacidic?nAddacide.g.aceticacidnAllowbacteriatomakeacidfromnaturalfoodcomponentsnlacticacidbacteriaPreservationoffoodbypreventingmicrobialgrowthTemperaturenstorageat4oCdegreesnrateofspoilagedecreasednstorageat-20oCdegreesnrateofspoilageextremelyslownneed-70oCtoeliminatespoilage
19、PreservationoffoodbypreventingmicrobialgrowthTemperaturenPasteurizationnmildheattreatmentnoverallmicrobialpopulationisreducednpathogensareeliminatedsincethesetendtobemoreheatsensitivethanotherorganisms.63Cfor30min.(batchpasteurization)72Cfor15sec.(flashpasteurization)FoodPreservationbycontrolofbacte
20、rialgrowthRadiationnuseofgammaraysfromCo60nmicrobeskilledbyfreeradicalsFoodcanbepackaged!NorecontaminationpossiblePasteurizationofmeat,poultry,cheeseNoalterationoffoodncontroversialclaimIrradiationiscontroversialIrradiationofvariousfoodsacceptedinUSandmanyothercountriesUKonlyallowsforirradiationofhe
21、rbs,spicesorvegetableseasoningsPreservationoffoodbypreventingmicrobialgrowthModifiedAtmospherePackagingnOxygennNitrogennCarbonDioxidenArgonMixdependsonfoodinquestionAlittleextramaterial.BBCRadio4Science“OntheshelfFoodSafetyThroughtheAgesDr.BillGriersonFoodPreservationsiteGoodlinkstorelatedmaterialFo
22、odStandardsAgencyGoodsiteforgeneralinformationFood Spoilage Tests- do not take these literallyTHE GAG TEST - Anything that makes you gag is spoiled (except for leftovers from what you cooked for yourself last night). Ditto for things that make you violently ill. EGGS - When something starts pecking
23、its way out of the shell, the egg is probably past its prime. Especially if the something is NOT a chicken. DAIRY PRODUCTS - Milk is spoiled when it starts to look like yogurt. Yogurt is spoiled when it starts to look like cottage cheese. Cottage cheese is spoiled when it starts to look like regular
24、 cheese. Regular cheese is nothing but spoiled milk anyway and cant get any more spoiled than it is already. Cheddar cheese is spoiled when you think it is blue cheese but you realize youve never purchased that kind. Blue cheese, by definition, is never spoiled. FROZEN FOODS - Frozen foods that have
25、 become an integral part of the defrosting problem in your freezer compartment will probably be spoiled - (or wrecked anyway) by the time you pry them out with a kitchen knife. EXPIRATION DATES - This is NOT a marketing ploy to encourage you to throw away perfectly good food so that youll spend more
26、 on groceries. Perhaps youd benefit by having a calender in your kitchen. MEAT - If opening the refrigerator door causes stray animals to congregate outside your house, the meat is spoiled. BREAD - Sesame seeds and Poppy seeds are the only officially acceptable spots that should be seen on the surfa
27、ce of any loaf of bread. Fuzzy and hairy looking white or green growth areas are a good indication that your bread has turned into a pharmaceutical laboratory experiment. FLOUR - Flour is spoiled when it wiggles. Food Spoilage Tests- do not take these literallyCEREAL - It is generally a good rule of
28、 thumb that cereal should be discarded when it is two years or longer beyond the expiration date. LETTUCE - Bibb lettuce is spoiled when you cant get it off the bottom of the vegetable crisper without Flash. Romaine lettuce is spoiled when it turns liquid. CANNED GOODS - Any canned goods that have b
29、ecome the size or shape of a baseball should be disposed of. Carefully. CARROTS - A carrot that you can tie in a clove hitch in is not fresh. RAISINS - Raisins should not be harder than your teeth. POTATOES - Fresh potatoes do not have roots, branches, or dense, leafy undergrowth. CHIP DIP - If you
30、can take it out of its container and bounce it on the floor, it has gone bad. EMPTY CONTAINERS - Putting empty containers back into the refrigerator is an old trick, but it only works if you live with someone or have a maid. UNMARKED ITEMS - You know it is well beyond prime when youre tempted to discard the Tupperware along with the food. Generally speaking, Tupperware containers should not burp when you open them. GENERAL RULE OF THUMB - Most food cannot be kept longer than the average life span of a hamster. Keep a hamster in or nearby your refrigerator to gauge this.
