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Slide 1Food contaminationFermentationWineWine (II)CheeseBreadOther foodsCompetition between Microbes and Animals for FoodRole of Microbiologists in Food IndustryShelf life of foodSource of microbes that contaminate foodFactors that influence microbial growthConsequences of microbial action on foodSlide 15MeatsFishEggs, Milk, and DairySlide 19HeatPasteurizationOrganisms that survive pasteurizationMethods of PasteurizationLow temperatureOsmotic pressure and chemicalsRadiationMicrobes and AgricultureNitrogen FixationMicrobes and Beef ProductionMicrobes and Dairy ProductsMicrobes and Dairy ProductsBiotechnology and Microbes on the FarmIntroducing new genes into plantsSlide 34OverviewCarbon cycleSulfur cycleBiogeochemical Cycles (Cont.)Microbes and Waste Management: OverviewMicrobes and Waste ManagementSewage TreatmentSewage TreatmentDetection of Microbes in WaterBioremediationControl of MicrobesMoist Heat SterilizationDry Heat SterilizationFiltration & RadiationChemical Control of MicrobesAntimicrobial ChemotherapyMechanism of action of antibacterial drugsMetabolism of Antibiotic ResistanceOrigins of drug resistanceAntifungal drugs and AntiviralsMicrobes and Food3/17/14Food contamination•Food contamination with microbes does not always result in spoilage/disease•Microbes•Play important role in food production•Primarily via fermentation reactionsFermentation•Incomplete breakdown of carbs when oxygen is not present•Pyruvic acid: Plays central role•Microbes produce enzymes of fermentation•Microbial enzymes convert pyruvic acid to useful products secreted from cell•Controlled food spoilage  Culture specific•Alcohols, acids, other by-products give foods their unique qualities such as taste, aroma, texture•Ex: butter is composed of diacetyl and butryic acid•Ex: Swiss cheese is made of propionic acid•By-products also act as preservatives (acids) to prevent growth of dangerous and food spoilage microbesWine•Fermented fruit juice: Any fruit can be source•Most common microbe used is the budding yeast Saccharomyces•Often yeast cells are derived directly from the fruit; alternatively added from pure cultures •Fruit juice provides nutrients for growth of yeast (very rich in carbs)•Growth initially by aerobic respiration – CO2 produced from Krebs Cycle•As CO2 accumulates, anaerobic environment results and fermentation beginsWine (II)•Prolonged exposure to oxygen = Harmful to wine making•During fermentation, pyruvic acid from glycolysis is not directed to Krebs Cycle – instead converted to ethyl alcohol•When alcohol content reaches about 12% the yeast dies•Different varieties of wine depends on the•Source of the grapes•Strains of fermentation microbes•Presence/absence of stems and skin in crushed juice during fermentation distinguishes whether the wine will be red or wineCheese•Product of microbial fermentation of milk•Primarily effect on casein – the milk protein•Type of cheese results from •Microbe used in fermentation•Source of milk, etcBread•Flour (mostly from wheat) used as an energy source for yeast growth•Flour protein known as GLUTEN gives bread its spongy texture•Kneading introduces crosslinks between gluten molecules•Yeast sends pyruvic acid to both Krebs Cycle (hence CO2 production which causes bread to rise) and fermentation (ethanol produced is vaporized during baking)•Sour dough bread involves the use of lactobacillus to produce lactic acid and otherOther foods•Soy sauce•Fermentation of soybeans: Fungus Aspergillus•Beer•Fermentation of grain (barley, rice, rye): Saccharomyces species•Sake (from rice)•Technically a beer rather than wine•Aspergillus used for fermentation•Cocoa/Coffee•Fermentation of pulp surrounding beans, followed by drying or roastingCompetition between Microbes and Animals for Food•30% of food supply lost to spoilage = Microbial contamination •Foods contain nutrients and moisture to support microbial growth•Result: Uncontrolled fermentation•Food with little moisture will not support microbial growth•Dry foods keep wellRole of Microbiologists in Food Industry•Design protocols during preparation to prevent microbial contamination •Detect contamination before consumption (numbers and species)Shelf life of food•Depends on number of microbes initially present in food•Potato chips, dry pasta: long shelf life•Fish, milk: short shelf life•Acceptable to have some microbes in certain foods•Hamburger (less than 1000 staph/gram because it will be cooked)•Sliced ham: Most common source of staph food poisoning because staph are salt tolerant•Spoilage DOES NOT always result in sickness•Food decomposes and is not palatable•Microbial load of some food products is very HIGH•Yogurt and pickles•Not harmful, but actually beneficial•Even pasteurized milk has a high microbial loadSource of microbes that contaminate food•1) Air•2) Soil•3) Animals•4) Human handling•5) Water used for cleaning or in the habitat (ex: fish)Factors that influence microbial growth•1) Water content•2) ph•Fungi are LOW ph tolerant (acids)•3) Structure of food product•Ex: steak vs. hamburger•4) Oxygen•5) TemperatureConsequences of microbial action on food•Stench•Caused by hydrogen sulfide•Also due to CADAVERAE & PUTRACINE•Sour taste•Caused by acid fermentation•Gas production•Bloating of cans, killed animals•Pigment production•Red by Serratia •Blue-green by PseudomonasMicrobial action on food3/19/14Meats•Very susceptible to spoilage because they are a good source of nutrients•Cannot be pasteurized•Many opportunities for contamination during processing•Fecal bacteria•Contaminated cutting utensils•Exposure to moderate temperature•Ex: contaminated hamburger•Sliminess and brownish color indicate spoilage before smell does•Processed meats are especially susceptible due to frequent handling•Fermented meats such as hard sausage are less susceptible•Acidity inhibits growth of spoilage of microbesFish •Susceptible to spoilage even at low temperatures•Microbes on fish are psychrophiles•Filter feeders such as clams and mussels have a potentially high microbial load since they concentrate microbes in their systems•TRIMETHYLAMINE: Characteristic rotting fish smell•Derived from metabolic activity of marine bacteria on fish muscleEggs, Milk, and Dairy•Eggs•Mostly due to Salmonella contamination from GI tract of


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PSU MICRB 106 - Microbes and Food

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