3 Food Microbiology28-1 Describe thermophilic anaerobic spoilage and flat sour spoilage by mesophilic bacteria.28-2 Compare and contrast food preservation by industrial food canning, aseptic packaging, radiation, and high pressure.28-3 Name four beneficial activities of microorganisms.
4 Historically…DryingOsmotic pressure (salt or sugar)Fermentation
5 Foods and Disease Hazard Analysis and Critical Control Point (HACCP) FDAUSDA
6 Washing, sorting, blanching Figure 28.1 The commercial sterilization process in industrial canning.Blanching in hot water or steam softens the product to easily fill the can.Washing, sorting, blanchingSteam boxThis treatment lowers the microbial population and destroys enzymes that might alter color, flavor, or texture.Cans are filled to capacity, leaving minimal dead space.Steam is used to exhaust, or drive out, dissolved air.The cans are sealed.Cans are sterilized by pressurized steam in a retort, similar to an autoclave.Cans are then cooled by submersion in a water bath or by spraying them with water.Cans are labeled, stored, and delivered for sale.
15 Irradiation sources lifted from storage pool for processing period Figure 28.6 A gamma-ray irradiation facility.Irradiation sources lifted from storage pool for processing periodShieldingMaterial to be irradiatedShieldingConveyors to move material in and out of processing positionThe irradiation source is submerged in the storage pool. The blue glow is Cerenkov radiation caused by charged particles exceeding the speed of light in water.An irradiation facility, showing the path of the material to be irradiated
17 High Pressure Prewrapped, precooked foods 87,000 psi Kills Salmonella, Listeria, E. coliPreserves color and flavor well
18 Cheese Curd: solid casein from lactic acid bacteria and rennin Whey: liquid separated from curdHard cheeses are produced by lactic acid bacteriaSemisoft cheeses are ripened by Penicillium on surface
19 Figure 28.8 Making cheddar cheese. The milk has been coagulated by the action of rennin (forming curd) and is inoculated with ripening bacteria for flavor and acidity. Here the workers are cutting the curd into slabs.The curd is chopped into small cubes to facilitate efficient draining of whey.The curd is milled to allow even more drainage of whey and is compressed into blocks for extended ripening. The longer the ripening, the more acidic (sharper) the cheese.
20 Figure 28.9 The basic steps in making red wine. Grapes are tested and picked.Sulfite is added to kill undesirable yeasts and bacteria.Yeast inoculum is added.Result is pressed to separate solids from wine.Wine is clarified in settling vats.Fermentation occurs.Grapes are crushed and destemmed.Wine is filtered.Wine is aged.Wine is bottled.
21 Alcoholic Beverages and Vinegar Beer and ale are fermented starchMalting: germinating barley converts starch to maltose and glucoseFor sake, rice starch is converted to sugar by AspergillusWine is fermented plant sugarsYeast ferment sugars to ethanol and CO2Grape wine requires bacterial malolactic fermentationAcetobacter and Gluconobacter convert ethanol to acetic acid
22 Microbial Metabolism Sugar Ethanol + CO2 Malic acid Lactic acid Saccharomyces cerevisiaeMalic acidLactic acidLactic acid bacteriaEthanolAcetic acidAcetobacter or Gluconobacter
23 Is botulism a greater danger in spoilage of canned goods under thermophilic or under mesophilic conditions? 28-1Canned foods are usually in metal cans. What sorts of containers are used for aseptically packaged foods? 28-2Roquefort and blue cheeses are characterized by blue-green clumps. What are these? 28-3
24 Industrial Microbiology 28-4 Define industrial fermentation and bioreactor.28-5 Differentiate primary from secondary metabolites.28-6 Describe the role of microorganisms in the production of industrial chemicals and pharmaceuticals.28-7 Define bioconversion, and list its advantages.28-8 List biofuels that can be made by microorganisms.
25 BiotechnologyUse of microorganisms, cells, or cell components to make a productClassical: fermentationRecombinant DNA
26 Section of a continuously stirred bioreactor Figure 28.10a Bioreactors for industrial fermentations.Acid/basefor pH controlMotorSteam for sterilizationFoam breakerLiquid levelFlat-bladed impellerCulture brothBaffleCooling jacketDiffuserSterile airHarvesting drainSection of a continuously stirred bioreactor
27 Bioreactor tank, at left Figure 28.10b Bioreactors for industrial fermentations.Bioreactor tank, at left
28 Cells Ethanol produced Cell weight or numbers Time Figure 28.11a Primary and secondary fermentation.CellsEthanol producedCell weight or numbersTime(a) A primary metabolite, such as ethanol from yeast, has a production curve that lags only slightly behind the line showing cell growth.
29 Tropophase Idiophase Cells Cell weight or numbers Penicillin produced Figure 28.11b Primary and secondary fermentation.TropophaseIdiophaseCellsCell weight or numbersPenicillinproducedTime(b) A secondary metabolite, such as penicillin from mold, begins to be produced only after the logarithmic growth phase of the cell (tropophase) is completed. The main production of the secondary metabolite occurs during the stationary phase of cell growth (idiophase).
33 Figure 28.14 Biological leaching of copper ores. Leaching: Fe3+ in acidic leaching solution oxidizes insoluble copper sulfide (Cu+) to soluble CuSO4 (Cu2+).Pregnant(metal-bearing)solution, CuSO4Copper for industrial usesLeach dump ofcopper sulfide oreFe0 (metallic scrap iron)PumpOxygen in aerated pondOxidation pond:T.Ferrooxidans oxidizes FeSO4 to Fe3+ + H2SO4 (acidic leaching solution).Barren solution,no copper, ironas FeSO4CuSO4 precipitates as copper (Cu0); Fe3+ is changed to FeSO4 (Fe2+).
34 Alternative Energy Sources Using Microbes Cellulose digested by cellulaseSugars fermented to ethanol or higher alcohols or hydrogenAlgal oilsBiomassMethaneEthanolHydrogenBioconversion
35 Microturbines produce electricity from methane Figure Methane production from solid wastes in landfills.Gas flaring stacksMicroturbines produce electricity from methane
36 Industrial Microbiology and the Future Food processingPharmaceuticals from rDNA technologyEthanol and hydrogenAnd more
37 Are bioreactors designed to operate aerobically or anaerobically? 28-4 Penicillin is produced in its greatest quantities during the trophophase of fermentation. Does that make it a primary or secondary metabolite? 28-5At one time, citric acid was extracted on an industrial scale from lemons and other citrus fruits. What organism is used to produce it today? 28-6
38 Landfills are the site of a major form of bioconversion—what is the product? 28-7 How can microbes provide fuels for cars and electricity? 28-8