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67 Cards in this Set
- Front
- Back
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Food preservation
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food spoilage can cause a great economic loss and undesirable microbial growth can cause food poisoning
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techniques in food preservation that predate the science of microbiology
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salted, smoked or dried meat was found to last longer than fresh meat
keeping food in a cool place slowed spoilage souring helps to preserve foods |
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modern techniques that aid in food preservations
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sanitary handling: a clean plant, frequently sanitized equipment, clean hands, uniforms and hairnets, insect and rodent control reduces food contamination
rapid automated packaging that immediately follows cooking also helps improved sorting procedures pasteurization |
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primary food spoilage
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occurs in the field and is usually caused by insect infestations or moldy products
buyers and sorters usually deal with this problem by discarding adulterated commodities example: moldy tomatoes that are thrown away |
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secondary food spoilage
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occurs in the food processing plant or later
example: botulism grows in improperly canned food and toxins are produced while the food item is being stored. modern commercial canning procedures are primarily designed to kill all botulism spores. botulism spores are very tough so any procedure that effectively kills them will kill all other bacteria that are common causes of food poisoning |
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Biological sterilization
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means eliminating all living organisms from a given sample or environment
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commercial sterilization
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means freedom from Clostridium botulinum
the goal of commercial canning procedures is to ensure that a food product is free of the endospores from Clostridium botulinum, not necessarily free of all microbial life |
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Clostridium botulinum is important because:
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it produces an extremely potent neurotoxin
growns anaerobically at room temperature is fairly common in the soil produces endospores that are very resistant to heat a process that kills C. botulinum endospores will kill most microorganisms |
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Thermophillic bacteria
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more heat resistant than Clostridium
usually not a problem in food preservation because they don't grow at room temperature |
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4 steps of commercial canning
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1. blanching
2. exhausting 3. processing 4. product cooling |
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Step 1 of commercial canning: blanching
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exposure of the food to steam or hot wather softens food, sets the color, removes gummy substances, and inactivates enzymes in the food that cause it to "self destruct" when stored
blanching kills some microorganisms but that isn't the main goal |
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step 2 of commercial canning: exhausting
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removal of oxygen, creating anaerobic conditions
gets rid of or prevents growth of aerobic microorganisms |
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step 3 of commercial canning: processing
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exposing the product to temperatures above 100*C in a retort (a pressure cooker or autoclave)
the amount of time and the temperature of the processing step is influenced by the water content of the product and pH general goal is to use the minimal amount of heat necessary to kill all C. botulinum spores an acidic pH reduces heat resistance of most bacteria so foods with a low pH require less processing time than foods with a neutral pH |
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step 4 of commercial canning: product cooling
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the canned producted is cooled to prevent the growth of any thermophiles that may have survived the processing and to stop the heat from causeing the product to be overcooked
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3 types of canned food spoilage caused by thermoduric anaerobes
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flat-sour spoilage
swells sulfide-stinkers |
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flat-sour spoilage
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can doesn't budge, acid builds up in the product
usually caused by bacteria in the genus Bacillus that converts sugars to organic acids such as lactic acid |
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swells
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the ends of the can bulge du to the build up of gases such as CO2 and H2 that are produced by fermentative waste products by Clostridium species
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sulfide-stinkers
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caused by Clostridium species that makes H2S gas in the can
can might not swell because H2S is soluble in water H2S can react with iron ions from the product or the can and produces a black precipitate of FeS |
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Pasteurization
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form of heat treatment that kills certain pathogens or food spoilage organisms
object is to prevent the transmission of disease causeing germs or to prevent the rapid spoilage of product w/out damaging the product by overcooking it temperatures below 100*C are used not the same as sterilization in that it does not kill all microorganisms in product used to prolong shelf life of beer and to kill disease causing germs in fruit juices in wine production p. of grape juice kills undesirable microorg. before fermentation combo of past. then inoculating it with a starter culture helps to insurethe consisten production of good wine |
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pasteurization of milk
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63*C for 30 mins
72*C for atleast 15 secs lethal to Salmonella and mycobacterium tuberculosis and thus prevents transmission of salmonellosis and tuberculosis in milk |
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Freezing
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retards the growth of microorganisms and so prevents spoilage, but freezing does not kill most bacteria
it is important to cook or consume frozen foods soon after they are thawed |
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dehydration
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removal of water
bacteria cannot grow in a medium with low water activity drying meat and fruit is a very old way of slowing spoilage examples of dried food products: beef jerky, powdered milk, raisins, and powdered egg products are stable at room temperature for long periods of time a wide variety of foods can be preserved by freeze drying 2 common problems with dehydrated foods: 1.safe clean water is needed to rehydrate the food 2.some powdered foods may be difficult to dissolve |
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Chemical preservation to prevent food spoilage
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various chemicals that prevent the growth of microorganisms can be added to foods as long as these chemicals:
1.pose no danger to the consumer, and... 2.do not damage the taste of the product. high concentration of salt and sugar can inhibit microbial growth by reducing the water activity of the food some herbs naturally contain substances tha inhibit the growth of bacteria including: garlic, cloves, cinnamon, and oregano |
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food preservatives
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propionic acid
benzoic acid m-cresol butylated hydroxyanizole (BHA) butylated hydroxytolnene (BHT) |
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milk microbiology
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milk contains nutrients that can support the growth of many microorganisms
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milk contents
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protein (proteins are a good carbon and nitrogen source. the predominant protein in milk is called casein, there are also immunoglobulins)
carbohydrates (milk sugar, lactose, is a disaccharide: glucose+galactose) lipids (butterfat) vitamins (milk is naturally a source of B-vitamins, A and D may be added) minerals (esp calcium) trace elements water pH of about 7 isotonic salt concentration |
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sources of microorganisms that may contaminate milk
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feed and water that the cows get
bits of soil, dust, dirt and manure from the barn milking equipment may be heavily contaminated if not disinfected properly there are bacteria on the hide and udders of the cow humans that are handling the milk may introduce microorganisms |
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steps taken to fight microbial contamination of milk
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1.barn and milking equipment are kept as clean as possible, hoses, tanks, and cows' udders are regularly washed with disinfectant soln
this reduces the number of bacteria in the milk 2.milk is immediately cooled to 45*C to reduce growth of the bacteria in milk milk is kept refrigerated continually, except during pasterization 3. milk is pasteurized 4. milk is given an expiration date that accounts for the growth of microorganisms at refrigerated temperatures |
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procedures that can be used in the pasteurization of milk
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1. LTH--low temperature holding; milk is heated to 68.2*C for 30 minutes; aka LTLT--low temp, long time
2.HT--high temperature; milk is heated to 72*C for atleast 15 seconds; aka flash pasteurization 3.UHT--ultra high temperature; milk is heated to 149*C for a few seconds; 149*C is 300*F, which is well above boiling; sterilizes milk, so no refrigeration is needed until package is opened |
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disadvantages to UTH pasteurization
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some loss of nutrients, taste is affected and it is slightly more expensive than the other techniques
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History of milk pasteurization
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introduced in early 1900s to kill mycobacterium tuberculosis
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other common disease causing microorganisms that may contaminate milk:
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Coxiella burneti a common barnyard contaminant that causes Q-fever
Brucella abortus, causes Brucellosis Streptococcus pyogenes, which can lead to mastitis in the cown and scarlet fever in humans Salmonella typhi, typhoid fever Staphylococcus aureas, can cause skin infections and food poisoning Lysteria monocytogenes, causing lysteriosis |
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Tests that are commonly performed on raw and pasteurized milk
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standard plate count
breed smear methylene blue test phosphatase test |
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standard plate count
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used to measure the number of mesophilic bacteria, those that grow into visible colonies at 37*C in 40 hrs
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breed smear
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a microscopic examination used to check the presence of dust, dirt, and particles
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methylene blue test
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used to assess the number of respiring bacteria in milk
a fixed vol. of milk is added to a standard soln of methylene blue and the time required for the dye to be reduced to a colorless state is measured higher pops of bacteria result in a faster reduction of the dye |
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phosphatase test
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used to assess the effectiveness of a pasteurization procedure
this enzyme is found in raw milk, but is inactivated by heating Aspergillus (a fungus that produces tozins) and Coxiella (a bacterium that causes Q-fever) are killed by heat treatment that is sufficient to inactivate milk phosphatase |
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milk spoilage
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pasteurization slows milk spoilage and makes the milk safe to consume
most of the bacteria that can cause milk to spoil are killed by pasteurization, except for the thermoduric psychrophiles that cause slow putrification milk spoilage is a problem if the product gets contaminated after processing |
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types of milk spoilage
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acid production
gas production ropy fermentation protein digestion lipolytic alcoholic fermentation sweet curdlers |
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acid production in milk
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bacteria that incompletely oxidize milk sugar (lactose) procuce organic acids
lactic acid, it is considered to have a "clean" sour flavor this sort of fermentation is done deliberately using starter cultures to convert milk into yogurt or cheese when E. coli contaminates milk it produces a variety of acids that give and unpleasant sour taste |
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gas production in milk
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Clostridium, E. coli or yeasts may spoil milk through a process called "stormy fermentation"
these microorganisms produce acids and gass (mostly CO2 and some H2) the acide causes the milk protein casein to precipitate producing curds gas production within the curds causes them to float or be blown apart giving the spoiling milk a cloudy look |
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ropy fermentation in milk
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bacteria that produce capsular polysaccharides and grow in long chains or filaments cause the production of curds that are more stringy than lumpy
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protein digestion in milk
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bacteria that degrade the amino acids from the major milk protein casein produce bitter tasting "old" milk
many protein digesting bacteria are thermoduric psychrophiles, members of the genus Bacillus are common this type of spoilage is also called "putrification" |
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lipolytic spoilage in milk
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bacteria that break down lipids in the butter fat produce fatty acids and glycerol producing a flavor "rancid"
some pseudomonas and Staphylococcus bacteria and certain molds are lipolytic |
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alcohol fermentation in milk
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yeasts convert lactose to ethyl alcohol and CO2
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sweet curdlers in milk
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some microorganisms excrete an enzyme called rennit that causes a curd to form at a neutral pH
unfortunately this curdle formation is usually followed by proteolysis that leaves the milk bitter |
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cheese and yogurt production
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milk sugar s converted to lactic acid by bacterial fermentation
reduced pH causes precipitatino of the protein casein to form curds cheese making begins with pasteurized milk to eliminate undesirable microorganisms starter culters are added to the milk: for milk the bacteria used include: Streptococcus thermophilus and Lactobacillus bulgaricus; the incubation temperature is warm (43*C or 110*F) for cheese the starter culture depends on the desired product several species of lactic acid bacteria are used, most commonly: Lactococcus lactis for ripened cheeses, the curds are pressed to remove water and aged to allow the microorganism to continue producing flavorful compounds sharp cheddar cheese differs from milk cheddar because it is aged longer |
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beer production
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sugar from barley is converted to ethanol by yeast fermentation
malting: barley is moistened and allowed to germinate; enzymes in the seeds begin the process of breaking down starch to simple sugars mashing: malt and adjuncts are mixed with water to dissolve the sugars preparation for fermentation: spent grain is removed from the sugary liquid (wort); hops are added to the wort and the mixture is boiled fermentation: yeast starter culture is added to the wort; the culture is incubated for a while with air bubbled through the liquid to allow the yeast to grow rapidly; the air flow is shut off and the yeast must change over to anaerobic fermentative metabolism aging: kraeusening is a low temperature aging period used in larger production |
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general steps in sewage treatment
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primary treatment
secondary treatment chemical disinfection |
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primary treatment of sewage
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removal of coarse solids using screening, skimmers, grinders, and sediment in a settling tank provides mechanical removal of objects in the water
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secondary treatment of sewage
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digestion of solid and dissolved nutrients in the sewage by anaerobic and aerobic microorganisms (in 2 or more steps)
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chemical disinfection of sewage
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chemicals are added that kill pathogenic bacteria and solids are disposed of
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BOD - biochemical oxygen command
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is a measurement of the amount of oxygen that is used up by aerobic bacteria in a water sample in a 5 day period
high BOD caused by a high concentration of organic matter while a low BOD indicates a low concentration of organic matter goal of sewage treatment is to reduce the BOD, i.e. degrade the organic matter that is contaminating the waste water |
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Modern sewage treatment
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raw sewage is screened and pumped into a primary settling tank, particulates and flocs settle to the bottom forming the primary sludge
effluent is piped into a secondary treatment that promotes the degradation of organic compounds by aerobic microorg. in an activated sludge sys. the water is mixed w/ some recycled sludge from some earlier batch of sewage sludge is an active biomass of microorg. that grow on the nutrients in the sewage water is kept well oxygenated in a trickle filter sys. the effluent is passed over rocks that are covered w. a biofilm the microbial community in the mat degrades organic matter in the sewage much of the organic matter in the sewage is converted to CO2 microorg. are allowed to settle out as flocs; this removes organic matter from the water sludge from the primary treatment tank and trickle filter tank is put into an anaerobic digestion tank imhoff tank is an anaerobic environment, means that conditions are highly reduced bacteria and archaea in the imhoff tank break down organic matter and produce CO2 and methane methane is burned off or used for fuel effluent is chlorinated before it is released |
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indicator organisms
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tests for the presence of specific pathogens are very complicated and expensive
there are many diff pathogens that may contaminate drinking water and produce a risk to humans a test for a specific bacterium, such as Salmonella typhi, would do nothing to detect other types of disease causing microorganisms it is very difficult to culture and detect viral or protozoan pathogens instead water is tested for the presence of an INDICATOR organism presense of these bacteria in water is an indication that the water has been contaminated with fecal material presence of disease causing microorgs. in water is tightly linked to fecal contamination |
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examples of indicator organisms
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coliforms--small, gram negative bacteria that ferment lactose; non-spore forming, produce acid and gas in 24 hrs
coliform = similar to E. coli Enterococci--fecal Streptococci, small gram positive cocci found in the intestine |
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characteristics of the coliform bacteria
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always present in the large intestines and fecal materials of animals
in contaminated water, present in larger numbers than pathogenic bacteria generally survive in water longer than pathogenic bacteria easy to cultivate produce acid and gas from lactose in 24 hrs lactose fermentation on certain selective media is a presumptive identification of a coliform |
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true or false
there is generally high concentration of anaerobic bacteria in sewage |
true
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ture or false
raw sewage contains very little dissolved oxygen and is very anaerobic |
true
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true or false
anaerobic bacteria are used to degrade organic compounds in sewage |
true
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true or false
aerobic bacteria are used to degrand organic compounds in sewage |
true
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true or false
some of the bacteria found in raw sewage could cause human disease |
true
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true/false
wast products made by anaerobic bacteria contribute to the bad smell |
true
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true/false
a high concentration of bacteria in sewage causes it to have a high BOD |
true
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true/false
methanogenic achaea help to degrade organic matter in sewage |
true
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true/false
many microorgs. in a sewage treatment plant help to reduce BOD of the waste water by converting the organic compounds to CO2 , or methane anaerobically |
true
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biogeochemical cycle
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description of the conversion of an element from one form to another by living organisms and non-biological chemical reactions in the environment
these transformations typically involve redox reactions sulfur cycle nitrogen cylce carbon cycle |
