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Microbiology > Chapter 18 > Flashcards

Chapter 18 Flashcards

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Biology 101 flashcards
1
Q

vinegar

A
  • Acetic acid bacteria oxidize ethanol to actic acid- strict aerobes, this is not fermentation
    • Ethanol = acetaldehyde=acetic acid
      ACETOBACTER: used in all commercial applications, very efficient but in the absence of alcohol, it will oxidize acetic acid to CO2 and H2O - some ethanol must remain to prevent this
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2
Q

brewing

A
  1. Sieved malt crushed and fet into Mash tun
    1. Crushed malt (grist) stirred in hot liquor to form a mash
    2. Mash sent into a copper and boiled with hops 60-90mins
    3. Spent hops collected from liquid
    4. Cooling
    5. Yeast added and fermentation takes place
    6. Ale is allowed to mature in conditioning tanks and placed into casks

** key factors: water, malt, hops, yeasts and condition of fermentation (temp,time)

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3
Q

malting and mashing

A
  • Grains contain starch that cannot be digested by yeasts
    • Grains (barley) are allowed to germinate, producing amylase = MALTING
    • The grains are then dried and crushed = MALT
    • Malt is then soaked in warm water (65C) for 1-2h = MASHING. The amylase degrades starch to fermentable sugars (glucose and maltose)
      The mash is then filtered = WORT
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4
Q

boiling

A
  • Hops is added to the wort. Wort is boiled for 1-2 hours (near sterilization)
    • Hops gives flavor and bitterness. It also has antimicrobial properties and prvents lactic acid bacteria from growing in the final product
    • Commercial beer= filtered
  • Cooled to 20C
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5
Q

fermentation

A
  • Yeast is added:
    1. Larger: saccharomyces carlsbergensis (bottom yeasts, 6-12C)
    2. Ale: saccharomyces cerevisiae (top yeasts, carried up by CO2 during fermentation, 14-23C)
      - Polishing: filtration, carbonation, pasteurization, …
      Light beers: yeasts manipulated genetically so they can use all the sugars in the wort
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6
Q

distilled alcohol beverages

A
  • Similar to beer making process but hops is not added. Different grains can be used:
    1. VODKA: wheat, rye or potatoes
    2. GIN: grains or starchy product + juniper oil and other flavor ingredients
    3. RUM: sugar cane (molasses)
    4. BRANDY/COGNAC: wine
    5. WHISKIES: malt brews
      - Alcohol is distilled
      - Aged, diltued with water
      Flavor ingredients are added
    • Whiskies: malt brew (scotch), other cereals (corn in the US). Wort is not boiled, mixed fermentation of added yeasts and resident lactic acid bacteria
    • Factors:
      1. Water
      2. Resident lactic acid bacteria
      3. Source of cultivar of the barley
      4. Shape of the still
      Ageing in wood cask
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7
Q

kombucha: fermented tea

A
  • Can be made with any type of tea (black tea tends to work best)
    • How to make Kombucha:
      1. Steep tea bags/leaves in boiling water
      2. Let cool to RT
      3. Strain tea/remove bags
      4. Add sugar
      5. And mother or SCOBY (symbiotic culture of bacteria and yeast)
    • Acetobacter and saccharomyces
      6. Transfer to jars and let ferment for 7-10 days
      Can add lots of extras for flavouring: herbs, spices, honey, fruit
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8
Q

food spoilage

A
  • Food spoilage: any change in the apperance, smell, taste that makes it unacceptable to the consumer. MAY still be safe to eat, not necessarily a health hazard
    • In north america, 10-20% of the foods are not suitable for consumption because of spoilage, up to 50% in developping countries
      Wide variety of microorganisms can cause spoilage: molds, yeasts, bacteria
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9
Q

factors that affect food spoilage

A
  • Types of microorganisms involved
    • Extent of growth of the microorganisms
    • Moisture content of the food
    • Temperature
    • pH
    • Availability of oxygen
    • Chemical composition and physical state
      Surfaces VS insides, grinding distributes the surface contaminant
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10
Q

moisture content

A
  • All microorganisms need water
    • Availability of water to microorganisms: water activity (aw)
    • Solutes dissolved in water reduce availability of water to microorganisms (vapor pressure decreases)
    • Fresh food: aw higher than 0.95
    • Aw of some foods:
      1. Maple syrup: 0.9
      2. Salted meats: 0.85
      3. Jams: 0.75
      4. Honey: 0.54
      5. Noodles: 0.5
      6. Cereal: 0.2
    • Moisture content: amount of bound water and free water in a sample, quantitative amount in a sample
      Water activity: amount of free water in a sample, a measurement of the energy status of the water in a system (qualitative)
    • Most spoilage microorganisms can grow to an aw as low as 0.9
    • Aw less than 0.9: most bacteria and yeasts are unable to grow. Many molds can still grow
    • Aw less than 0.8: only specialized organisms can grow:
      1. XEROPHILES (dry environement, low osmolarity)
      2. OSMOPHILES (high osmolarity: high sugar)
      3. HALOPHILES (high salinity)
      Staphylococcus aureus grows at aw high than 0.83
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11
Q

temperature

A
  • Crucial factor influencing spoilage
    • Hot foods should be kept above 60C
    • Cold food should be kept below 4,5C
    • Psycrophiles (grow best at low Temp)
    • Psychrotrophs (able to grow at low Temp)
    • Most pathogens do not grow at 4,5C except: YERSINIA ENTEROCOLITICA, LISTERIA MONOCYTOGENES, CLOSTRIDIUM BOTULINUM
      Microorganisms can survive for extended periods of time at 4C, if the temp. Is the temp. Is then allowed to increase, microorganisms can resume growth. (freeze/thaw cycle is risky)
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12
Q

pH

A
  • Most foods are neutral or acidic
    • Bacteria:
      1. Many grows at a pH as low as 5
      2. Lactic acid bacteria at pH 4
      3. Very few bacteria able to grow below pH 4
    • Molds and yeasts:
      1. Many can grow at pH 4 and lower
      Main spoilage organisms in acidic food (below pH of 4.5)
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13
Q

oxygen

A
  • Required for mols and many aerobic bacteria and yeasts
    • Excluding oxygen is a good sttrategy to prevent spoilage of food (vacuum packaging, canning, modified atmosphere). Also reduces oxidation of the product
      Some yeast and many bacteria can grow under anaerobic conditions; can cause swelling of the package (CO2 production): dont buy swollen packages!!
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14
Q

chemical composition

A
  • Nutrients available determine the types of organisms that grow
    • Enzymes produced and secreted will determine the type of foods that the microorgansims can use
    • Meat: high in proteins and fat. Requires proteases and lipases - proteolytic and lipolytic microorganisms: bacteria and mols. Under anaeroic conditions: mostly bacteria
      Vegetables: high in starch, cellulose, pectin, Fruits: high in sugars and pectin. Requires saccharase, cellulase, pectinase- saccharolytic, cellulolytic and pectinolytic microorganisms (bacteria, yeasts, molds)
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15
Q

effect of moisture on bacteria, yeasts, molds

A

High: molds, yeasts, bacteria
Low: molds, yeasts

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16
Q

effect of temperature on bacteria, yeasts, molds

A

Less than 10degree: molds, bacteria
Moderate: molds, yeast, bacteria
Higher than 40degree: only bacteria

17
Q

effect of acidity on bacteria, yeasts, molds

A 
High acidity (pH less than 4,5): molds and yeasts
Low acidity (pH highr than 4.5): yeast, molds, bacteria
18
Q

effect of oxygen on bacteria, yeasts, molds

A

Present: yeast, molds, bacteria
Absent: yeasts, bacteria

19
Q

effect of proteins, carbohydrates and fats on bacteria, yeasts, molds

A

Proteins: molds (+/-), bacteria
Carbohydrate: molds, yeasts, bacteria
Fat: molds, bacteria

20
Q

wine

A
  • Must= crushed grapes
    • Metabisulfite is added to kill wild yeasts
    • Sugar and organic acids may be added depending on the final product
      S. CEREVISIA + S. ELLIPSOIDEUS: rsistant to metabisulfite and tolerate 12-14% alcohol
      T. DRY WINE: all sugar is fermented
      SWEET WINE: some sugar is left or added after fermentation
21
Q

brie + camembert

A
  • Unwrapped
    • Mixture of mold (PENICILLIUM) and bacteria (BREVIBACTEIRUM) that are spread on the SURFACE of the curd
    • Ripening in curing room (high humidity)
    • 1-5 months
    • PROTEASES secretd by the microorganisms is responsible for the softening of the cheese
      Good sanitary practice = requires so cheese not contaminated
22
Q

blue and roquefort

A
  • Ripening is mainly du to the mold PENICILLIUM ROQUEFORTII
    • Spores from the mold are mixed with the milk (or the curd)
    • Small holes are drilled in the curd before wrapping
    • 3-6 months
      The mold grows in the holes and produces spores (blue)
23
Q

cheddar, swiss, gouda

A
  • Wrapped (cheescloth)
    • CHEDDAR: ripening involve LACTIC ACID BACTERIA only
    • Longer ripening = higher acidity and sharpness
    • SWISS = PROPIONIBACTERIA produce propinonic acid + acetic acid (flavor) and CO2 (bubbles)
      OKA: pressed curd is brine, surface is washed frequently, growth of GEOTRICHUM
24
Q

cheese - RIPENING

A
  • Ripening leads to changes in texture, consistency, and flavor
    • Due to specific microorganisms added with the starter culture or spread on the surface of the pressed curd
      Some of the ripening is due to the LACTIC ACID BACTERIA, RENNIN or other enzymes
25
Q

cheese - CURDLING

A
  • Starter cultures of lactic acid bacteria are added to the milk:
    1. Microorganisms ferment lactose, produce lactic acid
    2. Promote development of the curd (precipitated proteins, fat and other suspended material) and whey (supernatant)
      - Rennin (enzyme) can be added to the culture
    3. Cleaves casein which results in curd formation (rennin or lactic acid bacteria work)
      Whey is drained off: starting material for other processes (whey powder), or discarder (high BOD, must be treated like sewage)
      - Curd is then heated (temp. Depending on the final prodct): more whey is expelled and the crud becomes more solid
      - Salt may be added: flavor, promotes extraction of water, inhibits growth of spoilage organisms
      Packaging (fresh cheese), or other processes: pressing, brining, ripening
26
Q

milk products

A
  • Milk naturally contains lactic acid bacteria, but is usually pasteurized to remove potential pathogens. Desired microorganisms are then added back to give the final product
    1. YOGURT:
      - cultures of STREPTOCOCCUS THERMOPHILIS and LACTOBACILLUS BULGARIS are added and incubated at 42C
      - The acid denatures casein (milk protein) which results in thcikening
      - Other microorganisms are sometimes added (BL, BIFIBACTERIUM ANIMALIS)
    2. CHEESES: hundreds of microorganisms may be involved. Raw milk cheese may contain pathogens. 2 basic steps:
      - CURDLING: lactic acid bacteria precipitate the proteins = curd
      RIPENING: lactic acid bacteria + other microorganisms = flavor
27
Q

salami

A
  • Made with ground pork and or beef
    • Mixed with other ingredients:
      1. Salt, sugar, spices, yeast
      2. Sometimes a starter lactic acid bacterial culture is added
    • Mixture is added to casing and allowed to cure:
      1. The preservation of food by addition of salt and drying
    • Warm (25C), humid (95%), conditions for 1-3 days
      Transfert to cool (12-18C), and humid (70-80%_ conditions and dry sausages for 6-10 weeks
28
Q

sauerkraut and pickles

A
  • Cabbage is simply shredded and salted (final concentration of 2.2-2.8% NaCl, restricts growth of spoilage microorganisms). Microorganisms are naturally present on cabbage:
    1. LEUCONOSTOC MESENTEROIDES: lactic acid, flavor compunds, killed when acidity reaches 0.7-1%
    2. LACTOBACILLUS PLANTARUM: lactic acid only, increases acidity to 1.6-1.8%
    • PICKLES:
    • Use natural microflora
      Kill natural flora and use pure culture of PEDIOCOCCUS CEREVISIA and LACTOBACILLUS PLANTARYM (also sed to produce fermented sausages, salamie andbologna)
29
Q

most commons microorganisms

A
  1. LACTIC ACID BACTERIA: gram positive, aerotolerant anaerobes, rods or cocci
    • HOMOFERMENTATIVE: fermentation yields primarly lactic acid (pickles, sauerkraut)
    • HETEREOFERMENTATIVE: fermentation yields lactic acid AND a variety of flavorful compunds (fermented sugars such as salami, fermented milk products)
    • Lactic acid reduces food spoilage and improve storage qualitues (brings th pH down)
    • Flavor compunds produces by different organisms give each product its distinctive taste

YEASTS (alcohol beverages): variety of SACCHAROMYCES strains

Microbiology (25 decks)

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