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Introductory Microbiology > Food microbiology > Flashcards

Food microbiology Flashcards

1
Q

Physical characteristics of lactic acid bacteria

A

Gram-positive, aerotolerant anaerobes

Rods or cocci

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2
Q

What are homofermentative

A

Fermentation yields primarily lactic acid ( pickles, sauerkraut)

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3
Q

What is heterofermentative

A

Fermentation yilds lactic acid and a variety of flavorful compounds (fermented sausages such as salami, fermented milk products)1

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4
Q

what does lactic acid do to food

A

Reduces food spoilage and improves storage qualities ( brings the pH down)

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5
Q

what strains of yeast are used for alcoholic beverages production

A

Variety of Saccharomyces strains

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6
Q

What is sauerkraut

A

Cabbage is simply shredded and salted

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7
Q

What is the final salt concentration of salt in sauerkraut

A

2.2-2.8%

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8
Q

Microorganisms naturally present on cabbage

A

Leuconostoc mesenteroides

Lactobacillus plantarum

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9
Q

what is the difference between Leuconostoc mesenteroides
AND
Lactobacillus plantarum

A

Leuconostoc mesenteroides produces lactic acid and flavor compounds and it is killed when acidity reaches 0.7-1%
Lactobacillus plantarum produces lactic acid only, increases acidity to 1.6-1.8%

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10
Q

What cultures are used for pickles

A
  • Natural

- Or sometimes the natural one is killed and use of pure culture of Pediococcus cerevisiae and Lactobacillus plantarum

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11
Q

pure culture of Pediococcus cerevisiae and Lactobacillus plantarum is also used for

A

Production of fermented sausages, salami, bologna

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12
Q

Salami: ingredients

A

Made with ground pork and/or beef

Mixed with other ingredients: salt, sugar, spices, yeast. Sometimes a starter lactic acid bacterial culture is added

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13
Q

How the salami is made after addition of all ingredients and how the preservation is made

A

Mixture is added to casing and allowed to cure

The preservation of food by the addition of salt and drying

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14
Q

What are the temperature and humid conditions for salami

A

Warm (25C), humid (95%) conditions for 1-3 days

Transfer to cool ( 12-18) and humid (70-80%) conditions and dry sausage for 6-10 weeks

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15
Q

Milk naturally contains ____, but it is usually removed by ___.

A

Lactic acid bacteria

Removed by pasteurization

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16
Q

To make yogurt what cultures are added and at what temperature

A

Streptococcus thermophilus and Lactobacillus bulgaris incubated at 42C

Other microorganisms are sometimes added ( BL, Bifidobacterium animalis)

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17
Q

What is happening in the yogurt with microorganisms

A

Streptococci produce some acids and favor the growth of Lactobacillus which produce most of the acid

The acid denatures casein which results in thickening

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18
Q

Two basic steps in cheese making

A

Curdling: lactic acid bacteria precipitate the proteins -> curd

Ripening: lactic acid bacteria+ other microorganisms -> flavor

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19
Q

Cheese production scheme

A

Raw milk->pasteurize->filtration-> inoculate organisms ->curdling-> remove the whey and mill the curd->addition of salt/herbs->addition of microorganisms if rippening

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20
Q

What is happening at cheese curdling step

A

Starter cultures of lactic acid bacteria are added to milk

  • Microorganisms ferment lactose, produce lactic acid
  • Promote development of the curd (precipitated proteins, fat and other suspended material) and whey (supernatant)
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21
Q

What is the function of rennin

A

Cleaves casein which results in curd formation ( rennin or lactic acid work)

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22
Q

In the end of curddling step what is done to the mixture

A

Whey is drained off: starting material for other processes (whey powder), or discarded (high BOD, must be treated like sewage)

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23
Q

After curd has been separated what happens

A

Curd is then heated: more whey expelled and the curd becomes more solid

Salt may be added: flavor, promotes extraction of water, inhibits growth of spoilage organisms

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24
Q

After salt is added what happens to the curd

A

Packaging (fresh cheese) , or other processes : pressing, brining, ripening

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25
Q

Ripening of the cheese leads to changes in

A

Texture, consistency, flavor

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26
Q

Some of the ripening is due to

A

The lactic acid bacteria, rennin or other enzymes present

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27
Q

Cheddar, swiss cheese and gouda are riped in

A

cheesecloth

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28
Q

Cheddar: ripening involves only

A

The lactic acid bacteria

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29
Q

Longer the ripening of cheddar, swiss and gouda, then

A

higher acidity and sharpness

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30
Q

WHat happens in swiss cheese during ripening

A

Propioibacteria produce propionic acid and acetic acid (flavor) and CO2 (bubbles)

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31
Q

cheddar, swiss and gouda are riped for

A

3-12 months

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32
Q

Oka is (bacteria, what is done to the cheese)

A

pressed curd is brined, surface washed frequently. Growth of Geotrichum

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33
Q

In blue cheese and ruquefort ripening happens mainly due to

A

The mold Penicillium roquefortii

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34
Q

How the blue cheese has its blue color

A

Spores from the mold are mixed with milk or the curd

Small holes are drilled in the curd before wrapping

The mold grows in the holes and produces spores (blue)

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35
Q

For how long blue cheese and roquefort are ripened

A

3-6 months

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36
Q

Camembert is stored wrapped/unwrapped

A

Unwrapped

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37
Q

What bacteria are spread on the surface in the curd on camembert and brie

A

Mixture of mold(Penicillium) and bacteria (Brevibacterium)

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38
Q

Where the ripening of camembert and brie happens and for how long

A

Ripening in curing room (high humidity)

1-5 months

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39
Q

What is responsible for softening of the cheese in camembert and brie

A

Proteases

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40
Q

What is the precaution for camembert and brie

A

Good sanitary practices are required so that the cheese does not get contaminated

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41
Q

What is the must

A

Crushed grains of grapes

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42
Q

What is the purpose of metabisulfite (Na2S2O5)

A

to kill wild yeasts

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43
Q

What can be added to the must

A

sugar and organic acids depending on the final product

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44
Q

What cultures are used usually for wine making and why

A

S.cerevisiae and S.ellipsoideus, because they are resistant to metabisulfite and tolerate 12-14% alcohol

45
Q

The difference between dry wine and sweet wine

A

Dry wine: all the sugar is fermented

Sweet wine: some sugar is left or added after fermentation

46
Q

What is the reaction for making vinegar

A

Ethanol->acetaldehyde->acetic acid

47
Q

What is the conditions needed for acetic acid bacteria and what do they do

A

oxidize ethanol to acetic acid- strict aerobes ( not fermentation)

48
Q

The difference between white wine and red wine

A

Juice sits with thee skin for some time, then it is removed and yeast are added

For red wine , yeasts are added right away to the juice and to the skin, so it gets the color

49
Q

Why do we add metabisulfate

A

so we keep the same taste

50
Q

the final electron acceptor in acetic bacteria is

A

oxygen

51
Q

What bacteria is used in all commercial applications

A

Acetobacter

52
Q

In the absence of acid acetobacter oxidize acetic acid to CO2 and water, so what is done to avoid it?

A

Some ethanol must remain to prevent this

53
Q

What are two enzymes that are responsible for conversion of ethanol to acetic acid

A

alcohol dehydrogenase

Aldehyde dehydrogenase

54
Q

General process of making beer

A
  1. Malting and mashing
  2. Boiling
  3. Fermentation
55
Q

Explain how malting

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

56
Q

What is mashing

A

Malt is then soaked in warm water (65C) for 1-2h-> mashing. The amylase degrades starch to fermentable sugars (glucose and maltose)

57
Q

What is wort

A

When mash is filtered

58
Q

What is done with the wort

A

Hops are added to the wort. Wort is boiled for 1-2 hours (near sterilization)

59
Q

What is the purpose of hops

A

Gives flavor and bitterness. It has also antimicrobial properties and prevents lactic acid bacteria from growing in the final product

60
Q

What is done after boiling wort for commercial beers

A

Filtered

61
Q

At what temperature wort is cooled

A

20C

62
Q

When fermentation to beer takes place

A

After cooling

63
Q

What is added to the cooled beer mixture to make lager and what temperature

A

Lager : Saccharomyces carlsbergensis less fermentation (bottom yeasts-settle in the bottom, 6-12C)

64
Q

What is added to the cooled beer mixture to make ale and what temperature

A

Saccharomyces cerevisisae (top yeasts, carried up by CO2 during fermentation , 14-23C)

65
Q

What is polishing

A

Filtration, carbonation, pasteurization,etc.

66
Q

What are light beers

A

Yeasts manipulated genetically so they can use all the sugars in the wort

67
Q

What is the difference between distilled alcoholic beverages and beer

A

Different grains are added

68
Q

What grain is added to vodka

A

wheat, rye or potatoes

69
Q

What grain is added to gin

A

Grains+starchy product+juniper oil and other flavor ingredients

70
Q

What is added to rum

A

Sugar cane (molasses)

71
Q

What is added to brande/cognac

A

Wine

72
Q

What is added to whiskies

A

malt brews (scotch)

Corn in the US

73
Q

What is done to alcohol?

A

It is distilled

74
Q

After distillation process of alcohol drinks is finished what will be done to it

A

Aged, diluted with water ( if too strong)

Flavor ingredients are added

75
Q

How whisky is made

A

Word is not boiled, mixed fermentation of added yeasts and resident lactic acid bacteria

76
Q

Factors affecting whiskies

A
  • Water
  • Resident lactic acid bacteria
  • Source and cultivar of the barley
  • Shape of the still
  • Ageing in wood cask
77
Q

What is kombucha

A

Fermented tea

Can work with any tea, but black tea works best

78
Q

How to make kombucha

A

Steep tea bags/leaves in boiling water

Let cool to RT

Strain tea/remove bags

Add dugar

And “Mother” or SCOBY (symbiotic culture of bacteria and yeast)

Transfer to jars and let ferment for 7-10 days

Can add lots of extras for flavouring: herbs, spices , honey, fruit

79
Q

What is added to SCOBY

A

Acetobacter and Saccharomyces

80
Q

What is food spoilage

A

Any change in the appearance , smell, taste that makes it unacceptable to the consumer. MAY still be safe to eat, not necessarily a health hazard

81
Q

What is the percentage of spoilage in North america and in developing countries

A

10-20% in North america

up to 50% in developing countries

82
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

83
Q

All microorganisms need ___

A

water

84
Q

Solutes dissolved in water reduce ____

A

Availability of water to microorganisms (vapor pressure decrease)

85
Q

What is the difference between moisture content and water activity

A

Moisture content: amount of “bound” water and “free” water in a sample. Quantitative mount of water in a sample

Water activity: amount of free water, availability of water to microorganisms

86
Q

What is the water activity in fresh food

A

Higher than 0.95

87
Q

Most spoilage organisms can grow to an Aw as low as ___

A

0.9

88
Q

What happens when Aw is smaller than 0.9

A

Most bacteria and yeasts are unable to grow. Many molds can still grow

89
Q

Aw lower than 0.8. What can grow there

A

Xerophiles (dry environment, low osmolarity)

Osmophiles (high osmolarity: high sugar)

Halophiles (high salinity)

90
Q

What organisms grow in Aw higher than 0.83

A

Staphylococcus aureus

91
Q

Hot foods should be kept at temperature ___ to avoid spoilage

A

above 60C

92
Q

Cold foods should be kept at temperature ___ to avoid spoilage

A

4.5C

93
Q

What are psychrophiles and psychrotrophs

A

psychrophiles( grow best at low T)

psychrotrophs ( able to grow at low T)

94
Q

Most pathogens do not grow below 4.5C except

A

Yersinia enterocolitica

Listeria monocytogenes

Clostridium botulinum

95
Q

What is the risky cycle

A

Freeze/Thaw cycle

96
Q

Most foods are __ (pH)

A

Neutral or acidic

97
Q

At what pH bacteria grow, lactic acid bacteria grow

A

Many grow at a pH as low as 5

Lactic acid bacteria at pH4

very few bacteria able to grow below pH 4

98
Q

At what pH molds and yeasts grow,

A

Main spoilage organisms in acidic foods ( below pH of 4.5)

Many can grow at pH4 and lower

99
Q

Nutrients available will determine

A

the types of organisms that grow

100
Q

What will determine the type of foods that the microorganisms can use

A

Enzymes produced and secreted

101
Q

Meat is high in ___. What enzyme microorganisms need and what happens under anaerobic conditions

A

High in protein

Requires proteases and lipases- proteolytic and lipolytic microorganisms: bacteria and molds

Under anaerobic conditions: mostly bacteria

102
Q

Vegetables are high in

A

Starch, cellulose, pectin

103
Q

Fruits are high in ___

A

Sugars and pectin

104
Q

Organisms thriving on vegetables and fruits need

A

Saccharase, cellulase, pectinase- saccharolytic, cellulytic and pectinolytic microorganisms (bacteria, yeasts , mold)

105
Q

Oxygen is required for growth of what microorganisms?

A

For molds and many aerobic bacteria and yeasts

106
Q

How to reduce spoilage with oxygen

A

Vacuum packaging
Canning
Modified atmosphere

107
Q

What is the sign that it is better not to buy the package of vaccumed food

A

Swelling

108
Q

Who can grow under anaerobic conditions

A

Some yeasts and many bacteria

Introductory Microbiology (21 decks)

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