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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
Ripening of the cheese leads to changes in
Texture, consistency, flavor
26
Some of the ripening is due to
The lactic acid bacteria, rennin or other enzymes present
27
Cheddar, swiss cheese and gouda are riped in
cheesecloth
28
Cheddar: ripening involves only
The lactic acid bacteria
29
Longer the ripening of cheddar, swiss and gouda, then
higher acidity and sharpness
30
WHat happens in swiss cheese during ripening
Propioibacteria produce propionic acid and acetic acid (flavor) and CO2 (bubbles)
31
cheddar, swiss and gouda are riped for
3-12 months
32
Oka is (bacteria, what is done to the cheese)
pressed curd is brined, surface washed frequently. Growth of Geotrichum
33
In blue cheese and ruquefort ripening happens mainly due to
The mold Penicillium roquefortii
34
How the blue cheese has its blue color
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)
35
For how long blue cheese and roquefort are ripened
3-6 months
36
Camembert is stored wrapped/unwrapped
Unwrapped
37
What bacteria are spread on the surface in the curd on camembert and brie
Mixture of mold(Penicillium) and bacteria (Brevibacterium)
38
Where the ripening of camembert and brie happens and for how long
Ripening in curing room (high humidity) 1-5 months
39
What is responsible for softening of the cheese in camembert and brie
Proteases
40
What is the precaution for camembert and brie
Good sanitary practices are required so that the cheese does not get contaminated
41
What is the must
Crushed grains of grapes
42
What is the purpose of metabisulfite (Na2S2O5)
to kill wild yeasts
43
What can be added to the must
sugar and organic acids depending on the final product
44
What cultures are used usually for wine making and why
S.cerevisiae and S.ellipsoideus, because they are resistant to metabisulfite and tolerate 12-14% alcohol
45
The difference between dry wine and sweet wine
Dry wine: all the sugar is fermented Sweet wine: some sugar is left or added after fermentation
46
What is the reaction for making vinegar
Ethanol->acetaldehyde->acetic acid
47
What is the conditions needed for acetic acid bacteria and what do they do
oxidize ethanol to acetic acid- strict aerobes ( not fermentation)
48
The difference between white wine and red wine
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
Why do we add metabisulfate
so we keep the same taste
50
the final electron acceptor in acetic bacteria is
oxygen
51
What bacteria is used in all commercial applications
Acetobacter
52
In the absence of acid acetobacter oxidize acetic acid to CO2 and water, so what is done to avoid it?
Some ethanol must remain to prevent this
53
What are two enzymes that are responsible for conversion of ethanol to acetic acid
alcohol dehydrogenase Aldehyde dehydrogenase
54
General process of making beer
1. Malting and mashing 2. Boiling 3. Fermentation
55
Explain how malting
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
What is mashing
Malt is then soaked in warm water (65C) for 1-2h-> mashing. The amylase degrades starch to fermentable sugars (glucose and maltose)
57
What is wort
When mash is filtered
58
What is done with the wort
Hops are added to the wort. Wort is boiled for 1-2 hours (near sterilization)
59
What is the purpose of hops
Gives flavor and bitterness. It has also antimicrobial properties and prevents lactic acid bacteria from growing in the final product
60
What is done after boiling wort for commercial beers
Filtered
61
At what temperature wort is cooled
20C
62
When fermentation to beer takes place
After cooling
63
What is added to the cooled beer mixture to make lager and what temperature
Lager : Saccharomyces carlsbergensis less fermentation (bottom yeasts-settle in the bottom, 6-12C)
64
What is added to the cooled beer mixture to make ale and what temperature
Saccharomyces cerevisisae (top yeasts, carried up by CO2 during fermentation , 14-23C)
65
What is polishing
Filtration, carbonation, pasteurization,etc.
66
What are light beers
Yeasts manipulated genetically so they can use all the sugars in the wort
67
What is the difference between distilled alcoholic beverages and beer
Different grains are added
68
What grain is added to vodka
wheat, rye or potatoes
69
What grain is added to gin
Grains+starchy product+juniper oil and other flavor ingredients
70
What is added to rum
Sugar cane (molasses)
71
What is added to brande/cognac
Wine
72
What is added to whiskies
malt brews (scotch) Corn in the US
73
What is done to alcohol?
It is distilled
74
After distillation process of alcohol drinks is finished what will be done to it
Aged, diluted with water ( if too strong) Flavor ingredients are added
75
How whisky is made
Word is not boiled, mixed fermentation of added yeasts and resident lactic acid bacteria
76
Factors affecting whiskies
- Water - Resident lactic acid bacteria - Source and cultivar of the barley - Shape of the still - Ageing in wood cask
77
What is kombucha
Fermented tea Can work with any tea, but black tea works best
78
How to make kombucha
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
What is added to SCOBY
Acetobacter and Saccharomyces
80
What is food spoilage
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
What is the percentage of spoilage in North america and in developing countries
10-20% in North america up to 50% in developing countries
82
Factors that affect food spoilage
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
All microorganisms need ___
water
84
Solutes dissolved in water reduce ____
Availability of water to microorganisms (vapor pressure decrease)
85
What is the difference between moisture content and water activity
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
What is the water activity in fresh food
Higher than 0.95
87
Most spoilage organisms can grow to an Aw as low as ___
0.9
88
What happens when Aw is smaller than 0.9
Most bacteria and yeasts are unable to grow. Many molds can still grow
89
Aw lower than 0.8. What can grow there
Xerophiles (dry environment, low osmolarity) Osmophiles (high osmolarity: high sugar) Halophiles (high salinity)
90
What organisms grow in Aw higher than 0.83
Staphylococcus aureus
91
Hot foods should be kept at temperature ___ to avoid spoilage
above 60C
92
Cold foods should be kept at temperature ___ to avoid spoilage
4.5C
93
What are psychrophiles and psychrotrophs
psychrophiles( grow best at low T) psychrotrophs ( able to grow at low T)
94
Most pathogens do not grow below 4.5C except
Yersinia enterocolitica Listeria monocytogenes Clostridium botulinum
95
What is the risky cycle
Freeze/Thaw cycle
96
Most foods are __ (pH)
Neutral or acidic
97
At what pH bacteria grow, lactic acid bacteria grow
Many grow at a pH as low as 5 Lactic acid bacteria at pH4 very few bacteria able to grow below pH 4
98
At what pH molds and yeasts grow,
Main spoilage organisms in acidic foods ( below pH of 4.5) Many can grow at pH4 and lower
99
Nutrients available will determine
the types of organisms that grow
100
What will determine the type of foods that the microorganisms can use
Enzymes produced and secreted
101
Meat is high in ___. What enzyme microorganisms need and what happens under anaerobic conditions
High in protein Requires proteases and lipases- proteolytic and lipolytic microorganisms: bacteria and molds Under anaerobic conditions: mostly bacteria
102
Vegetables are high in
Starch, cellulose, pectin
103
Fruits are high in ___
Sugars and pectin
104
Organisms thriving on vegetables and fruits need
Saccharase, cellulase, pectinase- saccharolytic, cellulytic and pectinolytic microorganisms (bacteria, yeasts , mold)
105
Oxygen is required for growth of what microorganisms?
For molds and many aerobic bacteria and yeasts
106
How to reduce spoilage with oxygen
Vacuum packaging Canning Modified atmosphere
107
What is the sign that it is better not to buy the package of vaccumed food
Swelling
108
Who can grow under anaerobic conditions
Some yeasts and many bacteria

Introductory Microbiology (21 decks)

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