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LSCI 230: Microbiology > Food Microbiology > Flashcards

Food Microbiology Flashcards

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1
Q

What microorganisms are most invovled in fermented food products

A
  • Lactic acid bacteria
  • Variety of yeasts
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2
Q

Homofermentative

A

Fermentation yields:
* Primarily lactic acid

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3
Q

Heterofermentative

A

Fermentation yields
* Lactic acid
* Variety of flavorful
compounds

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4
Q

Function of lactic acid

A

Reduces food spoilage and improves storage qualities

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5
Q

Function of flavorful compounds

A

Give each product its distinctive
taste

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6
Q

Lactic acid bacteria: Description

A

Gram-positive, aerotolerant anaerobes, rods or cocci

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7
Q

Milk products

A
  • Contains lactic acid bacteria but is usually pasteurized to remove potential pathogens.
  • Desired microorganisms are then added back to give the final product
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8
Q

Yogurt

A

Cultures of Streptococcus thermophilus and Lactobacillus bulgaris are added & incubated at 42°C
* Streptococci produce some acids & favor the growth of Lactobacillus
* Lactobacillus produce most of the acid
* The acid denatures casein (milk protein) which results in thickening

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9
Q

Cheeses

A

2 basic roles:
* Curdling
* Ripening

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10
Q

Cheese Curdling: Process

A
  • LAB ferment lactose and produce lactic acid
  • Rennin cleaves casein
  • Whey is drained off (disposed of)
  • Curd is heated
  • Salt may be added to add flavor and promotes extraction of water which inhibits growth of spoilage organisms
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11
Q

Cheese ripening: Result

A

Ripening leads to changes in texture, consistency, and flavor

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12
Q

Ripening: Cheddar, Swiss, Gouda

A

Cheddar:
- Involves the LAB only

Swiss:
- propionibacteria produce propionic acid & acetic acid (flavor), & CO2

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13
Q

Ripening: Blue and roquefort

A

Penicillium roquefortii
* Spores are mixed with the milk
* Small holes are drilled in the curd
* The mold grows in the holes & produces spores (blue)

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14
Q

Ripening: Camember, Brie

A

Mixture of mold (Penicillium) and bacteria (Brevibacterium)
* Proteases secreted by the microorganisms is responsible for softening of the cheese.

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15
Q

Wine

A

Consists of:
* crushed grapes
* S. cerevisiae
* S. ellipsoideus

Metabisulfite is added to kill wild yeasts
* S. cerevisiae and S. ellipsoideus are resistant to Metabisulfite and tolerate 12-14% alcohol

Sugar and organic acids may be added
depending on the final product

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16
Q

Dry wine

A

All the sugar is fermented

17
Q

Sweet wine

A

Some sugar is left or added
after fermentation.

18
Q

Brewing: Process

A
  • Malting and mashing
  • Boiling
  • Fermentation
19
Q

Malting and mashing

A

Malting:
* Grains (barley) are allowed to germinate, producing amylase

Malt:
* The grains are then dried and crushed

Mashing:
* Malt is then soaked in warm water (65°C) for 1-2h
* The amylase degrades starch to fermentable sugars

Wort:
* The mash is then filtered

20
Q

Boiling

A
  • Hops is added to the wort
  • Wort is boiled for 1-2 hours
21
Q

Hops

A
  • Gives flavor and bitterness
  • Has antimicrobial properties and prevents LAB from growing in the final product
22
Q

Fermentation

A

Yeast is added
* Lager: Saccharomyces carlsbergensis
* Ale: Saccharomyces cerevisisae

Polishing: filtration, carbonation, pasteurization…

23
Q

Distilled alcoholic beverages

A

Similar to the brewing making process but hops is not added

23
Q

Vinegar

A

Acetic acid bacteria oxidize ethanol to acetic acid
* strict aerobes, this is not fermentation.

24
Q

Acetobacter

A
  • Used in all commercial applications
  • Very efficient but in the absence of ethanol, it will oxidize acetic acid to CO2 & H2O
  • some ethanol must remain to prevent this
25
Q

Food spoilage

A

Any change in the appearance, smell, taste that makes it unacceptable to the consumer.

26
Q

Factors affecting spoilage

A
  • Moisture content of the food
  • Temperature.
  • pH.
  • Availability of oxygen.
  • Chemical composition
27
Q

Moisture content

A
  • All microorganisms need water
  • Solutes dissolved in water reduce availability of water to microorganisms
  • a w < 0.9 : most bacteria and yeasts are unable to grow
  • a w < 0.8 : only specialized organisms can grow
28
Q

Temperature

A

Hot foods should be kept above 60°C

Cold food should be kept below 4.5°C

29
Q

pH

A

Most foods are neutral or acidic

Bacteria:
* Many grow at a pH as low as 5.
* LAB at pH 4
* Very few bacteria able to grow below pH 4

Molds and yeasts:
* Many can grow at pH 4 and lower.
* Main spoilage organisms in acidic food

30
Q

Oxygen

A
  • Required for molds and many aerobic bacteria and yeasts
31
Q

Chemical composition

A
  • Nutrients available determine the types of organisms that grow

Meat:
* high in proteins and fat
* Requires proteolytic and lipolytic microorganisms

Vegetables and fruits
* high in starch, cellulose, pectin
* Require saccharolytic, cellulolytic and pectinolytic microorganisms

LSCI 230: Microbiology (14 decks)

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