(4) Food Microbiology Flashcards Preview

Introductory Microbiology > (4) Food Microbiology > Flashcards

Flashcards in (4) Food Microbiology Deck (28):
1

What are the two types of lactic acid bacteria used in food production and how do they differ?

Homofermentative: yields primarily lactic acid
Heterofermentative: yields lactic acid AND other flavorful compounds

2

What are the two most used microorganisms in food microbiology?

Lactic acid bacteria
Saccharomyces strands

3

How is yogurt produced, microbiologically speaking?

Lactic acid bacteria are incubated at 42°C and produce acid -> denatures casein -> thickens

4

What are the two basic roles of microorganisms when producing cheese?

Curdling: lactic acid bacteria and/or rennin precipitate proteins to make curd
Ripening: lactic acid bacteria w/ or w/o other organisms make flavor and texture change

5

How are the 5 different cheese ripened?

(lactic acid bacteria = LAB)
Cheddar = LAB
Swiss = LAB + propionibacteria
Oka = LAB + Geotrichum (surface)
Blue & Roquefort = Penicillium Roqueforti
Camambert & Brie = Penicilum + Brevibacterium (surface)

6

How is vinegar produced?

Not trough fermentation:
Acetobactor (strict aerobe) converts ethanol into acetic acid

7

In wine making, what is first added?

Metabisulfite -> to kill wild yeast present on grapes

8

How is red wine and white wine production different?

White wine: skin is removed
Red wine: skin is kept

9

How is dry wine and sweet wine production different?

Dry = no more sugar => all fermented
Sweet = not all fermented or added after full fermentation

10

What are the 6 steps in beermaking?

Malting: germinate grains -> produce amylase; obtain MALT
Mashing: soak malt in warm water -> amylases transform starch in maltose + glucose; Mash is filtered to obtain WORT
Hops (antimicrobial activity + flavor) added to wort
Boiling of wort (get virtually sterile)
Fermentation:
- S. carlsbergensis {carlsB for Bottom} = bottom yeast = Lager {bottom is Lower -> Lager}
- S. cervisiae = top yeast = Ale
Polishing (filter, add flavorings...)

11

How are distilled beverages produced?

Malting, Mashing, Fermenting, Distillation, Aging and/or Add flavors

12

How is Scotch whiskies production different than other distilles beverages?

The wort is not boiled; mixed fermentation done by LAB + yeasts

13

How can Food Spoilage be defined?

Any change making product unacceptable to the consumer

14

What microorganism (3) spoil foods?

Bacteria, molds & yeasts

15

What 6 factors affect food spoilage and their characteristics?

- Moisture content (water activity; if a-w <0.9, most are -inhibited; if a-w <0.8, only specialized organisms survive)
- Temperature (hot > 60°C, cold <4.5°C; prevents further growth)
- pH (molds and yeast can survive below 4.5, bacteria cannot)
- Oxygen availability (required for molds)
- Chemical composition (proteins & fat not accessed by yeasts)
- Surface Vs. Inside

16

What are the 3 specialized organisms that can survive in low water activity?

Xerophiles (dry env.)
Osmophiles (high osmolarity {sugar})
Halophule (high salt)

17

How does food poisoning/intoxication differs from food infection?

Poisoning/intoxication = caused by toxins => symptoms appear quickly
Infection = organisms ingested infect host => delayed symptoms

18

Describe two examples of food poisoning/intoxication

Botulism: botulinum toxin is heat-labile (80°C for 10 min), spores are not (dangerous only to infants)
Staphylococcus aureus: carried by humans -> food contamination -> exotoxin (Vs. endo) affecting intestinal cells = enterotoxin

19

Describe two examples of food infection

Salmonella enterica: infects and grows in intestinal cells. Killed by cooking
E. Coli O157:H7 produces AB-type (shiga-like toxin) once in intestinal cells. If toxin enters bloodstream, may damage kidney cells (hemolytic uremic syndrome). Killed by cooking

20

What are the 3 main goals of food preservation?

Prevent/delay decomposition by microorganisms
Destroy pathogens or inhibit their growth
Prevent/delay self decomposition by enzymes in food

21

What are 6 food preservation techniques?

- Refrigerating & Freezing: slows growth, freezing reduces water activity
- Pasteurization: reduce number of microorganisms
- Canning: 100°C for acidic; 121°C for low-acid
- Water availability:
a) drying
c) lyophilisation
c) addition of salt/sugar
- Irradiation: protects food's surface
- Chemicals: control growth microorganisms with Generally Recognized as Safe (GRAS)

22

What are 3 pasteurization methods for milk?

Long Time Low Temp: 30min, 62.8°C
High Temp Short Time: 15 sec, 71.2°C
Ultrahigh temperature: 2 sec, 141°C (virtually sterile)

23

In canning, what is the 12D process?

Norm by which if kill 10^12 botulinum spores, consider product sterile

24

What are 3 GRAS chemicals?

Nitrite -> C. botulinum
Sulfites -> wild yeast
Nisin (produced by lactococcus lactis {cheese})

25

What are primary metabolites?

Metabolites produced during exponential growth (alcohol)

26

What are secondary metabolites?

Metabolites produced near the stationary phase (end of growth) -> antibiotics

27

In industrial microbiology, what is considered fermentation?

Any microbiological process (aerobic or anaerobic)

28

What two types of organism variation can be used in industrial microbiology?

Spontaneous mutants: overproduce desired metabolites
Genetically modified organisms: cloned genes expressed in bacteria/yeasts