Lecture 39 - Food Microbiology

Question 1

How does water activity related to foodborne organisms?

Answer 1

The lower the water activity, the drier the food. Most bacteria cannot grow in this.

Question 2

What spoilage organisms survive best at water activity of 1? 0.9? 0.68?

Answer 2

1 (pure water): none
0.9: Cutoff for bacteria
0.68: xerophilic fungi

Question 3

What three methods can be used to reduce the water activity to preserve foods?

Answer 3

1. Salt curing
2. Sugar curing
3. Smoking

Question 4

What food properties can be altered to prevent spoilage?

Answer 4

1. Extreme pH (below 4.5 or above 9)
2. Extreme temperatures (below -20C or above 70C)
3. Oxygenation
4. Pathogen reduction treatments

Question 5

Why does freezing preserve food but not sterilize it?

Answer 5

It stops food from growing

Question 6

Name three food spoilage bacteria and where they can be found

Answer 6

1. Pseudomonas (wide metabolic ability)
2. Acetobacter (wine)
3. Lactic acid bact (dairy products)

Question 7

Name three food spoilage fungi and where they can be found

Answer 7

1. Aspergillus (grains)
2. Penicillium (many foods)
3. Rhizopus (bread)

Question 8

Name three bacterial toxins that produce food poisoning and where they can be found

Answer 8

1. Staph aureus (cream fillings, potato salad)
2. Bacillus cereus (rice and pasta)
3. Clostridium botulinum (improperly canned foods)

Question 9

Name 4 bacteria associated with foodborne infections and what foods

Answer 9

1. Salmonella (eggs, poultry)
2. Campylobacter (poultry, hot dogs)
3. Listeria (hot dogs, soft cheese)
4. E. coli (meats)

Question 10

What can we do to meet target rate for infection of foodborne pathogens?

Answer 10

report cases

Question 11

How do they make cheese?

Answer 11

1. Lactococcus cremoris and L. lactis added
2. Bacteria ferment lactose and make acid.
3. Proteins in the milk coagulates into curd, rennin catalyzes
4. Curd cooked, whey drained
5. Curds salted and pressed

Question 12

How do they make yogurt?

Answer 12

1. Streptococcus thermophilus, Lactobacillus bulgaricus added
2. Heat to 45C

Question 13

How do they make pickled vegetables?

Answer 13

1. Add vegetables to salt brine
2. Leuconostoc, Lactobacillus lower pH

Question 14

How do they make fermented sausage like pepperoni?

Answer 14

1. combine sausage with sugar, salt, and nitrate
2. Add Lactobacillus, Pediococcus
3. Ferment a few days
4. Smoke and dry

Question 15

How do they ferment fish?

Answer 15

1. Pack fish with 2% salt for 6 months
2. Haloanaerobium ferments

Question 16

How do they make beer?

Answer 16

1. Germinate grain (malt)
2. Enzymes release sugar (mash)
3. Drain mash liquid (wort)
4. Cool
5. Ferment
6. Bottle

Question 17

How do they make wine?

Answer 17

1. Fruit crushed to make must
2. Must is fermented by Saccharomyces cerevisiae
3. SO2 added to stop bacterial growth

Question 18

How do they use Acetobacter in a vinegar generator?

Answer 18

vinegar generator filters alcohol through wood chips, bacteria oxidize alcohol

Question 19

What products of fermentation are important in bread making?

Answer 19

gluten forms networks, CO2 is trapped

Question 20

How do they make soy sauce?

Answer 20

1. Soybeans and wheat cooked
2. Aspergillus fungi digests
3. Add to 18% salt brine