Lab Exercise 12: Food Microbiology

Question 1

Define: homofermentative

Answer 1

organisms produce 1 fermentation product
(sugar→ lactic acid)
ex: saurkraut

Question 2

Define: heterofermentative

Answer 2

organisms produce MORE THAN 1 fermentation products
( sugar→ ethanol+ CO2 )
ex: apple cider

Question 3

What is fermentation?

o Does it require oxygen?

Answer 3

limits nutrients for spoilage & pathogenic organisms→ unsafe
-ANAEROBIC process to breakdown organic compounds to some waste products
-creates hostile environment for microbes
ex: ALCOHOL made by yeast to kill fungi & bacteria (wine &beer)
ACIDIS by bacteria to prevent growth of fungi & other bacteria (lactose →lactic acid/ maltose → alcohol & CO2)
-Adding microbes to change food product but not end product

Question 4

How come our root beer wasn’t “done” during class? What are we waiting for?

Answer 4

We are waiting for the yeast to ferment the apple juice and in doing that it releases ethyl alcohol + cardon dioxide

Question 5

What’s the difference between homemade root beer and what you buy in the store?

Question 6

Historically, why did people ferment milk (yogurt, cheese), cabbage (sauerkraut), fruit juice (wine)? What were they trying to prevent? (Be specific: “spoilage” is NOT an adequate answer)

Answer 6

People did not have refrigerators so this was done to prevent food from spoiling. It also changes the flavor of food, jalapenos, pickles, cabbage.

Question 7

Bromcresol purple - lactose agar:
o Name the key ingredients of this medium.
o What is the question we are asking about an organism with this medium?
o If you see an organism on this plate and the medium has turned yellow, what does this tell you about the organism’s physiology? What if it doesn’t turn yellow?

Answer 7

KEY INGREDIENTS: lactose, bromcresol purple (pH indicator)
? ASKED W/MEDIUM: Can the organism ferment lactose to acid?
RESULTS:
-Medium around colonies is PURPLE —organism cannot ferment lactose to acid (yogurt- heterofermentative)

-Medium around colonies is YELLOW —organism can ferment lactose to acid (buttermilk- homofermentative)

Question 8

Define fermentiated foods

Answer 8

microbes ferment food & are typically REMOVED from finished product (wine, beer)

Question 9

Define Cultured food

Answer 9

microbes ferment food & REMAIN in the finished product (Cheese, bread, pickle, suarkraut, salami, yogurt)