Exercise 5-23 Micro Lab: Litmus Milk Medium

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1

litmus milk

an undefined medium consisting of skim milk and the pH indicator azolitmin

2

Why is skim milk used in the litmus milk test?

skim milk provides nutrients for growth, lactose for fermentation, and protein in the form of casein.

3

Azolitmin (litmus) is _____ at pH 4.5 and ________ at pH 8.3. Between those extremes it is ______

pink
blue
light purple

4

4 basic reactions occur in litmus milk:

1. lactose fermentation
2. reduction of litmus
3. casein coagulation
4. casein hydrolysis

5

the acid reaction usually begins with splitting the disaccharide into the monosaccharides ________ and ____________ by the enzyme ___________

glucose
galactose
B-galactosidase

6

acid clot

accumulating acid may cause the casein to precipitate and form an acid clot which solidify the medium and can appear pink or white with a pink band at the top

7

reduced litmus is _______ and oxidized is __________

white
purple

8

stormy fermentation

heavy gas production that breaks up the acid clot

9

rennin

converts the casein to para-casein to form the curd

10

these three enzymes coagulate casein and form a curd:

1. rennin
2. pepsin
3. chymotrypsin

11

How does a curd differ from a clot?

it will not dissolve in alkaline conditions and tends to retract from the sides of the tube, revealing a straw colored fluid called whey

12

signs of a digestion reaction are what?

leaves a clear to brownish fluid behind

13

3 things litmus milk is designed to do:

1. differentiate Clostridium bacteria
2. differentiate Enterobacteracae from other gram negative bacilli
3. cultivate and maintain cultures of lactic acid bacteria