Exercise 5-23 Micro Lab: Litmus Milk Medium
an undefined medium consisting of skim milk and the pH indicator azolitmin
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.
Azolitmin (litmus) is _____ at pH 4.5 and ________ at pH 8.3. Between those extremes it is ______
4 basic reactions occur in litmus milk:
1. lactose fermentation
2. reduction of litmus
3. casein coagulation
4. casein hydrolysis
the acid reaction usually begins with splitting the disaccharide into the monosaccharides ________ and ____________ by the enzyme ___________
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
reduced litmus is _______ and oxidized is __________
heavy gas production that breaks up the acid clot
converts the casein to para-casein to form the curd
these three enzymes coagulate casein and form a curd:
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
signs of a digestion reaction are what?
leaves a clear to brownish fluid behind
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