Lab Manual: Litmus Milk reactions

Helpfulness: -1
Set Details Share
created 10 years ago by jenkarmata
1,429 views
Microbiology 205 lab manual tests Fall 2012
updated 10 years ago by jenkarmata
Grade levels:
College: Second year
show moreless
Page to share:
Embed this setcancel
COPY
code changes based on your size selection
Size:
X
Show:
1

What is lactose?

A milk sugar

2

What are the 3 milk proteins?

1. Casein
2. Lactalbumin
3. Lactoglobulin

3

The major milk substrates capable of transformation are the

1. milk sugar- lactose
&
2. the 3 milk proteins: casein, lactalbumin & lactoglobulin.

4

Why is litmus incorporated into the medium?

To distinguish among the metabolic changes produced in milk.

5

Litmus is an

oxidation reduction indicator.

6

Litmus milk now forms an excellent differential medium in which microorganisms can

metabolize milk substrates depending on their enzymatic complement.

7

______ ____ now forms an excellent differential medium in which microorganisms can metabolize milk substrates depending on their enzymatic complement.

Litmus milk

8

~LACTOSE FERMENTATION~
Organisms capable of using __a____ as a carbon source for energy production utilize the inducible enzyme __________b__________.

a. lactose
b. ßglalctosidase

9

~LACTOSE FERMENTATION~
Organisms capable of using lactose as a carbon source for energy production utilize the inducible enzyme ß-galactosidase and degrade lactose as follows:

Lactose → ßgalactosidase→ GLUCOSE+ GALACTOSE
↓Embden-Meyerhof pathway
Pyruvic acid

Lactic acid

10

~GAS FORMATION~
The end products of microbial fermentation of lactose are likely to include the gases

CO2↑(carbon dioxide)+H2↑(hydrogen peroxide).

11

~GAS FORMATION~
The presence of gas may be seen as

separations of the curd or by the development of tracks or fissures within the curd AS GAS RISES TO THE SURFACE.

12

~LITMUS REDUCTION~
_________ is an anaerobic process involving biooxidations that occur in the absence of molecular oxygen.

Fermentation

13

~LITMUS REDUCTION~
_______ ___ cannot exist in the free state, there
must be an immediate & concomitant electron acceptor available to bind these hydrogen ions, or else oxidation reduction reactions are not possible & cells cannot manufacture energy.

Hydrogen ions

14

~LITMUS REDUCTION~
In the litmus milk test, _____ acts as such an acceptor.

litmus

15

While in the oxidized state, the litmus is _____ (what color)

purple

16

When the litmus accepts hydrogen from a substrate, it will become REDUCED & turn ____ or ____ colored.

white / milk

17

Definition of oxidized

1. To combine with oxygen; make into an oxide.
2. To increase the positive charge or valence of (an element) by REMOVING electrons

18

Oxidation of lactose, which produces _____ ___, butyric acid CO2↑ & H2↑ is as follows:
Lactose→Glucose→Pyruvic acid→Lactic acid
→Butyric acid
→CO2 + H2

lactic acid

19

~CURD FORMATION~
There are 2 distinct types of curds. What are they

1- acid
2-rennet

20

~CURD FORMATION~
Acid curd

Lactic acid or other organic acids precipitation of milk protein caseinas CALCIUM CASEINATE to form an insoluble clot. THE CLOT IS HARD & WILL NOT RETRACT FROM THE WALL OF THE TEST TUBE.

21

Acid curds are

hard & will not retract from walls of test tube.

22

~CURD FORMATION~
Rennet curd

Some organisms produce rennin, an enzyme that acts on casein to form paracasein, which in the presence of calcium ions is converted to calcium paracaseinate & forms an insoluble clot. Unlike acid curd, THIS IS A SOFT SEMISOLID CLOT THAT WILL FLOW SLOWLY WHEN THE TUBE IS TILTED.

23

Which curd is known to be soft & semisolid and will flow slowly if tube is tilted?

Rennet curd

24

Which curd is known to be hard and not retract from tube walls?

Acid curd

25

~Proteolysis (Peptioniztion)~
The inability of some microorganisms to obtain their energy by way of lactose fermentation means they must use other nutritional sources such as ______ for this purpose.

proteins

26

~Proteolysis (Peptioniztion)~
By means of proteolytic enzymes, these organisms __a___ the milk protein, primarily casein, into their basic building blocks, namely __b_______.

a. hydrolyze
b. amino acids

27

~Proteolysis (Peptioniztion)~
Hydorlyizng milk proteins into amino acids is accompanied by the evolution of __________________, resulting in alkaline pH in the medium

large quantities of ammonia

28

~Proteolysis (Peptioniztion)~
Large quantities of ammonia resulting in alkaline pH in the medium turns the litmus to a _________ color in the upper portion of the tube, while the medium begins to lose body & produces a translucent, brown, wheylike appearance as the protein is hydrolyzed to amino acids.

deep purple

29

~ALKALINE REACTION~
An alkaline reaction is evident when the color of the medium

remains unchanged or changes to a deeper blue.

30

When the medium remains unchanged or turns deep blue, that reaction is indicative of the

partial degradation of CASEIN into SHORTER POLYPEPTIDE CHAINS.

31

Litmus milk reactions image

card image

Control= uninoculated
The far right (very last one) is proteolysis