milk microbiology

Question 1

PR O DUCTS O F
MICR O BIAL
GR OWTH

Answer 1

Enzymes (hydrolytic enzymes)
Decomposition products (fats, proteins, sugar)
Pigments
Toxins
Miscellanous changes

Question 2

S O URCES O F
C O NTAMINATI O N

Answer 2

Soil, water, plant
Feed - contains more than 10^8 psychrotrophs
Water - rinse animals and equipment
Animal - udder & teat canal, hide, hooves
(commensal microflora)
Milking parlour
Floors

Question 3

Results of microbial growth in milk

Answer 3

Proteolysis, ropiness, sweet curdling, aroma production, colour change and souring

Question 4

Types of microorganisms in milk

Answer 4

Bacteria, yeast, mold and bacteriophage

Question 5

PREDOMINANT SPOILAGE BACTERIA IN MILK

Answer 5

Pseudomonas, LAB, Coliform

Question 6

MICROBIAL ENZYMES RESPONSIBLE FOR SPOILAGE: protease

Answer 6

-Associated with bitterness in milk, Gelation of UHT sterilized milk, the reduced yield of soft cheese
-Most proteases able to degrade caseins

Question 7

MICROBIAL ENZYMES RESPONSIBLE FOR SPOILAGE: lipase

Answer 7

-Produce flavour defects by hydrolyzing
triglycerides associated with fat breakdown in cream, butter, cheese and UHT products
-Pseudomonas primary concern with regard to lipolytic degradation of milk

Question 8

Control of microbial spoilage of milk 3P2RC

Answer 8

Prevent contamination
Rapid cooling
Refrigeration
Cleaning & sanitising
Pasteurisation
Prevent recontamination of pasteurised products

Question 9

LTLT

Answer 9

Low temp long time 63-65C for 30 mins, vegetative pathogens

Question 10

HTST

Answer 10

High temp short time 72C for 15-30s, vegetative pathogens

Question 11

UHT

Answer 11

Ultra high temperature 130-135C for 1s, all microbes

Question 12

Pasteurization:

Answer 12

Surviving organisms are spore formers, thermoduric and
thermophilic organisms

Question 13

Souring

Answer 13

Lactobacillus sp.
Streptococcus sp.

Question 14

sweet curdling: alkaline ph and curd formation

Answer 14

Bacillus sp.
Proteus sp.
Micrococcus sp

Question 15

Gas production: explosion of curds

Answer 15

Clostridium sp.
coliform bacteria

Question 16

ropiness: stingy or slimy milk

Answer 16

Alcaligenes sp.
Klebsiella sp.
Enterobacter sp.

Question 17

Red rot: red colouration

Answer 17

Serratia marcescens

Question 18

Gray rot, gray colouration and foul smell

Answer 18

clostridium sp.

Question 19

C O N D E N S E D M I L K

Answer 19

Thermoduric bacteria - tolerates increased solutes
Presence of gas - Sucrose fermenting yeast

Question 20

E V A P O R A T E D M I L K

Answer 20

Swelling in cans - Clostridium spp
Coagulation - Bacillus cereus,
Bacillus subtilis