Milk Quality

Question 1

Bacterial contaminants in milk including sources

Answer 1

From Interior of Cow: Mastitis organisms found to most often influence the total bulk milk count are Streptococcus spp. agalactiae, and Staphylococcus spp

From Exterior: Contribution of microorganisms from teats soiled with manure, mud, feeds, or bedding. In addition to Steptococcus and Staphylococcus you will also get Coliforms

Malty flavor tastes like Grapenut cereal. The cause is due to Streptococcus lactis in poorly cooled milk

Question 2

Yeast and mold contaminants in milk

Answer 2

Candida and Debaryomyces are the 2 most common Yeasts. Eurotium and Cladosporium are the two most common Molds

Question 3

Viruses/bacteriophage in milk

Answer 3

Bacteriophages attack Latic Acid producing bateria like Lactobacillis thereby effecting the proper ripening of a cheese. A specific phage population can increase rapidly if phage-sensitive cells are present in the starter culture. The consequent lysis of a large number of sensitive cells will delay or even halt the milk fermentation process leading to low-quality products.

Question 4

Major components in milk

Answer 4

Water: 80-87%
Fat
Protein (Casein): broken down through proteolysis into Amino Acids: Tyrosine, Tryptophan, Lycine and Taurine
Sugar (Lactose)
Vitamins (A, B1,2,3,6,12,D,E,K)
Minerals (Calcium and Phosphorus)

Question 5

Other milk quality parameters

Answer 5

Acid degree value: See Card
Sediment
Freezing point/added water
Bloody milk
Acidity of raw milk: normal acidity test results can vary from 0.13 to 0.17 percent lactic acid. Before a hint of acid taste can be detected, this will usually rise to above 0.20 percent
Human contamination: Malty flavor tastes like Grapenut cereal. The cause is due to Streptococcus lactis in poorly cooled milk

Question 6

Acid Degree Value

Answer 6

Rancidity is characterized by the release of free fatty acids because of the action of the lipase enzyme. When consumers taste rancid milk, they are detecting the short chain fatty acids. An Acid Degree Value test can be used to measure the presence of long chain fatty acids. There is about a 70 percent correlation between flavor and ADV.

Milk samples from individual farms should have ADVs of less than 0.80. When results exceed 1.00, the milk will have a soapy-bitter taste.

Question 7

Causes of Rancidity

Answer 7

Lack of adequate protein in the diet.
Not feeding enough total energy for the level of milk produced.
Milking cows longer than 305 days.
Added stress when milking cows more than two times per day.
Air leaks in pipeline milkers.
Flooding of pipelines and receiver jars.
Partial or less than every other day collection of milk from farms.
Freezing in the bulk tank.
Over agitation in the bulk tank.

Question 8

Major Pathogens in Raw Milk

Answer 8

Salmonella, Listeria, Staphylococcus aureus, E. coli, Campylobacter, Clostridia

Question 9

Milk Heat-Treatment Temperatures

Answer 9

Thermization: 131-158°F for 2-16 sec.
Bat/Vat Pasteurization: 145° for 30min
High Temp. Short Time (HTST): 161°F for 15sec
Higher Heat, Shorter Time (HHST): 191°F for 1sec
Ultrapasteurization: 280°F for 2 sec.
Ultrahigh Temperature (UHT): 240°F 4-15sec.

Question 10

SCC and SPC

Answer 10

Somatic Cell Count and Bacterial Standard Plate Count - 400,000 cfu/ml is the EU standard, 100,000 cfu/ml is the standard for Grade A milk. 750,000 cfu/ml is the standard created by the Pasteurized Milk Ordinance (PMO)