Milk Grading, Processing, & Hygiene Flashcards
What are the top 3 producers of milk in the world?
- India
- EU
- US
What are the 2 layers of cells in the mammary gland?
- LACTOCYTES (mammary epithelium) - milk-producing cells located on the surface inside the gland
- BASAL MYOEPITHELIUM - smooth muscle cells surrounding lactocytes
What surrounds each alveolus of mammary glands?
blood capillaries to provide nutrients for the synthesis and expression of milk
What hormone is necessary for milk secretion? Where is it secreted from?
oxytocin - causes myoepithelial cells to squeeze each alveolus to discharge the milk into the lumen of ductules
pituitary gland —> bloodstream
What are the 2 storage spaces for milk in the mammary gland?
- alveoli - 60-80%
- cistern - 20-40%
How many mammary glands do cows have?
4 quarters that are able to work independently from one another
What is the timeline for dairy cow mating and colostrum/milk production?
- heifers mate at 15 months
- give offspring by 2 y/o
- continues to give birth each year up to 9 y/o
- produces colostrum for 3-5 days
- produces milk for about 305 days (10 months) and is dry for 2 months
How does colostrum compare to milk?
- 2x more dry matter
- 3x more minerals
- 5x more proteins
- more fat-soluble vitamins
- viscous, thick, waxy, yellow
Why is colostrum not shipped to milk processing factories? Why must milk be properly processed?
not suitable for processing
milk has a nearly complete diet, but it is naturally in the pH and moisture danger zone —> conditions favored by bacteria
What are the 5 molecular components of milk? Why do dairy industries separate it into these components?
- water (87%)
- carbohydrates (4.9%)
- fat (3.7%)
- protein (3.3%)
- vitamins (1.4%)
allows for the production of diverse dairy products, like cheese, fat-rich butter, fat-free products, lactose-free products
How can adulteration of milk be observed molecularly?
proportion of milk composition will deviate from normal proportions
What are the 3 categories milk fats? Which ones produce essential fatty acids not made by the body?
- saturated fats (65%) - all single bonds
- mono-unsaturated fats (29%)
- poly-unsaturated fats (6%)
poly-unsaturated (omega) fatty acids —> linoleic, linolenic, and trans fatty acids
What 4 products are milk fats the raw material for?
- cream
- butter
- ghee
- fat-standardized liquid milk - fat-free, 1%, 2%, whole
What are the 2 categories of milk proteins? What are they based on?
- whey - soluble in water
- casein - insoluble in water
What is casein the major raw material for?
cheese
What are the 4 major vitamins and minerals found in milk?
- vitamin B12 - cobalamin, found only in food of animal origin
- vitamin B2 - riboflavin
- calcium - best dietary source
- phosphorus
What are the 3 major characteristics of milk used to distinguish contaminated from clean?
- aroma - no off-odors (ensure milk is not too hot)
- pH - 6.5-6.8
- titratable acidity - 0.13-0.17 (total concentration of free protons and undissociated acids in a solution that can react with a strong base and be neutralized)
What 7 major parameters are routinely checked by regulatory agencies for quality raw milk production?
- somatic cell counts - 750000 cells/mL
- bacterial counts - 100000 cfu/mL
- organoleptic quality - color, odor, taste, consistency
- chemical composition - water, fat, protein, mineral
- adulteration/residues
- pH - 6.5-6.8
- temperature - < 4 C
What 3 nutritional constituents are used to identify adulterated milk? What is the proper proportion of each?
- water (87%)
- fat (3.25%)
- non-fat solids (8.25%)
What are high somatic cell counts related to? Where in the process is this tested? What is the federal cutoff for Grade A milk?
mastitis —> udder health monitoring
storage of milk in bulk tanks
> 750000 cells/mL
What are bacteria counts related to? How is this tested? What is the federal cutoff for Grade A milk?
sanitary practices
standard plate count
> 100000 cfu/mL
What are the 4 methods of raw milk bacterial count? How are they done? What do each target?
- standard plate count/total aerobic colony count - serially diluted milk samples are plated on agar and incubated for 48 hr at 32 C —> general aerobic bacterial present in milk at pickup
- preliminary incubation count - hold milk at 12.8 C for 18 hours prior to plating —> subgroups of bacteria that grow well at refrigerator temps (psychrotrophic)
- lab pasteurization count - hold milk at 63.8 C for 30 minutes prior to plating —> subgroups of bacteria that survive heat treatment (thermoduric)
- coliform bacteria counts - plating on selective media that inhibits other bacteria (MacConkey) —> subgroups of bacteria that are associated with manure or environmental contamination
What is the most common cause of high bacteria counts? What are some other causes?
poor cleaning of milking systems allows milk residues to remain on the surface and provide nutrients for the growth and multiplication of bacteria that contaminate subsequent milking
- mastitis (Staph. aureus, Strep., coliforms)
- soiled cows
- unsanitary milking practices
- failure to cool milk rapidly to < 4 C
- failure of water heater
What 4 aspects of milk are observed to calculate organoleptic quality?
- COLOR - white
- ODOR - no off-odor
- TASTE - pleasantly sweet
- CONSISTENCY - liquid, but not watery
What are 3 causes of milk flavor changes? What part of this milk is responsible for taste change?
- environmental contamination - feed, barn, cow, weed, lacks freshness, stale
- bacterial/microbial - acidic, bitter, malty, fruity, fermented, putrid, rancid
- chemical/enzymatic/processing - ketotic, salty, rancid, bitter, oxidized, astringent, medicinal, flat
milk fat
What tends to cause acidic (sour), barn-like, bitter (beer), paper, and cooked flavor changes in milk?
- ACIDIC = sour lemon taste due to lactic acid produced by microbes due to poor refrigeration
- BARN = feces odor/taste due to poor ventilation, unclean condition, or ketosis
- BITTER = hops taste due to break down of milk proteins by microbial enzymes
- PAPER = milk absorbed odor of carton pack
- COOKED = boiled by improper pasteurization
What tends to cause cow-like, feed-like, flat, garlic/onion, rancid, and salty flavor changes in milk?
- COW = cow breath or fecal odor due to acetone during ketosis or acetonemia
- FEED = silage, hay, grassy flavor due to feeding before milking
- FLAT = watery, adulteration by water addition
- G/O = consumption of garlic weed
- RANCID = soapy, putrified fat due to the release of FFA by microbial destruction of milk fat
- SALTY = late lactation, mastitis
When are pH, temperature, and drug residues measured in milk? How?
rapid on-site milk test —> avoids contamination before shipment
- pH = measure to be 6.5-6.8
- temperature = measured to be < 4 C
- residues = tests negative by lateral flow assay
What are 3 advantages to milk grading?
- standardized milk prices
- determines type of milk sold on liquid form
- determines the types of milk that require further processing (for cheese) before consumption
What 4 criteria used to grade milk?
- chemical constituents
- load of bacteria
- bulk tank SCC
- organoleptic features
What are the 3 milk grades?
- certified - < 10000 cfu/mL bacteria
- grade A - < 100000 cfu/mL bacteria
- grade B - < 500000 cfu/mL bacteria
What is grade B milk used for?
not sold as liquid milk due to poor quality —> processed for other products, like cheese, before consumption
Milk grading criteria:
How is milk processed?
milk composition is manipulated to form another dairy product by pasteurization and cooling followed by separation, standardization, or fermentation
What is the point of pasteurization? Cooling?
PASTEURIZATION - > 63 C kills microbes
COOLING - < 4 C (except cheese and yogurt) prevents the growth of microorganisms using cold water, ice water, brine solution, or alcohol solution (glycol)
What are the 4 types of milk pasteurization?
- ultra-high temperature - 120-140 C for 2-4 sec (long shelf life)
- canned - 115-120 C for 15-20 mins using autoclave or treatment chamber
- high temperature, short time (flash) - 72-74 C for 20 secs (widely used)
- low temperature, long time (batch) - 63 C for 30 mins
(higher temperatures are even able to kill vegetative bacteria, like Coxiella burnetii)
How are yogurt and cheese pasteurized?
YOGURT - 40-45 C for 15 mins, then cool to needed temp for fermentation
CHEESE - 30-35 C for 15 mins, then cool to need temp for fermentation
What is the most common cooling step in the dairy industry?
keep dairy products at < 4 C at all steps of the process by refrigeration cold-holding
What is thermization?
type of pasteurization at 57-68 C for 15 mins that targets pathogenic bacteria and leaves good bacteria in the product —> low temp will not alter structure and taste of milk
How are milk components sorted?
nono-pore membrane technology —> micro, ultra, nanopore membranes
What are the 5 general steps for milk processing?
- COLLECTION - collected from dairies and stored in tanks that cool it to < 4 C and transferred to plant
- SEPARATION - sedimentation, debris, and bacteria removed from milk (heavier and lighter milk are also separated to form cream and skim milk)
- PASTEURIZATION - milk is heated and cooled
- STANDARDIZE - fat homogenizing through atomizer to stop fat from floating to the top
- PACKAGING - packed in cartons for retail or further manufactured for other material
Cheese production:
What 4 products of milk are based on water/moisture content?
- whole milk - 87% water, 13% solid
- evaporated canned milk - 60% of water removed
- sweetened condensed milk - 60% of water removed and replaced by sugar
- dry/powdered milk - water entirely removed
What is whey?
liquid part of milk without any solids
What is yogurt? Cheese?
YOGURT = cultured milk with starter Lactobacillus bacteria
CHEESE = cultured milk with starter Lactobacillus bacteria and rennet enzyme, solid part is removed from liquid part
What 3 milk products are based on fat content?
- ghee - butter clarified to remove its milk solids and water content, leaving 99-100% pure fat
- butter - fat and protein components of churned cream
- cream - higher fat layer skimmed from the top of milk before homogenization
What cattle breeds produce premium milk? Why
Golden Guernsey or All-Jersey
higher milk fat content and creamier taste
What are the top 5 biological hazards associated with milk and its products?
- Listeria monocytogenes
- E. coli
- Salmonella
- molds and yeast
- Staph
