Dairy Science Midterm 2
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What is the purpose of centrifugal separation?
It separates the cream from the milk
How does centrifugal separation work?
In a centrifugal separator, bowl, the milk enters the disc stack through the distribution holes
What are the components to Stoke's law and what are the relationships to rate of separation?
- Particle diameter d m
- Particle density Pp Kg/m3
- Density of the continuous phase P1 Kg/m3
- Viscosity of the continuous phase n Kg/m,s
- Gravitational attraction of the earth g=9.81 m/s2
What is the purpose of homogenization?
Reduce creaming phenomena and modify texture/rheology of product
What are the typical operating pressures for homogenization?
- Operating Pressures – 500 – 3000 psi
- Operating Temperature – Sufficient for liquid fat
- Homogenization valve – narrow channel/orifice/gap
- Two stage (2000psi and 500 psi)
- Higher pressure – sufficient energy to break up
- fat globules to smaller particles
- Lower pressure – to break up loose
Why does homogenization slow the rate of rise (creaming)?
- reduce the size of fat globules to effectively reduce the rate of rise (separation/creaming) to be negligible for all practical purposes.
- Rate of rise is directly proportional to square of diameter
How are milk fat globules changed during homogenization?
- Absorption of whey proteins and caseins
- Reduction in density differences between fat globules and the aqueous phase of milk
What is the definition of pasteurization?
“ the process of heating every particle of milk and milk products to the minimum required temperature (for that specific milk or milk product), and holding it continuously for the minimum required time in equipment that is properly designed and operated”
What are the objectives of pasteurization of milk?
- Improve the keeping quality of milk
- render milk safe and nutritious by killing all Microbial pathogens that may be present in the milk and could be transmitted to people
What is difference between batch/vat pasteurization and HTST pasteurization?
- Batch/Vat: LTLT is 30 mins 145 F
- HTST: 15 seconds 161 F
What are the key components of an HTST pasteurizer and what is the function of each component?
- Balance Tank: provides continuous supply of milk to HTST, provides means to recirculate pasteurized milk
- Timing Device
- Heat Exchanger:
- Holding Tube: cannot be short circuited, proper upward slop (0.25 inch per running foot), temp cannot exceed 1 F and cannot be heated or insulated
- Indicating Thermometer: in indicate proper temp of product
- Recorder Controller & Sensor (STLR):records temps and times
- Recording Thermometer Charts
- Flow Diversion Device: acts as the only flow promoting device, must position pump to maintain lower pressures on raw milk compared to Pasteurized
- Vacuum Breaker: insures raw product doesn't siphon flow to pasteurized product in a power outage
What are the differences between pasteurized, ultra pasteurized, and ultra high temperature milk?
- Pasteurized: 72 C/ 161 F for 15 seconds, refrigerated, 10-21 days
- Ultra pasteurized: 138 C/ 280F for 2 seconds, refrigerated, 30-90 days
- Ultra high temperature: 138 C/280 F for 2 seconds + sterilized (has seal) shelf stable for 6+ months
What is the main cause of shorter shelf life in pasteurized milk products?
- Not sterilized
- it aims to reduce the number of pathogens that are likely to get you sick and cause disease
What is the "PMO" and what is it's use?
- Pasteurized Milk Ordinance
- a set of minimum standards and requirements that the FDA for regulating the production, processing and packaging of grade A milk
What are the names of three different names for fermented milk products and their country of origin.
- Yogurt -turkey
- Labneh -Lebanon
- Kumiss -Asia
- Kefir -Czech Republic
- Skyr -Iceland
- Lassi -India
- Doogh -Iran
- Ymer -Denmark
- Calpis -Japan
Why is "Metchnikoff" mentioned in the context of fermented milks?
He hypothesized that replacing or diminishing the number of putrefactive bacteria in the gut with lactic acid bacteria could normalize bowl health and prolong life.
What do clay pot shards have to do with ancient civilizations and the evolution of man as it relates to consuming milk products?
Evidence that the early farmers had used the pottery as sieves to separate fatty milk solids from liquid whey. That makes the Polish relics the oldest known evidence of cheese-making in the world
What is the difference between homofermentative and heterofermentative bacteria?
- Homofermentative:convert lactose to lactic acid
- Heterofermentative: convert lactose to lactic acid & citrate to acetaldehyde and pyruvate to diacetyl and carbon dioxide
What are the names (genus and species) of the two microorganisms that must be used in yogurt manufacture?
- Lactobacillus bulgaricus
- Streptococcus thermophilus
What are the requirements to use the National Yogurt Association Seal?
- It is voluntary identification available to all manufactures of refrigerated yogurt whose products contain at least 100 million (108) cultures per gram at the time of manufacture
- Meet the criteria for the activity test
- Cultures must be active at the end of the stated shelf life
What are the "typical" differences between greek yogurt and traditional yogurt (in terms of main proximate composition) and what two ways can be used to achieve these differences during greek yogurt manufacture?
Greek yogurt is thicker than regular yogurt with a higher protein content
What is the distinguishing processing difference in set vs stirred yogurt?
- Stirred yogurt is: ferment -> Break -> Stir/Cool -> Fill
- Set yogurt is: flavoring-> Fill Retail Container-> Ferment-> Cool/Store
Why is the extra high heat treatment necessary for the manufacture of high quality yogurt?
- High heat treatment causes denaturation of whey proteins. Specifically, denatured B-lactoglobulin reacts with K-casein.
- High heat treatment of milk stimulates the growth of Lb. bulgaricus, which in turn hydrolyzes milk proteins to provide free amino acids for the growth of S. thermopiles
What fermented dairy products are made with hetero-fermentative microorganisms?
- Sour Cream
- Creme Fraiche
What is the role of citric acid?
Used for: Buffering and mold inhibition
What is lactose intolerance?
- Are not able to fully digest the milk sugar (lactose) in dairy products
- Deficiency of lactase- an enzyme produced by the lining of your small intestine
What is lactase? What is beta-galactosidase?
- Lactase: an enzyme that catalyzes the hydrolysis of lactose to glucose and galactose
- Beta-galactosidase: a hydrolase enzyme that catalyzes the hydrolysis of B-Galactodidase into monosascharides
What are the symptoms of lactose intolerance?
Diarrhea, Nausea, and sometimes, vomiting, Abdominal cramps, Bloating, Gas
Why are people who are able to digest lactose as adults considered "mutants?"
Because years ago our bodies were not designed to digest milk after we had been weaned, but over the years humans have built up a tolerance and can know digest lactose as adults.
Why can some people who have mild lactose intolerance still consume yogurt?
It has lactase enzymes
What style/type of cheeses can people with lactose intolerance consume? Why?
Is lactose intolerance a type of milk allergy?
What defines a "milk allergy?"
- abnormal response by the body's immune system to milk and products containing milk.
- symptoms: wheezing, vomiting, hives and digestive problems
What component of milk is commonly associated with milk allergies?
- Casein which is found in the whey
- Whey which is found in the liquid part of milk that curdles
What defines a probiotic microorganism?
Live microorganism which when administered in adequate amounts confers health benefit on host
What is sweet acidophilus milk? Why is it called "sweet"?
- Non fermented milk
- Lactobacillus acidophilus makes it sweet
What are the top three cheese producing states in the US and what percent of the total cheese production do these three states produce?
- Over 50% of all US cheeses are made in these three states
Mozzarella, cheddar and other American cheese varieties makeup how much of all cheese produced in US?
73.2% of cheese produced in the United States
How was it realized that something in the lining of an animal's stomach could coagulate milk to make cheese?
- the enzyme chymosin is found in the stomach lining because it aids in digestion of mother's milk.
- chymosin from animals --(put into)--> yeast
What does FDB stand for, how is it calculated, and how is it associated with the cheese standard of identity?
- Fat on a Dry Basis
- (wt. fat)/(100-moisture)
What are the five main ingredients in basic cheese making and what are their functions in cheese manufacture?
- Milk: provides the fat and casein
- Culture: acidification (decrease pH, increase TA) Flavor and appearance, preservation
- Coagulant:Direct acidification, fermentation
- Salt: Moisture expulsion, preservation, flavor
- Color: Is associated with fat fraction
Which nutrients from milk are selectively concentrated in the curd and which nutrients are primarily removed in the cheese whey in most cheese making operations?
- Curd: casein, fat, moisture (aqueous) phase
- Whey: soluble proteins, minerals, lactose, organic acids, residual fat, starter enzymes
Roughly how many pounds of cheese are obtained from 100 lbs of milk in manufacture of Cheddar cheese from cow's milk?
Just under 12 pounds of cheese
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