1. Milk and Dairy (Part I) Flashcards
what is the major component of cow milk?
what are other components?
moisture (87.5%)
others: sugar, fat, protein, minerals
what monosaccharides is lactose broken down into?
glucose and galactose
describe milk transportation into the lumen
- oxytocin binds to secretory cells (SC)
- milk fluid is expelled into lumen
- milk flows from lumen to cistern
- fat globules are synthesized by ER and added to milk fluid in lumen
- milk proteins (casein, beta lactalbumin, beta lactoglobulin) are synthesized by ribosome of SC into milk fluid
what are the two forms of lactose?
how are they different nutritionally?
how are they different in terms of solubility?
how are they different in terms of sweetness?
alpha and beta
they are nutritionally the same
solubility:
- alpha is more soluble at lower temp
- beta is more soluble at higher temp
sweetness:
- beta is sweeter than alpha
what is the result of alpha and beta lactose having different solubility at different temperatures?
the ratio of alpha to beta lactose depends on the temperature of the solution/milk
since beta is sweeter than alpha, temperature will affect the sweetness perceived of lactose
what is BST?
- bovine somatropin hormone
- to aid milk production in cattle
- when BST is added from external sources, this boosts milk production
what are two major types of milk proteins?
casein and whey
the high fat content in milk causes it to be very prone to….
oxidation and spoilage
milk fat has a higher proportion of ____ fats and lower proportion of ____ fats
saturated
monounsaturated
with humans, cow and reindeer milk, which has the most and least PROTEIN?
humans: least
cow: most
reindeeer: intermediate
with humans, cow and reindeer milk, which has the most and least SUGAR?
humans: most
cow: intermediate
reindeer: least
with humans, cow and reindeer milk, which has the most and least fat?
humans: most
cow: intermediate
reindeer: least
why is it better to breast feed babies?
- human milk has antibodies
- human milk is higher in sugar (good energy sourcE)
what kind of lipid molecule is most abundant in milk?
TAGs (triacylglycerols) - 95%
the amount of DAGs and MAGs is very small
how many free fatty acids in milk engage in the esterification of glycerol?
what is the significance of this?
around 400. But only around 30 of them constitute around 90% of the FFA found.
thus, many are found in only very small concentrations
describe the structure of phospholipids
contains one highly polar phosphate group where the 3rd FFA would be
what enzyme is tightly bound to the membrane and associated with phospholipids?
what happens when the membrane is disrupted?
what is a solution to this?
lipoprotein lipase
when the enzyme is bound to the membrane, it does not act on the lipids in the membrane
however, when the membrane is disrupted, the enzymes come in contact with the lipid and breaks it down, causing spoilage and deterioration.
thus, lipoprotein lipase must be inactivated by pasteurization prior to homogenization of milk
why can raw milk be kept for several days without development of rancid flavors?
because milk fat globules have double layers of lipoprotein
spoilage will not occur if globules remain intact
what is happening when milk is separating?
fat and serum forms two distinct layers
is the separation of milk desirable or not?
depends. It is not desirable in liquid milk, but it is sometimes desirable in other dairy products (eg. cream)
what is a solution to milk separation?
homogenization
what is homogenization?
breaking up fat into small globules that will emulsify into the milk solution
which type of fat has the highest abundance in milk?
A) saturated
B) monounsat
C) polyunsat
saturated fats (60% of all fats)
polyunsat are the least (5% of all fats)
what are the most common monounsat fats in milk?
C16:1 (palmitic) and C18:1 (oleic)
which saturated fats are synthesized from mammary glands?
which sat fats are derived from the diet of the animal?
mammary glands: C4-C14
derived from diet of animal: C16 and C18
what are the most common polyunsat fats in milk?
C18:2 (linoleic) and C18:3 (linolenic)
why does milk have a broad melting temperature?
since milk fats are not uniform, which results in a large range of types of milk fats
what is the range of melting temperature of milk?
-40 to 40deg C
what is the significance of the large range of melting temp of milk?
enables ease of spreadibility of fat (eg. butter)
what are the 2 approaches to separation of milk
- gravitation separation
2. centrifugal separation
describe what occurs with acidification of skim milk with acetic acid
- acetic acid causes casein molecules to precipitate, while whey proteins stay in solution in presence of Ca2+
- once casein has precipitated, it is removed by filtration of centrifugation
which casein is not precipitated at acidic pH?
kappa casein
what are unique functional and structural properties of kappa casein?
functional
- it does not precipitate at acidic pH
- it is smaller than other caseins
- has a low degree of phosphorylation
- does not bind to Ca (remains soluble in milk in presence of Ca2+ ions)
- occurs as a trimer (from disulfide bond formation between cysteine residues)
- is has a CHO moiety attached to it
describe the steps of gravitational separation
- put milk in shallow tanks
- cream will separate
- cream is skimmed off the top
- liquid is drained from the bottom of the tank
which one is more efficient? why?
A) gravitational separation
B) centrifugal separation
centrifugal
because gravitational will lose around 5% of the cream
describe centrifugal separation
spinning milk solution in a centrifuge to separate cream from liquid
what are unique properties of casein?
- high in phosphate groups
- can bind Ca extensively
- most caseins precipitates at acidic pH (4.3-4.5). Except for kappa-caseine
- high AA content
in caseine, where is phosphorus mostly found?
as a complex with the AA serine (phosphoserine) and threonine (phosphothreonine)
why is milk a good source of calcium?
because casein binds with calcium extensively
what are the most prominant types of caseins?
alpha s1 casein alpha s2 casein beta casein kappa casein gamma casein
lambda casein is a breakdown product of ____
alpha s1 casein
gamma casein is a breakdown product of _____
beta casein
what AAs are caseins particularly high in?
essential AAs
which caseins lack cysteine?
alpha and beta forms (the major caseins)
why do caseins have strong aggregation capacity?
due to the hydrophobic and non-polar AAs
describe the polarity of casein
- overall non-polar
- but some regions have high polarity from P groups as well as glutamate and aspartate residues
what are the 3 types of whey proteins?
- lactalbumin
- immunoglobulins
- serum albumin
how does lactalbumin promote lactose synthesis?
by activating enzyme galactosyl transferase
where is immunoglobulin and serum albumin synthesized and then transported?
synthesized in the liver, then transported to mammary glands
what is the main function of serum albumin?
to transport fat molecules
do whey proteins have phosphate groups?
no
do whey proteins have calcium binding?
no
what is the predominant whey protein?
beta lactoglobulin
what is the function of beta-lactoglobulins?
the exact function is not clear
where are beta lactoglobulins manufactured?
in mammary glands, and then added to milk fluid
what is the 2nd most abundant whey protein?
alpha-lactalbumin
where are alpha-lactalbumins manufactured?
in mammary glands, and then added to milk fluid
what is the function of alpha-lactalbumins?
modifies activity of the enzyme galactosyl transferase, which transfers galactose units from UDP-galactose to protein
what is BSA?
bovine serum albumin
where is BSA produced?
in the liver. It enters milk through the bloodstream
what is the function of BSA?
FFA carrier
where are immunoglobulins produced?
in liver and enters milk through blood stream
what are the 3 classes of immunoglobulins in cow’s milk?
IgG
IgG2
IgA
IgM
what is the composition of immunoglobulins?
2 light chains and 2 heavy chains
what is the function of immunoglobulins?
to provide passive immunity to calves until they are old enough to synthesize their own
what are proteose-peptones?
proteins that remain in solution after milk has been heated and acidified
what is the disadvantage of removing all fat in skim milk?
this removes many fat soluble vitamins too
mostly vit A and vit D
what are the main minerals in milk?
calcium phospate sodium potassium chloride
what are the two isomer forms of lactose?
alpha and beta
how are alpha and beta lactose the same or different?
they are nutritionally the same, but isomerically different and have different solubility
describe how the stability of alpha and beta lactose is effected by temperatures
at lower temp (below 93C), alpha is more soluble
at higher temp (above 93C), beta is more soluble
thus, there are different ratios of alpha and beta at different temperatures. Since beta lactose is sweeter than alpha, the temperature will affect the sweetness perceived of lactose
which is sweeter?
A) alpha lactose
B) beta lactose
beta
what forms can the glucose molecule in the lactose exist as?
alpha pyranose form
beta pyranose form
what form can the galactose molecule exist as?
only the beta pyranose form
which is more stable?
A) alpha lactose
B) beta lactose
alpha
alpha and beta lactose refer to the ____ form of the glucopyranose ring
anomeric
rank the sweetness level
A) lactose
B) sucrose
C) galactose and glucose
sucrose
galactose and glucose
lactose
what enzyme hydrolyzes lactose?
what are the breakdown products of lactosE?
beta-galactosidase
breaks down into galactose and glucose
how is lactose free milk produced?
by treating milk with beta 1,4 galactosidase
how many hours does it take for milk to separate after being produced from a cow?
48 hrs
what tests need to be carried out on milk after its production?
- microbial tests
- moisture content: useful to prevent fraud since milk can be easily diluted to a bigger volume
- total solids: measuring lactose
what are uses of lactose in pharmaceutical industries?
as a filler or as a coating material for tablets (due to film forming properties)
why is raw milk more perishable and risky?
- lack of processing means enzymes/microorganisms which cause spoilage are still present
- some microorganisms are pathogens
in canada, is it permitted to give out raw unprocessed milk outside a farm?
no, due to the food and drug act
describe the storage and transport of milk on the farm
- milk is collected and immediately cooked and held at <4.4C in refridgerated holding tanks
- milk is delivered from farm to processing plant of to central receiving station where it is blended with other milk
what factors does quality control involve?
moisture content density total solids sediment microbial analysis flavour
what are tests used during milk processing for quality control?
- determination of fats and total solid content
- estimation of amount of sediment
- microbiological tests (total bacterial plate counte, coliform count, etc…)
- determination of freezing point
- assessment of milk flavour
off flavours of milk can result from..
- absorption of odours
- degradation of fat by lipase (due to lipase enzyme)
- oxidation of fat (promoted by contact of milk with copper or iron equipment)
describe how milk is clarified
removing impurities by feeding milk through a clarifier
or using a centrifugal milk clarifier
what are 2 main types of milk treatments?
heat treatment
homogenization
how do you determine the type of heat treatment to use?
depends on final use of milk
what are the 4 types of heat treatments used for milk?
describe each one.
- pasteurization: batch or high temp short time (HTST). 72degC for 15s
- thermization:
- 65C for 15-20s
- doesn’t denature enzymes of microorganisms
- product texture outcome is desired for certain cheeses (eg. cheddar) - ultra high temp (UHT)
- indirect heating of milk by coils/plates (136C for 5-8s)
- or direct heat by steam injections (140C for 2-4s)
- followed by rapid cooling and aseptic packaging - sterilization
- heating in autoclave
- 110C for 20-40 min
- or 120-130C for 8-12min
- ills all enzymes and microorganisms
which heat treatment kills all enzymes and microorganisms?
sterilization
which heat treatment does no denature enzymes or microorganisms?
thermization
what is homogenization?
- forcing milk through a small opening under high pressure
- this causes the milk fat globules to break down into smaller particles to stay suspended in aqueous solution
why is homogenization necessary?
since milk is an emulsion and subject to phase separation
what is creaming?
when raw milk is left to stand for over 30 mins, fat separates as a cream layer on top, apart from the aqueous phase
based on density differences
what can creaming be used for?
to remove fat from milk for production of reduced fat products
what are 2 approaches to creaming?
gravitational and centrifugal
what does speed of separation or creaming velocity depend on?
- size of fat particles
- density ratio between fat and aqueous medium
- speed of rotation (for centrifugal creaming)
what is creaming velocity proportional to?
- particle size
- density difference between aqueous and fat phase
- speed of rotation
- treatment time
what is the equation for specific viscosity?
x = specific viscosity = viscosity of fat phase / viscosity of aqueous phase
what is the equation of creaming velocity in centrifugation?
V = r^2 * (d1-d2) * r1 * w^2
where:
r1 = radius of rotor
w = angular velocity
