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Which hormone stimulates milk production?
How is milk produced in the body?
- Oxytocin binds to secretory cells
- Milk fluid expelled into lumen
- Milk flow from lumen into cistern
- Ft globules synthesized by ER and added to milk fluid in lumen
- Milk proteins are synthesized by ribosome of secretory cells into milk fluid
- Other components are synthesized elsewhere and transported in bloodstream to add to milk fluid
- Electrolytes are transported via pumps or channels through lateral membranes connecting epithelial cells into the lumen
How are electrolytes added to milk?
Electrolytes are transported via pumps or channels through lateral membranes connecting epithelial cells into the lumen
How are milk proteins added to milk during production?
Synthesized by ribosome of secretory cells into milk fluid
How are fat globules added to milk?
Fat globules synthesized by ER and added to milk fluid in lumen
What is the lactation period of cows?
What is the average milk production per cow?
What is bovine somatotropin?
Used to boost milk production in some countries
Why is the use of bST not permitted in Canada and some European countries?
the use of rBST substantially increased health problems with cows, including foot problems, mastitis and injection site reactions, impinged on the welfare of the animals and caused reproductive disorders. The report concluded that, on the basis of the health and welfare of the animals, rBST should not be used.
How much fat is in milk?
The amount of fat in milk is about 4.6%
What is the most abundant type of fat in milk?
What functions as an emulsifier in milk?
Diacylglycerols function as emulsifiers to bring the aqueous phases together as a stable emulsion
What is the best known phospholipid in milk?
What is lecithin?
- The best known phospholipid in milk
- An emulsifier, biological function of lipid bilayers in biological membrane
What is the most abundant type of fatty acid in milk?
Saturated fats are the most abundant
What do MUFAs do?
The MUFAs bind or remove undesirable fats like LDL and chylomicrons
How do MUFAs effect the concentration of HDL?
- The MUFAs bind or remove undesirable fats like LDL and chylomicrons
- Thus, the proportion of HDL cholesterol is made relatively higher by the MUFAs
NEED TO KNOW DIFFERENCE BETWEEN OMEGA 3 AND OMEGA 6
- Linoleic acid (LA; omega–6; 6; 18:26) is the parent fatty acid of theomega–6 group. Linoleic acid must be supplied to the body by the diet, becausethe body is unable to synthesize it. All other members of the omega–6 group are derivatives of LA.
- Similarly, the parent compound of the omega–3 group is alpha-linolenic acid (ALA, omega–3, 3, 18:33). All other members of theomega–3 group are merely derivatives of ALA, and together they form thepolyunsaturated fatty acids (PUFA).
- In each group, the derivatives can convert tolonger chain fatty acids by using two mechanisms; desaturation and elongation. The enzymes that are involved in these mechanisms have the same functions in the two fatty acid groups, and therefore the omega–6 and omega–3 fatty acids ‘compete’ for the same enzymes.While from a chemical point of view the differences between omega–6 andomega–3 acids are very small, and may appear insignificant, they exert different and sometimes even opposite effects. These opposing effects are not easilyexplained. It was recently suggested that the distinction between omega–6and omega–3 PUFA is based on the differential capacity of protein in large, and membrane-bound protein in particular, to ‘recognize’ various PUFA.
How do PUFAs cause undesirable flavors in milk?
PUFAs in milk are highly prone to oxidation because of their high degree of unsaturation- leading to oxidized flavors in milk (not desirable)
What enzyme is responsible for the oxidation of PUFAs in milk?
Why does homogenized milk need to be pasteurized?
- There are phospholipid bilayers that enclose fat globules
- When the membrane is in tact, the lipoprotein lipase does not have access to the PUFAs and oxidation does not occur
- Once the membrane is disrupted (as occurs during homogenization) the enzyme is released to gain access to the PUFAs and oxidize it to produce rancidity
- Pasteurization inactivates lipoprotein lipase and prevents oxidation
What is the difference between conjugated linoleic acid and linoleic acid?
- CLA has been shown to produce fat loss and muscle mass gain in experimented animals
- Some individuals promote use of this compound for weight management
How does phase separation in milk occur?
- Fat globules coalesce to form large globules
- Large globules rise to the top of milk, this leads to phase separation
How is phase separation in milk controlled?
Why do milk fat globules coalesce?
The phospholipid bilayers are polar in nature, as such, they attract and coalesce to form larger globules that float to the top of the aqueous phase because of their lighter density
Why is milk phase separation desirable?
Production of butter and other diary products such as cream
Which caseins are larger?
Alpha and Beta are the larger caseins (180-200 amino acids)
Which amino acids is casein high in?
Hydrophobic amino acids (tryptophan, phenyl alanine, leucine, isoleucine)
Which mineral is casein high in?
What happens to the Ca2+ in milk?
The Ca2+ binds to the other caseins (apart from kappa casein) and cause the casein molecules to precipitate as Ca-Caseinate at the appropriate pH
What causes caseins (other than kappa casein) to precipitate?
The Ca2+ in milk binds to the other caseins in milk (apart from kappa casein) and case the casein molecules to precipitate as Ca-Caseinate at the appropriate pH
Why is calcium-caseinate important?
Calcium caseinate is used as a common basis for separating proteins
How is calcium-caseinate precipitated?
Acids like acetic acid or propionic acid may be used to adjust pH to 4-5 to cause precipitation
What are whey proteins?
Proteins in solution after caseins are removed from the milk
What is beta-lactoglobulin?
The major whey protein
What is beta-lactoglobulin high in?
High in essential amino acids and thus a good nutrient source
What does beta-lactoglobulin do in the body?
Binds hydrophobic compounds such as fats, some proteins and amino acids and transports them across the biomembranes and in body fluids
What does alpha-lactalbumin do in the body?
Regulates the activity of the enzymes that synthesize the milk sugar (lactose), Lactose synthase and beta-galactosyltransferase
Where is alpha-lactalbumin found?
In the whey protein of milk
What is the purpose of immunoglobulins in milk?
Impart passive immunity to infants from their mothers until they can make their own immunoglobulins or antibodies
What is serum albumin?
- Larger molecular weight globular protein comprised of ~600 amino acids
- High in essential amino acids and is a good nutrient source
- Also binds lipids to protect them from oxidative demise
Milk caseins are classified into various types, what are the distinguishing features of these molecules
- alpha(s1)-casein: (molecular weight 23,000; 199 residues, 17 proline residues)Two hydrophobic regions, containing all the proline residues, separated by a polar region, which contains all but one of eight phosphate groups. It can be precipitated at very low levels of calcium.
- alpha(s2)-casein: (molecular weight 25,000; 207 residues, 10 prolines)Concentrated negative charges near N-terminus and positive charges near C-terminus. It can also be precipitated at very low levels of calcium.
- ß -casein: (molecular weight 24,000; 209 residues, 35 prolines)Highly charged N-terminal region and a hydrophobic C-terminal region. Very amphiphilic protein acts like a detergent molecule. Self association is temperature dependant; will form a large polymer at 20° C but not at 4° C. Less sensitive to calcium precipitation.
- kappa-casein: (molecular weight 19,000; 169 residues, 20 prolines)Very resistant to calcium precipitation, stabilizing other caseins. Rennet cleavage at the Phe105-Met106 bond eliminates the stabilizing ability, leaving a hydrophobic portion, para-kappa-casein, and a hydrophilic portion called kappa-casein glycomacropeptide (GMP), or more accurately, caseinomacropeptide (CMP).
- Isoelectric precipitation is achieved by lowering the pH of the solution to the isoelectric point
- The isoelectric point is the point at which the charge of the protein is neutral
- When the protein is neutral, it will not be attracted to anything in the solution and form aggregates with itself, hence precipitating
What amino acid do all major caseins lack?
Explain the role of kappa-casein in micelle formation
- κ-casein molecules that stabilize the micellar structure. There are several models that account for the special conformation of casein in the micelles
- All 3 models consider micelles as colloidal particles formed by casein aggregates wrapped up in soluble κ-casein molecules. Milk-clotting proteases act on the soluble portion, κ-casein, thus originating an unstable micellar state that results in clot formation
How is kappa-casein different than the other caseins?
Kappa-casein remains soluble in milk in the presence of Ca2+ ions
What happens to kappa-casein under reducing conditions?
Under reducing conditions, kappa-casein shows 2 cysteine residues
How are casein micelles held together?
Calcium ions and hydrophobic interactions
What are casein micelles?
Suspended particles, not completely soluble
What causes casein to combine with phosphate?
Serine and threonine residues
What happens when there is a loss or removal of acid in milk?
Isoelectric precipitation cannot occur, so we get predominantly the molecule in the monomeric form
How is calcium removed from milk?
A calcium chelating agent
What are the two parts of kappa casein?
Has a protein part and a carbohydrate part (the tail)
What are casein monomers?
How does kappa casein interact with casein monomers?
Kappa casein can bind to the monomer
What is the significance of the tail on kappa casein?
So long as the tails are intact, it protects the molecule from aggregating to form a large micelle
What happens in milk when the pH is decreased, the temperature is increased, or chelating agents are added?
Hydrophobic interactions become very easy so it will become easy to remove the tail from kappa casein, and it can now bind to calcium and form calcium caseinate
What happens when the tail is cleaved off of kappa casein?
It is called para-kappa-casein, which binds to calcium and forms calcium caseinate which can precipitate
Which proteins are capable of breaking kappa-casein into para-kappa-casein?
In theory, every proteolytic enzyme should be able to bring about this reaction
Which enzyme is often used to cleave kappa casein?
Chymosin (rennet) is often used to cleave kappa-casein between phenylalanine 105 and methionine 106 of kappa casein
What is formed when rennet breaks down kappa casein?
Para-kappa-casein and a glycomacropeptide
What happens if pepsin is used for cheesemaking instead of rennet?
Pepsin also breaks dow other peptide bonds, so the yield of cheese is much lower because the molecules become smaller, so in the process of straining you lose some cheese
What happens if there is uncontrolled proteolysis during cheese making?
They can keep on breaking peptide bonds to form smaller peptides that can effect the taste of the cheese, due to the formation of beta-peptides
Where is rennet found?
In calf stomach- no produce microbially in labs
What needs to be present in order for para-kappa-casein to precipitate?
How is the cleavage rate of kappa casein increased?
Replacement of Met-106 by phenylalanine (genetic manipulation) increases hte bond cleavage rate by ~80%
What is the difference (structurally) of alpha and beta lactose?
If the -OH group is in the same direction of the CH2OH group, it is beta
How is alpha and beta lactose separated?
If you take a supersaturated solution of lactose, the alpha form will crystallize below 93.5°C, whereas the beta for, will crystallize above 93.5°C
Is there commonly more alpha or beta lactose?
THe proportions of alpha and beta tends to have more than alpha, but the proportions of alpha to beta forms decrease with temperature
Which form of lactose is more soluble?
The beta form tends to be more soluble than the alpha form
Why are acids important in milk?
Acids give milk flavour and preserve the milk by controlling microbial growth and deactivate enzymes
Why is milk still prone to spoilage, eventhough it is acidic?
In milk, there are mot enough acids to control all the microbial and enzymatic activity, so it is still prone to spoilage
Which minerals are present in milk?
K+, Ca2+, Na+, Mg2+
What vitamins are present in milk?
C, B5, B2, B3, E
Which vitamin is milk very low in?
Which group of vitamins is milk generally high in?
Why is the density of milk products important?
- Used to convert volume into mass
- Used to estimate the solids content
What does the density of milk depend on?
- Composition of the material (especially fat content)
How are enzymes in milk inactivated?
Which enzyme breaks down hydrogen peroxide?
What is hydrogen peroxide broken down into?
Water and oxygen
Why dont we want hydrogen peroxide in milk?
Very reactive, can cause oxidative damage, can be a source of free radicals (BAD)
What is cold pasteurization?
Hydrogen peroxide is added to milk to sterilize
How is lactoperoxidase a natural bacteriodice?
Lactoperoxidase is able to oxidize halides to hypohalites and thyocyanates to hydrothiocyanite- these products are able to kill bacteria
How is sulfhydryl oxidase used to stabilize protein?
Sulfhydryl oxidase can oxidize thiol (-SH) groups in proteins, peptides and amino acids to form disulfide bonds that can help stabilize protein and related molecuels
What does superoxide dismutase do?
- Converts O2+2H+--> H2O2
- Which can then form water and oxygen
What does xanthine oxidase do?
- ATP-->ADP-->AMP-->IMP-->hypoxanthine-->xanthine-->uric acid
- Conversions of hypoxanthine to xanthine and xanthine to uric acid are catalyzed by xanthin oxidase
What are water and xanthine converted to?
Uric acid and hydrogen peroxide
What is plasmin?
- A proteolytic enzyme
- Breaks down plasma proteins that may become part of milk
What is prolactin?
A hormone that simulates the mammary glands to produce milk
What hormone stimulates the mammary glands to produce milk?
What is the purpose of insulin?
- Regulates the uptake and storage of glucose- stored in liver as glycogen
- Inhibits lipases that break down lipids, thus leading to increased levels of fats (as triglycerides)
What is the purpose of thyroxine?
Hormone responsible for regulating rates of metabolism
What is IGF carrier protein?
Responsible for transport of IGF
What is IGF?
Insulin-like growth factor- resembles insulin in both structure and function
Why is the consumption of raw milk considered risky?
Because raw milk can contain harmful pathogens such as mucobacterium bovis, salmonella, E. coli 0157:H3
Once milk is collected, what is done to it?
It is immediately cooled and held at <4.4°C in refrigerated holding tanks
What is the price of milk based on?
Why is microbial analysis done on milk?
To establish total microbial organisms and types of microorganisms presnet in the milk
Why is the moisture content of milk important?
Need to establish the freezing point
How is milk clarified?
What is heat treatment of milk used for?
Used to kill microorganisms and deactivate enzymes
What is HTST processing?
Heat milk to 72-74°C and hold it for about 15-20 seconds
What is thermization of milk?
- Level of heat applied is slightly lower than HTST (60-65°C) for about 15-20 seconds
- In this mode, enzyme sare not completely deactivated as they are required during further processing of this product into tother products (such as cheese)
What is UHT processing?
- Much higher temperature is used for a much shorter time
- 135-238°C for 5-8 seconds
- Use indirect heat
- Direct injection of steam into the milk at a higher temperature for a much shorter time (140-145°C fo 2-4sec)
- Followed by rapid cooling and aseptic packaging
How is milk sterilized?
- Heating in autoclaves
- 110°C for 20-40 mins
- 130-140°C for 8-12 mins
Why is milk homogenized?
Done to stabilize milk emulsions
How is milk homogenization done?
- Either by ultra-sonication of high pressure agitation
- Or glycopeptide is attached to kappa casein which is hydrophilic so it remains in solution
Why is the determination of the freezing point of milk important?
To check for pick-up of H2O
Why is stainless steel equipment used for milk processing?
Copper or ion in milk-handlin equipment can promote oxidation of fat
Why is milk clarified?
To remove impurities such as sediment, animal cells, and some bacteria
How is milk clarified?
- By feeding it through a clarifier (self-cleaning disk separator) via a de-aerating vessel
- These separators can process wither cold or warm milk
What is high pressure homogenization?
- The milk is forced through a homogenization valve or small orifice, and the fat globules are reduced in size to a diameter of less than 1um by turbulence, cavitation, and shear forces
- Up to 35MPs, 50-70°C
What is creaming?
Used to remove fat from milk for various purposes, including the production of reduced-fat milks as well as various dairy products
Why do fat globules rise to the top of the milk?
Because fat globules are lighter
What is milk plasma?
Everything that is not cream
How does gravity separation work?
Just leave it to stand and wait for the cream to rise to the top
What are the 2 different forms of gravity separation of milk?
Shallow pan metod, Deep setting method
What is the shallow pan method of gravity separation?
Milk is placed in shallow pans and left to stand for some time, the cream rises to the top and is ladled off
What is the deep setting method of gravity separation?
Narrower containers of higher depth are used. The cream floats to the top and the aqueous plasma is drained off from the bottom
Other than gravity separation, what is the other method of milk separation?
According to stokes law, what does the velocity of a particle depend on?
The size or radius of the particle
What factors influence the velocity of separation of cream from aqueous phase?
Size and temperature
How does temperature effect the velocity of particles during separation?
- Temperature effects the velocity because it causes the size of the fat globule to get bigger. Temperature also effects density of both phases and the specific viscosity
- Density difference will decrease with an increase in temperature
What is the problem with gravity separation?
- It isnt efficient-about 0.5% of the fat is retained with the aqueous phase
- Time consuming
Why is centrifugal separation more efficient than gravity separation?
- <0.1% of fat left with aqueous phase
- Process is much faster
How does fortification change the density of milk?
Once you fortify a milk product with vitamins and minerals, it will change the density and make it more dense
Approximately how big is the shallow pan method of separation?
What principle is centrifugal separation based on?
Based on the fact that when liquids of different specific gravities revolve around the same centre at the same distance (r) with the same angular velocity (ω), a greater centrifugal force is exerted on the heavier liquid than on the lighter one
What are some advantages of powdered versus regular milk?
- Powdering reduces bulk
- Removal of water renders the product more stable and less susceptible to microbial activities
- Ease of transportation and distribution
- facilitates incorporation into various food products such as infant food formula
What is powdered milk often used for?
Used for reconstitution of milk in certain countries that have no dairy farming for various reasons, or as intermediate products for further processing into infant formula, milk chocolate, etc
Which drying process is often used to make powdered milk?
- Drying process mostly used is spray drying, although drum drying (with or without vacuum), and fluid-bed drying (foaming with inert gas N2 or O2 are used for special purposes
What is the drying temperature for milk?
Drying temperature normally does not exceed 70°C
What is significant about the temperature for drying staying below 70°C?
The whey proteins do not denature and many enzymes are still active (and can cause oxidation of fat during storage or enzymatic browning)
How does spray drying work?
Milk and hot air are fed into the drying chamber, and then passed through a cyclone to separate the air from the dried product
How does drum drying work?
Milk is applied as a thin film to the surface of a heated drum, and the dried milk solids are then scraped off with a knife
How does fluid-bed drying work?
A gas (usually air) is passed through milk layered on a bed under controlled velocity conditions. Air and water vapor are separated from the dried powder which is collected via an outlet
What is reconstituted milk?
Adding powdered milk to water (1:10 ratio) which is good for regions where milk product is minimal or non-existant
What is filled milk?
In this, other fats (vegetable oil or non-cow derived milks) are added to the regular cow milk
What is toner milk?
H2O and milk powder are added to regular cow milk
What is lactose-free milk?
In this, beta-galactosidase is used to break down lactose in milk
How is low-sodium milk made?
Use microfiltration to remove sodium
Are proteins higher in skim milk or whole milk?
Since proteins are water soluble, they tend to be higher in skim milk than in whole milk or buttermilk
Which tends to be more nutrient dense, skim milk or whole milk?
Is dehydrated milk more nutrient dense than regular milk?
Yes, dehydrated milk is depleted in water but enriched in other components such as protein, fat, carbs, and minerals
What is done with cream after it is separated from the milk?
- Direct consumption
- Production of butter and ice cream
How much fat is whipping cream?
At least 30%
How much fat is in coffee cream?
At least 10%
How much fat is in buttercream?
How can you tell premium quality cream?
Shows a volume increase of at least 80%, there is no serum separation 18°C after 1h
What type of emulsion is butter>
An emulsion of water-in-oil
Describe the phases of butter
It has a continuous phase of liwuid milk fat in which are trapped water droplets, crystallized fat grains and air bubbles.
How is the phase inversion in butter achieved?
With hydrophilic emulsifiers (lauroyl glutamate)
What is the butter content of fat, water, and fat-free solids?
Butter is made up of 81-85% fat, 14-16% water, 0.5-4.0% fat-free solids (and 1.2% NaCl in the case of salted butter)
What are the 3 types of butter?
- Butter from sour cream (cultured-cream butter)
- Butter from non-soured sweet cream (sweet cream butter)
- Butter from sweet cream, which is soured in a later stem (soured butter)
What is churning?
- It involves agitating the cream or milk vigorously at a temperature whereby milk fat is partly solid and partly liquid (~50°C)
- Further agitation causes the crystals to solidify and separate out from the milk
What is meant by a water in oil emulsion?
The fat forms the continuous phase with the droplets of the aqueous phase trapped in it
Why is the cooling step important in butter making?
It allows the fat to crystallize
How is buttermilk made?
Once a large amount of air has been incorporated into the cream to form whipped cream, Continued agitation turns the whipped cream coarser, and eventually, the fat forms semi-solid butter granules, which separate sharply from the liquid phase
How is Ghee made?
Made by melting butter at a slightly elevated temperature with stirring. The melted butter forms a yellow-golden liquid with white froth on top of it. Further stirring causes the froth to break up while the liquid becomes more intense yellow in color. This liquid forms on top of solid sediment which is removed and then the liquid is cooled to solidify the ghee
What are some constituents of ice cream?
- Whole milk
- Skim milk
- butter oil
- Condensed and/or dried milk products
- Fruit and fruit ingredients
- Approved food colours
How is ice cream pasteurized?
Mix ingredients ad pasteurize at 170°C for 10-30 mins or 80-85°C for 10-20 seconds
Why is ice cream pasteurized?
This homogenizes milk which breaks down fat globules into smaller sizes. This is importnat to increase viscosity of the product.
Why is air introduced to ice cream ingredients?
To increase the volume of the product
What temperature is ice cream cooled to after pasteurization?
~4°C to help increase viscosity
What temperature is soft ice cream frozen at?
At what temperature is hard ice cream frozen?
What does a typical ice cream formulation recipe consist of?
- 10% milk fat
- 11% milk solids-nonfat
- 14% sucrose
- 2%glucose syrup solids
- 0.3% emulsifiers
- 0.3% thickeners
- 62% water
Why are thickeners used in ice cream?
Thickeners (mostly polysaccharides) increase the viscosity of the product
Why are emulsifiers important in ice cream?
Prevent the fat globules from aggregating during the freezing steps and frozen storage
LOOK AT SCHEME FOR MAKING ICE CREAM
How is the sour flavour of fermented dairy products achieved?
Due to the acidification of lactic acid produced into the product from the metabolic activity of lactic acid bacteria
Which microorganisms are commonly used in fermented dairy products?
Often members of the genera Lactobacillus, Lactococcus, Leuconostoc, Pediococcus and Streptococcus. Although other bacteria, yeasts, and molds may also be involved.
Which pathways lead to the production of lactic acid?
Glycolytic and Pentose phosphate pathway
What is homofermentation?
When fermentation proceeds via the glycolytic pathway to form lactic acid exclusively
What is the glycolytic pathway?
- Lactose is made of glucose and galactose, which go through the glycolytic pathway and form pyruvate
- Galactose can turn into glucose, which then goes through the pathway and together 4 pyruvates are formed- the pyruvates then form 4 lactic acids
What is heterofermentation?
When the fermentation proceeds via the pentose phosphate pathway with the formation of multiple products (lactic acid, acetic acid, ethanol, CO2)
What is an example of a heterofermentative bacteria?
Leuconostoc mesternides (LM)
What results from fermentation via leuconostoc mesternides (LM)?
The products from a molecule of glucose are 1 molecule of lactic acid, 1 molecule of ethanol or acetic acid and CO2
How is fermentation used as a method of preservation?
Lactic acid formed lowers the pH of the product, which is not conducive to the growth of some microorganisms and also deactivates some enzymes
In addition to lactic acid, what else is formed during fermentation?
Various aroma substances are formed from proteolysis and lipolysis
What are some examples of fermented dairy products?
- Sour milk
- Sour cream
Which fermented dairy product has the lowest lactic acid content?
Which fermented dairy product has the highest lactic acid content?
How is sour milk obtained?
Obtained by spontaneous souring fermentation of milk or by addition of various lactic acid-producing bacteria such as leuconostoc cremoris, lactococcus lactis, L. cremoris, L. diacetylactis to milk
What happens when the pH of milk reaches 4-5?
Casein begins to coagulate
Why is milk often blended with powdered milk when making sour milk?
To increase the total solids content
What is natural buttermilk?
Refers to the left over liquid after churning of butter, hence contains little or no fat
How is cultured buttermilk produced?
Produced by addition of bacterial cultures, specifically streptococcus lactis, to pasteurized skim or partly skimmed milk. The resulting product is thicker, more sour, and more bubble than regular milk
Which bacteria is used to produce cultured buttermilk?
What is the difference between cultured buttermilk and regular milk?
Cultured buttermilk is thicker, more sour, and more bubble than regular milk
How is sour cream produced?
Produced by addition of streptococcus lactis to light cream followed by fermentation at 22°C until the concentration of lactic acid reaches ~0.5%
How is yogurt made?
Produced by adding LAB starter culture to pasteurized homogenized milk (often containing added milk solids-non fat and sugar). Followed by an incubation at 42-45°C for about 3h
What is the final pH of yogurt?
How much lactic acid does yogurt contain?
0.7-1.1% lactic acid
What is acidophilus milk?
- A lower concentration of lactic acid (0.5-0.7%)
- Produced by incubation of pasteurized milk with lactobacillus acidophilus at 37-38°C
What is active culture yogurt?
After the fermentation, yogurt is heated or chilled to stop the fermentation process. If it is chilled, the bacteria remain active and it is called ‘active culture yogurt’
Why is gelatin added to yogurt?
Gelatin or skim milk powder is often added to yogurt to thicken it or mask its sour taste.
FLOW CHART FOR YOGURT
What is kefir?
Kefir is a sparkling, slightly alcoholic milk beverage that is indigenous to Turkestan
Which microorganism in kefir is responsible for alcoholic fermentation?
What are kefir grains?
Particles of clotted milk plus the kefir microflora, which resembles cauliflower heads when wet and brownish seeds when dry
How much alcohol does kefir contain?
How much lactic acid does kefir contain?
What are the basic steps of cheese making?
Curdling the milk, followed by removal of whey, and then ripening of the curd in the presence of special microflora
What are some different ways that cheeses can be classified?
- Based on the milk source
- Based on the mode of curd formation (acid or rennet/chymosin or a combination)
- Based on texture, consistency, or moisture content (extra hard, hard, semi-hard, semisoft, or soft)
- Based on fat content (double cream, cream, whole-fat, fat, semi-fat, low-fat, skim)
What is the water content of extra hard cheese?
What is the water content of hard cheese?
What is the water content of semi-hard cheese?
What is the water content of semisoft cheese?
What is the water content of soft cheese?
What is the fat content of double cream cheese?
What is the fat content of cream cheese?
What is the fat content of whole-fat cheese?
What is the fat content of fat cheese?
What is the fat content of semi-fat cheese?
What is the fat content of low-fat cheese?
What is the fat content of skim cheese?
What is the first ingredients added to cheese?
CaCl2, Nitrates/nitrites, and lysozyme
What is mesophilic bacteria?
Do not have a high tolerance for heat (ex. Streptomyces crenoris, Streptomyces lactis, Streptomyces diacekylactis)
What are thermophiles?
More heat tolerant and can withstand heat treatments above 40°C up to 60°C (ex. Lactobacillus bulgaricus, Streptomyces themophilus)
What characteristics must cheese cultures have?
- Capacity to utilize lactose to produce lactic acid
- Capacity to breakdown proteins during the ripening process to produce low molecular weight peptides and free amino acids to impart flavor
- Some are able to produce CO2 and propionic acid
Give of an example where CO2 production is important in cheese making?
Aside from causing curdling, why is lactic acid important?
It curtails growth of undesirable bacteria in the cheese
What is the difference between using enzymes vs acids as a coagulating agent for cheese making?
If you use enzymes, you will get a relatively lower yield than if you use acids
If the cultures added to the cheese don’t produce enough acid, what can you do?
Deliberately add acids such as delta-gluconolactone, lactic acid, propionic acid) to achieve coagulation
What is the desired ratio of protein:fat in cheese?
How much protein is recovered with enzyme coagulation?
How much protein is recovered with heat-acid coagulation?
What is syneresis?
- After the curd has attained the desired firmness, it is cut into cubes and heated with gentle stirring; the pieces begin to shrink and expel the whey
- The heating causes the protein matrix to shrink due to increased hydrophobic interactions and also increases the rate of fermentation of lactose to lactic acid
What determines the final pH of the cheese after curing?
The final moisture content of the curd determines the residual amount of fermentable lactose and thus the final pH of the cheese after curing
What happens during the ripening of cheese?
During ripening, degradation of lactose, proteins and fat proceed by the action of ripening agents, such as bacteria and milk enzymes (proteases, lipases, added molds/yeasts, even environmental contaminants)
How is flavor and texture imparted during ripening?
Breakdown of proteins/fats into free amino acids, low molecular weight peptides, free fatty acids all to impart flavor and texture
How is a ripened cheese product stored?
In appropriate packaging material (paper plastic wraps) and stored at temperature between 10°C-15°C in a controlled environment with RH of ~80%
What are the 2 stages of coagulation of casein after rennet is added?
- Transformation of casein to para-casein
- Precipitation of para-ccasein in the presence of Ca++ ions
Where does rennet come from?
Extracted from the fourth stomach of young calves
Where do pepsins come from?
Bovine and porcine pancreas
What are the 3 main types of substitutes for the animal enzymes?
- Coagulating enzymes from plants
- Coagulating enzymes (acid proteinases) from microorganisms
- Recombinant chymosin
When does production of lactic acid stop?
When all lactose in the cheese has been fermented
What is the purpose of adding salts of calcium and phosphorus to cheese?
Increase the firmness of the curd
Why is proteolysis important in cheese making?
The original proteases of the ilk and those of the bacteria in the starter culture, together with rennet enzyme, cause decomposition of the protein, giving rise to flavor and aroma compounds
What is the purpose of propionibacterium?
Added as a starter culture to products like swiss cheese, convert lactic acid into propionic acid, acetic acid and CO2
How are holes/eyes created in cheese making?
The CO2 gas initially is dissolved in the moisture phase of the cheese and when the solution becomes saturated the gas is released and collects within pockets in the ripening curd, resulting in the formation of holes/eyes
Why is CO2 injected into cheese milk?
Sometimes done to lower the pH (usually by 0.1-0.3 pH units) and shorten coagulating time
What is saltpeter?
NaNO3 or KNO3
Why is saltpeter added to cheese?
Saltpeter is added in appropriate doses to cheese to control growth of undesirable bacteria and microorganisms of the genus Clostridium
How is the saltpeter requirement in cheese making reduced or eliminated?
If milk is pre-treated by processes such as microfiltration, the saltpeter requirement can be substantially reduced or even eliminated
Why is calcium chloride added to milk when making cheese?
CaCl2 is added to milk at a level of ~5-20g per 100kg of milk to achieve a constant coagulation time and firmness of the coagulum
What could happen if excess calcium chloride is added to cheese?
Could make the coagulum too hard and difficult to eat
Why is disodium phosphate added to cheese?
If legally permitted, disodium phosphate (NaPO4) may be added to milk (before the CaCl2) to increase the elasticity of the coagulum as in the production of low-fat cheese
Which colorants are often used in cheese making?
Coloring agents such as carotene and orleana are used to correct seasonal variations in countries where coloring is permitted
Why is green chlorophyll used in cheese making?
Green chlorophyll (contrast dye) is also used in some cheeses (blue-veined cheese_ to obtain a ‘pale’ color as a contrast to the blue mold
How is cheese molded (shaped)?
After all free whey has been removed it is transferred directly into a mold (granular cheese) or by pressing it into a block that is cut into pieces o suitable size for placing in molds. These molds are then placed in a pneumatic or hydraulic pressing system, where pressure is applied to the curd to assist final whey expulsion and texture development
Why is salt added to the cheese curd?
- Salt causes more moisture to be expelled, both through an osmotic pressure effect and a salting-out effect on the whey proteins
- It also affects the consistency of the cheese as well as the bacterial processes that take place during ripening
How is salt added to cheese curd?
Salt is applied either by dry salting or brine salting
How is salt brining done to cheese curd?
After the molding of the curd, it is kept in a container with brine or salt concentrations of up to 23% at 10-14°C, typically for 1-3 days
What does the amount of salting of a cheese curd depend on?
- The salt content tpical of the type of cheese
- The size of the cheese- the larger it is, the longer it takes
- The salt content and temperature of the brine
- The rate or salt penetration and absorption
How does salt penetrate the cheese curd?
Salt penetrates into the curd via capillaries that criss-cross the curd
what are the main structural elements of ice cream?
ice crystals, air bubbles, fat globules, and aggregated fat globules. The fat is mostly attached to air bubbles. The function of the air bubbles is threefold: they reduce the density, soften the product, and prevent a strong cold sensation during consumption.
*TRUE OR FALSE: Oxytocin is a growth hormone given to cows to increase milk production.
*TRUE OR FALSE: The term homofermentation refers to a yogurt-making process in which milk is homogenized prior to addition of a starter culture.
- A type of lactic acid fermentation in which sugars (such as lactose, glucose, pentose) are converted entirely, or almost entirely, into lactic acid.
*The addition of water to milk at the farm or during transport is detected at the processing plant by checking the ________.
*TRUE OR FALSE: Trypsin is the enzyme in rennet that is responsible for curd formation in cheese production.
*Skim milk contains approximately ____% solids.
*In the production of some cheeses, the milk is homogenized prior to addition of the starter culture. The main purpose is:
to enhance lipolysis during ripening
*TRUE OR FALSE: If milk is heated to not less than 71.7°C for no less than 6 seconds, it has undergone adequate homogenization.
*Name 3 substitutes for animal sources of proteases such as rennet in cheese making.
- 1. coagulating enzymes from plants
- 2. coagulating enzymes acid proteinases from microorganisms
- 3. chymosin produced by recombinant DNA technology (commercially available)
*Explain the significance of orotic acid
Orotic acid is the only component in the acid-soluble nucleotide fraction in cow milk. Orotic acid concentration in cow’s milk varies considerably in dairy cows, and this is due primarily to cow-to-cow variation. Thus, orotic acid is used as one of the reliable indices of the proportion of milk in foods.
*TRUE OR FALSE: In raw milk the average diameter of the casein micelles is smaller than the average diameter of the fat globules.
*Which vitamin is added to milk in Canada?
*TRUE OR FALSE: The WHO has recommended an upper limit on the amount of D-lactic acid that a person consumes in milk per day, depending on body weight.
*TRUE OR FALSE: Raw cow's milk is ~3.7% fat and ~12.7% solids-non-fat
False, 3.9% fat and 7.8% solids-non-fat
*During curd formation, what is highly detrimental in relation to the quality of the cheese ultimately produced?
introduction of bacteriophages
*During cheese ripening, the production of _________ is highly undesirable.
*Describe the biochemical processes that occur during cheese ripening (curing).
- Cheese components are modified biochemically to varying extents during curing.
- Lactose: Lactose is degraded to lactic acid by homofermentation. This involves the initial hydrolysis of lactose into glucose and galactose. Galactose is epimerized to glucose; and 1 mole of glucose in metabolized via the glycolytic pathway into 2 moles of pyruvate. The 2 moles of pyruvate are subsequently reduced to 2 moles of lactic acid. Homofermentation thus yields 2 moles of ATP per mole of glucose consumed. Examples of homofermentative bacteria include Lactococcus, Enterococcus, Streptococcus and Pediococcus.
- Fat: Milk fat is broken down by lipase and the type and degree of the breakdown depend on the microflora and the lipases involved in cheese ripening. In most types of cheese, as little lipolysis as possible (e.g., cheddar) is a prerequisite for good aroma, while in other cheeses extensive lipolysis is needed (e.g., Roquefort, Gorgonzola, and Stilton). The extent of lipolysis is strongly influenced by whether the milk has been homogenized.
- Proteins: Milk proteins are degraded by proteolytic enzymes into low molecular weight peptides and amino acids. The degree of proteolysis depends on both the moisture and salt contents of the cheese. Among the amino acids released, glutamic acid is of special importance to cheese taste. Ripening defects include the formation of bitter peptides and undue texture softening. Amino acids (such as histidine and tyrosine) released by proteolysis may be transformed further by decarboxylations into their corresponding amines (a.k.a., biogenic amines).
What are the factors that govern the extent of aggregation of caseins in milk to form casein complexes?
Why is human milk preferred to cows milk for infant feeding, eventhough human milk is lower in proteins and higher in sugars?
- Human milk is higher in many nutrients that infants need such as iron (many babies fed cows milk become iron deficient)
- Human breast milk also contains antibodies that the baby needs to protect against diseases
- Human milk contains microflora to develop in the babies colon