Exam 1 Flashcards
1
Q
Cows in U.S.
A
- Overall the number of cows has declined significantly since the 1940’s
- In recent years the number has held steady currently about 9.2 million cows in the US
- Since the number of cows has decreased or remained constant, then the amount of milk produced per cow has increased
2
Q
Milk yield from cows in US
A
In 2010 the average cow yielded 21149 pounds of milk (2460 gallons)
Note that in 1955 the average cow gave 5500 pounds of milk (639 gallons).
3
Q
Reasons for milk yield increase
A
Record keeping-DHIA (keeps records on individual cows-fat, solids, yield, somatic cells, breeding issues, etc).
Loss of marginal producers
Better nutrition-TMR
Selective breeding-Artificial insemination, breeding for yield and for components—leading to improved genetics
4
Q
Top 5 Milk producing states:
A
Ca, WI, ID, NY, PA
5
Q
PA milk facts
A
Ranks 5th in milk production
Total production is 10,734 million pounds
Value of milk shipments $1.95 Billion which was 30.3% of all farm receipts
6
Q
Bulk tank
Holds 6000gal of milk
A
- The milk may also pass through a cooler (plate or tube) and a filter to remove debris prior to entering the bulk tank.
- The milk should be kept as cold as possible but should not be allowed to freeze (ice crystals can lead to rancidity and significant freezing can lead to protein stability issues)
- In a “typical” operation, the bulk tank is sized to accept 2-days worth of milk and pick up from the bulk tank is “Every other Day”
- The job of the transport driver is to determine the amount of milk in the tank (often done with a calibrated “dip stick”, take representative samples for chemical and microbiological analysis, and transfer the milk to the truck.
-Important to note that samples are taken for antibiotic analysis at this point
7
Q
Types of milk
A
Milk from a single cow
Milk from a single BTU (bulk tank unit)
Comingled milk (milk from more than one BTU
8
Q
Milking operation
A
Required:
- Temperature must be less than 45F (40 or below is better)
- Antibiotic analysis must be free of detectable antibiotic by accepted methods
Non-required:
Odor Free of off-odors
Visual should not contain visible floating matter
Acidity Should meet TA or pH specifications
DMCC Should be low (generally no more than 1 or two clumps)
Added water Should have a freezing point within the normal range (-0.522C)
It is common for a company to have specific standards in place that exceed the minimums required by the state or federal government.
9
Q
Grade “A” Raw milk
A
Temp: Cooled to 7oC or less within 2hrs of milking
Bacterial limit: individual does not exceed 100,000/ml
Commingled: does not exceed 300,000/ml
Drugs: No pos. results
Somatic cell count: Ind. not exceed 750,000/ml
10
Q
Grade “A” Pasteurized milk
A
Temp: Cooled to 7oC or less within 2hrs of milking
Bacterial limit: 20,000/ml
Coliform: not exceed 10/ml
Phosphatase: less than 350mu/L for fluid and less than 500 for other milk products
Drugs: No pos. results
11
Q
Acidity in milk
A
The Total acidity of milk is due to a number of factors and can be broken in to apparent and developed acidity.
The apparent acidity of the product is the acidity prior to fermentation or addition of acid.
The developed acidity is the component of Total acidity that results from addition of acid or from the action of microorganisms.
The apparent acidity of milk is not primarily due to lactic acid, but rather to carbon dioxide, proteins, and other materials natrually in the milk.
It is important to recognize that the apparent acidity of the product will change if the level of these components is altered. Thus, when preparing a formulated or concentrated product like yogurt, where the MSNF is increased from 9 to 12 or 14 percent, the apparent acidity of the initial prodct will increase. Thus, if the product at time zero has an acidity of 0.2 and after fermentation an acidity of 0.5, there is only 0.3% developed acidity (lactic acid) in the sample.
12
Q
Determining microbial
A
Standard Plate Count (SPC) Psychrotrophic Bacterial Count (PBC) Preliminary Incubation Count (PIC) Coliform Count DMCC
13
Q
Screening for Mastitis
A
Screening important because it indicates illness in the dairy cow
-effects rennet coagulation time and
14
Q
Mastitis Detection Methods
A
California mastitis test (CMT) (based on release of DNA from somatic cells-- addition of NaOH, Lysis of cells & release of DNA) paddle Wisconsin mastitis test (WMT) tube DMSCC Coulter counter Catalase
15
Q
Screening for Antibiotics
Microbial method 1
A
Bacillus stearothermophilus disk assay -dip disk in milk -place on seeded agar -incubate -examine for zones Primary disadvantage is time required to complete the test
16
Q
Screening for Antibiotics
Microbial method 2
A
Delvotest-P® and Multi test
based on rapid growth and acid production by B. Stearothermophilus var. calidolactis
Bromocresol purple———-> Yellow
-is faster then Disk assay, but still requires 3hrs for metabolic activity
17
Q
Charm test
A
Based on specific irreversible binding of antimicrobial drugs with receptor sites on microbial cells
These test come in various formats
Can be used on composite samples
Can be used cow sideSo, if a sample is free of antibiotic you would expect a “high count” and if it contains antibiotic you would expect a “low count”.
18
Q
Detection of Added Water
A
-The freezing point of milk is nearly constant
-Addition of water to milk will alter the freezing point
-By measuring the change in freezing point the amount of water added can be determined
% added water = (T - To)/T * 100
19
Q
Biologically milk is:
Chemically:
Legally:
A
Liquid secreted by female mammals to nourish their young
A complex mixture of organic and inorganic substances consisting of water, fat, a carbohydrate, proteins, minerals, gasses, bacteria, enzymes and vitamins.
Milk is the lacteal secretion, practically free from colostrum, obtained by the complete milking of one of more healthy cows which contains not less than 8.25% milk solids not fat and 3.25% milk fat.
20
Q
Constituents of milk
A
Water, Fat, Protein, Carbs, Ash/mineral
determined through proximate analysis
21
Q
Water in milk
A
Avg: 87.0%
Range: 85.3-88.7%
Most abundant component of milk
Acts as solvent and dispersent
Physiologically it provides moisture to young
Water is Water is Water
22
Q
Fat in milk
A
Avg: 4.0%
Range: 2.5-5.5%
23
Q
Protein in milk
A
Avg: 3.25%
Range: 2.3-4.4%
Casein: 2.6%, 1.7-3.5%
Whey Protein: 0.6%, 0.4-0.8%
24
Q
Lactose in milk
A
Avg: 5.0%
Range: 3.8-5.3%
-Limited water solubility
-Involved in browning reactions (reducing sugar)
-Energy source for microorganisms use to ferment milk
-Depresses freezing point of dairy products
-Lactose is the primary carbohydrate of milk.
-As shown here, it is a disaccharide composed of glucose and galactose.
-On a scale where sucrose is 100, lactose is a 20 with respect to sweetness. Thus, although it contributes some sweetness to dairy products, it is not generally considered a sweetener.
-Many people are deficient in the enzyme Beta-galactosidase (Lactase) required for the efficient metabolism of lactose. These people are said to be lactose intolerant as shown in the following cartoon.
25
Ash in milk
Avg: 0.75%
Range: 0.65-0.8%
26
Parts of Milk
Water
Total Solids
-MSNF
-Milk fat
27
Mutarotation in milk
At higher temperatures the reaction completes quicker and reaches an equilibrium between alpha and beta. At lower temps it is a much slower reaction. This effect solubility as the beta form is more soluble than the alpha version. pH also has an effect of the rate of mutarotation Very low pHs and near neutral pHs result in higher k (reaction constant). pH of milk is ~6.7
28
Lactose Reactions
Lactose participates in a number of important reactions in milk and in other foods where milk or purified lactose are used as ingredients.
Maillard browning (reducing sugar and amino group)
Caramelization (High heat reaction, results in formation of brown color compounds as well as flavor compounds).
Hydrolysis (lactose hydrolysis is usually brought about ezymatically, difficult with acid)
Lactulose (this is an isomerization reaction of lactose that occurs during heating of milk.
The level of lactulose present in the milk can be used as an indicator of the heat treatment the product has received (LTLT, HTST, UHT) and can even be used to indicate the degree of heat treatment within a category.
29
Crystallization of Lactose
Solutions of lactose can be supersaturated prior to spontaneous crystallization
However, the level of super-saturation must be quite high for “spontaneous” crystallization to occur
Lactose crystals result in a defect known as “sandy”
30
Lactose Intolerance
Lack of digestive enzyme lactase
Lactose intolerance is a reslt of a deficiency n the enzyme B-galactosidase (lactase).
Since lactose is not metabolized in the ???? It then passes into the lower intestine where gas forming bacteria are able to ferment the lactose causing bloating a flatulence.
In addition, the unmetabolized lactose increases the osmotic pressure within the cut causing an efflux of water that can manifest as diarrhea.
31
Milk Fat
The fat system in milk is extremely complicated and is responsible for a number of flavor and structural attributes of dairy products.
Although the lipid system is complicated, approximately 98% of the fat in milk is present in the form of Triglyceride.
This slide reminds you of the general structure of a triglyceride and shows a chemical structure of a mixed triglyceride. Most of the triglycerides in milk are mixed I.e. they contain more than one FA type.
The second chemical reaction depicted on this slide is lipolysis or hydrolytic rancidity. This reaction occurs when FA are cleaved off the glycerol backbone by the enzyme lipase. Since milk contains a relatively high proportion of low MW FA, lipolysis of milk quickly results in detectable off flavors.
32
Milk Fat cont.
Chemically, milk fat is a mixture of different triacylglcerides
Exists as tiny droplets called globules
0.8 to 10 mm (micrometers)
(1 mm is 1/25,000 of an inch)
the average globule is 3-4 mm
A single drop of milk contains 100 million globules
33
Lipids of Milk
Lipids are materials that are soluble in non-polar organic solvents and insoluble or sparingly soluble in water.
Milk fat is a complex lipid system composed primarily of triglyceride.
Point out that x bar is the aggregate carbon number and that y bar is the aggregate bouble bond number within a single triglyceride.
Look at the percentage of each component in milk fat. Note that milk is 98.3% Triglyceride. Note the dominant phospholipids are Lecithin and ethanolamine. These can serve as natural emulsifiers (so can mono and diglycerides).
Point out unsaponifiable lipids note the cholesterol content. (0.30%)
34
Fatty Acids in milk
The melting point of the inidvidual FA present in milk varies from –8C to 70C.
This indicates that at normal processing and storage conditions, milk fat will be in a liquid-crystalline state. The L-C states plays a role in structure development in a variety of products.
Milk contains a high proportion of C4-C10 Fatty Acids. These acids are known collectively as the short chain fatty acids.
Milk also contains a high proportion of “volatile” fatty acids. C4 (Butyric),C6 (Caproic) and C8 (Caprylic) are considered volatile.
The relativle colubility of the fatty acids in milk differs greatly. In general the short chain fatty acids are much more soluble than the longer fatty acids. Why do you suppose this is true?
Note the percentage of particular FA in the 3 position of the triglyceride. This distribution is by no means random. The fact that the shorter chain FA are more common at SN3 is a of concern when considering rancidity. Since the Short Chain FA are more flavorful, there selective cleavage from the backbone leads to rancidity quickly in dairy products.
Milk fat does contain some diene and polyene fatty acids
Keto and hydroxy acids are important flavor precursors
3-ketoacids>>>Methyl ketones on heating
Hydroxy acids.>>>lactones on heating
35
Milk Fat Globule
The fat is coated with a “membrane” as it is secreted out of the lactating cell.
This so called milk fat globule membrane imparts a certain stability to the milk fat with respect to attack by lipase as well as partially stabilizes the milk fat in milk serum emulsion.
36
Rancidity
```
Oxidative Rancidity
-Covered in detail in other courses
-Rxn of Unsaturated FA and Oxygen
Hydrolytic Rancidity
-Release of FA from the glycerol backbone
```
```
Lipoprotein lipase
-spill over from mammary tissue
-inactivated by pasteurization
Lipase from psychrotrophs
-often heat stable
Others
-May be added with rennin
```
37
Milk Proteins
Milk contains about 3.2 percent protein.
The major protein classes found in milk, the casiens and whey proteins, are differ markedly.
Casiens have little secondary and tertiary structure, but have very complex quarternary structure.
The whey proteins are more “traditional” globular proteins.
In addition to there role in nutrition, proteins are very important structure forming molecules (gels) and are also important surfactants that aid in in emulsion stability in both dairy products and non-dairy products. In fact, caseins are often added to products for there emulsifying ability.
38
Types of Milk Proteins
```
Bovine Milk contains about 3.2% protein
80% Casein
15% Whey Proteins
5% Non-protein Nitrogen
(Remember that nitrogen is used to estimate protein content).
```
The NPN of milk consists of Urea, a few free amino acids and partially hydrolyzed proteins (this fraction is often called the proteose-peptone fraction).
39
Caseins
Caseins unstable at pH 4.6 (precipitates/insoluble)
Caseins are stable to heat.Heat insensitive (T<120oC)
Caseins are sensitive to Ca.
Have a low degree of 2, 3 structure, but a high level of quartenary structure. Spontaneously forms aggregated structures
A heterogeneous group of phospho-proteins made up of: as1, as2, b and k caseins
-ratio is 40:10:35:12
Occur as micelles or organized aggregates
Responsible for coagulation of cultured milk products
About 26 g per kg of milk
40
Whey Proteins
Remain in solution after precipitation of caseins at pH 4.6
Lactoglobulin, Lactalbumin, Bovine serum albumin (BSA), and immunoglobulins (typical globular proteins)
Can heat denature and may form aggregates (high level of 3 structure)
About 6.3 g per kg of milk
Heat sensitive (T>~70oC)
41
Casein Micelle Structure
This is a model of casein micelle structure. Remember each micelles is made up of about 104 molecules of casein and that each submicelle is made of about 25 casein proteins therefore, each micelle is composed of roughly 400 submicelles arranged in a spherical orientation.
Note that protruding peptide chain of K casein contains a carbohydrate moiety.
Note also that the submicelles on the “inside” are poor in k casein while the submicelles on the surface are “rich” in k casein.
Remember the ratio of caseins in the micelle is 4:1:4:1.6 (thus each submicelle does not have to have a k casein).
Note that during formation if two of the “hairy” submicelles approach each other “hair on” there is a steric repulsion due to the side chains.
Micelles are voluminous and contain 2-2.5 ml of water per gram of dry case (4 ml per gram if you account for the hairy layer). This indicates a fairly open structure.
42
Instability Mechanisms
There are several coagulation mechanisms used to make milk gels. The most commercially important are acid and enzymatic coagulation.
Heat-chemical changes to micelles, not reversible
Acid (ph 4.6)- CCP dissolve, partly reversible
Rennet- Casein split, not reversible
Excess Ca+, more CPP, is reversible
43
Rxn of Milk Proteins
```
Proteolysis
Destruction of primary structure
Caused by enzymes
Milk plasmin (native to milk)
Bacterial Enzymes (Psychrotrophs)
Denaturation
Heat
Acid
```
44
Minerals (ash)
Milk is high in Ca, P
Milk lacks Fe, Cu, I and Mn
Milk salts are involved in:
Age gelation of concentrated milk products
Feathering of coffee cream
Whipping of ice cream during freezing
Hardness and syneresis in cultured dairy products and cheeses
45
Composition & Distribution of salts
Take a look at the major cations and the major anions of milk. Note that Ca and K are the two most prevalent cations (see the average column (mg/100g) and that the major anions PO4, Citrate and Cl.
Note the distribution of the cations between the serum phase and the casein micelle. The most interesting observation is that only 32% of the Ca and only about 47% of the phosphate are present in the serum phase. If it is not in the serum phase, than it must be associated with the micelle.
The molar concentration data presented in the last column supports the idea that these two minerals (Ca and PO4) are present at high concentrations in the micelle. This suggests the two minerals may play a role in either or both micellar structure or stability.
46
MIlk Composition Terms
Total Milk Solids = (Milk -Water) = (Fat + Protein + Lactose + Ash)
Milk Serum = (Milk - Fat) = Skim Milk
Milk Solids Not Fat = (Total Solids-Fat) = Non Fat Dried Milk
47
Variations in Composition of Milk May Be Due to:
```
Species
Breed
Individual
Stage of lactation
Stage of milking
Interval between milkings
Mastitis
Feeds and feeding
Season of the year
Volume of milk produced
BST
```
48
Variation b/w breeds
Holstein cows produce the largest amount of milk. Another was to compare the yields would be to look at the total amount of component:
Breed Fat Protein
Holstein 661 560
Jersey 602 463
Guernsey 614 474
Thus, the holstein “wins” on both accounts.
49
Properties of Milk
Taste and Odor
Properly produced milk has a bland, slightly sweet flavor and a faint characteristic odor (described as milky)
Both taste and odor are affected by feed of the cow, improper cleaning of utensils, development of bacteria, exposure to copper and iron, barn ventilation, physical condition of the cow and mastitis.
Color
- Normal milk is yellowish white due to the presence of casein and emulsified fat.
- Yellowish color is imparted by carotenoids in the fat, but the whey is yellowish green due to the presence of riboflavin
50
Properties of milk
```
Fp: -0.522oC
Bp: 100.28oC
Sp. gravity: 1.032
Density: 1032kg/m^-3
pH: 6.60+/-0.2
TA: 0.16%+/-0.02
```
51
Density of Milk
1/density milk = E (mass fraction of component x / apparent density of component x)
52
Acidity of Milk
Acidity of milk
Expressed as either pH or TA
pH measure H+ concentration
TA measures (or is intended to measure) the amount of lactic acid produced in the system
TA actually measures the amount of OH- required to move pH from 6.6 to ca. 8.3
53
Milk as a Substrate for Microbes
```
Nutrient rich
-Vitamins, protein, carbohydrates
-Lacks free nitrogen
Oxygen
-In general not suitable for strict anaerobes
Natural Inhibitors
-Immunoglobulins
-Lysozyme
-Lactoferrin
-Lactoperoxidase isothiocyanate system
```
54
Microorganisms in Raw Milk
Milk is sterile when secreted from healthy cows
Contamination occurs during milking:
1) within the udder
2) exterior of the teats and udder
3) milking, transport, and storage equipment
Animal, Environment, Milker, Dairy Utensils, Tank trucks, Transfer lines, Processing Equipment
55
Microorganisms in Raw Milk
- Milk is collected from the farm, transported, and held at low temperatures.
- These conditions 5 – 10°C (40 – 50°F) allow cold-tolerant (psychrotrophic) organisms to grow. -Inadequately cleaned equipment is the main source of psychrotrophs in milk.
56
Classification of Microorganisms by Growth Temperature
Psychrotrophic
Mesophilic
Thermophilic
Thermoduric
57
Psychrotrophs in Raw Milk
```
Mostly Gram-negative rods
Mainly spoilage genera
-Pseudomonas (~ 50%)
-Alcaligenes
-Flavobacterium
-coliforms
Some pathogens
-Yersinia
-Listeria
```
58
Pathogenic Bacteria Found in Raw Milk
```
Staphylococcus aureus no growth @<6C does not survive pasteurization
Salmonella Temp? & no
E.cli yes, no
Yersina enterocolitica yes, no
Campylobacter no, no
Clostridial spp no, yes
Bacillus cereus yes, yes
Listeria monocytogenes yes, no
```
59
Control of Microorganisms in Raw Milk
```
Keep the microbes out
Clean and sanitize the udder
Keep equipment cleaned and sanitized
Control temperature
Minimize storage time
Pasteurize ASAP
```
60
Microorganisms in Pasteurized Milk
* Post-pasteurization contaminants:
Mostly Gram-negative psychrotrophic rods
Primary reason for spoilage of pasteurized milk
* Bacteria that survive pasteurization
Mostly Gram-positive
Often are spore-forming
These bacteria are called thermoduric
61
Thermodurics in Pasteurized Milk
```
Thermodurics have the ability to survive pasteurization conditions 70 - 80°C (155 - 175°F).
Thermoduric bacteria:
-Bacillus
-Clostridium
-Micrococcus
-Streptococcus
-Brevibacterium
```
62
Spoilage Activities of Bacteria in Milk
Undesirable fermentation and acid production
Protein and lipid hydrolysis
Slime formation
63
Undesirable Fermentation of Milk
Bacteria may ferment lactose to produce acids and/or gases
Coliforms
Lactic acid bacteria
Clostridium
64
Protein and Lipid Hydrolysis of Milk
Natural milk lipases are inactivated by pasteurization.
Bacteria can produce proteases and lipases that are heat-stable.
-Pseudomonas
-Flavobacterium
-Bacillus cereus
-Clostridium
Psychrotrophs in raw milk may produce heat-stable proteases and lipases.
While most of the organisms will be killed by pasteurization, the enzymes will still be active.
Proteases may result in bitter or fruity flavors.
Lipases may result in rancid and soapy flavors.
65
Slime Formation
Some bacteria produce a “slimy” layer of polysaccharides
Spoilage by these bacteria results in “ropy” milk
-Alcaligenes
-Acinetobacter
-Escherichia coli
-Bacillus
May result in the formation of a biofilm, or a sticky matrix of “slime” on a surface.
Biofilms represent opportunities for cross-contamination.
66
Microbial Enumeration of Milk and Dairy Products
Bacterial Count Growth Conditions
“Total” Bacterial Count 32°C, 2-3 days
Psychrotrophic Count 5°C, 10 days
Thermoduric Count 32°C, 2-3 days after
heating sample to 63°C
for 30 minutes
Preliminary Incubation Incubate at 55°F then TBC
Direct Microscopic Count
"Total” Bacteria Count (Standard Plate Count)
Does not differentiate between organisms
Does not indicate source of contamination
Does not indicated effectiveness of processing
Typical range for raw milk: 1,000 to 300,000 CFU/mL
Thermoduric Bacterial Count
Most thermodurics can multiply in raw milk at ambient temperatures
High thermoduric counts indicate gross contamination from milking equipment
67
Microbial Enumeration of Milk and Dairy Products
| Coliforms
Coliforms:
-Gram-negative non-sporeforming rods
-Facultative anaerobe (grows with or without oxygen)
-Able to ferment lactose, with acid and gas formation, within 48 hours at 37°C.
Coliforms include Escherichia, Enterobacter, Citrobacter, and Klebsiella.
Coliforms are inhabitants of animal intestines and the environment.
Fecal coliforms are coliforms derived from the intestine of warm-blooded animals, and can grow at 44.5°C.
Escherichia coli is associated with the intestinal tract of humans. Some strains can be pathogenic (E. coli O157:H7).
Coliforms indicate potential underprocessing or post-processing contamination.
Enumeration of coliforms:
Violet Red Bile Agar (VRBA) and Brilliant Green Bile broth (BGB)
Petrifilm™
68
Legal Standards for Dairy Products
```
Raw Coming. milk Max: 300,000
Raw sing milk max: 100,000
Pasteurized milk max: 20,000 w/ 10Coliform.mL
Milk Prod 1: 50,000 10 coliform
Milk prod 2: 50,000 20 coliform
```
69
Formulas vs. Recipes
Recipe:
Specifies the amount of each ingredient to be used in a product (milk, cream, sugar, non-fat dried milk)
May specify the order of addition
May specify particular unit operations (mix, blend, etc)
Specifies the processing conditions
Formula:
Specifies the level of each component in a product (fat, protein, sugar…)
Processing conditions will be specified in another location
When comparing and contrasting recipes and formulas the obvious difference is that formula are INDEPENDENT of ingredient composition while recipes are DEPENDENT on ingredients having a specific compositions
The fact that formulae are independent of ingredients allows food scientists to deal with ingredient variability as well as provides opportunities to re-formulate using different ingredients to obtain a some benefit.
70
Ingredients vs. Components
Ingredient Components
Sugar Sucrose (sugar)
Liquid Sugar Sucrose, water
Skim Milk Fat, Protein, Lactose, Minerals, Water (note that this can be further sub divided as needed.
NFDM Fat, Protein, Lactose, Minerals, Water
Stabilizer Varies (may be a single component, or may be cut with sugar or salt)
71
Formulation
```
Variables
Consumer preferences
Technological considerations
Availability of ingredients
$$
```
72
Standardization
The process of recombining dairy ingredients to produce a product meeting a specific constituent analysis
This terms often means achieving a specific fat content
Methods: Blending--Mix cream and skim to achieve desired fat level, Continuous or “on the fly”
73
Blending
Skim milk of X% fat
Cream of Y% fat
Solve using “Pearson Square” or simultaneous equations
-Two Types of problems
--Preparation of definite amount of the desired product
--Preparation of an indefinite amount of the desired product
74
Pearson Square
Simple Method
Most often used for standardization
Useful for very simple mixtures
-One ingredient high and one low for a single component
It is important to recognize this system is only good for controlling one component
75
Examples of Serum Solids Content (SS)
```
Skim Milk
0% Fat
9% Non-Fat Milk Solids (protein, lactose, ash)
+ 91% Water
100% Total
```
```
Sweetened Condensed Skim Milk
0% Fat
25% Sugar
27% Non-Fat Milk Solids (protein, lactose, ash)
+ 48% Water
100% Total
```
40% Cream
100% Total
- 40% Fat
60% Serum
60% Serum
x 0.09
5.4% SS
76
Formulation Algebraic Method
```
Steps in the method
Identify components of interest
Prepare a total mass balance equation
Prepare component balance equations
Solve for the amount of each ingredient required (begin components found in only one ingredient)
```
77
Total Mass Balance
&
General Component Balance
The total mass balance is an equation that shows “the sum of the parts equals the whole”
Ex:
Skim + Milk + NFDM + Sugar + Stabilizer =100
Skim + Whole + NFDM + Sugar + Stabilizer = % Component* Amount of mix
78
Milk Fat content
Whole: 3.25
2% 2.00
1% 1.00
Skim <0.5
```
Creams:
Plastic ca 80
1/2 & 1/2 11.5
Light 18.0
Medium 25.0
Light whipping 31.0
Heavy Whipping 37.0
```
79
Flluid Milk Processing
Receiving operations are indicated as a pre-defined process (we discussed receiving operations in a laboratory exercise)
Clarification of the milk may occur at a receiving station or at the plant where the milk is received or may not be a separate unit operation at all. The process of clarification removes dense materials (dirt, debris, somatic cells) from the milk.
The next step in the process is pasteurization. The pasteurization step is THE KILL STEP in fluid milk process systems and is also the main critical control point in the process. It is important to recognze that pasteurization may actually span the separation, and homogenization processes (but it doesn’t have to).
During separation, the milk is seperated into skim milk and cream. Cream which will not be used in standardization is sent to a cream processing operation.
Cream & skim for fluid milk are standardized, homogenized, cooled, and stored.
80
Typical Receiving Operation
Truck arrives-> enter receiving bay--> open tank cover--> Odor & visual eval. (accept or reject)-->temp check (accept or reject)--> take samples-->antibiotic analysis (accept or reject)--> pH/TA(accept/reject)-->attach line receive milk--> wash and tag truck
81
Pumping
```
Centrifugal Pumps
-Most common
-Useful for low viscosity liquids
Positive Displacement Pumps
-Used for high viscosity fluids, metering applications
-Two Major Types
-Rotary
-Reciprocating
```
82
Definition of Pasteurization
The process of heating every particle of milk or milk product 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.
83
Purposes of Pasteurization
Destruction of vegetative pathogenic microorganisms present in the milk or dairy product. (C. burnetti)
Protection of public health
84
Time/Temp combos for Pasteurization
Vat (LTLT) HTHT
Milk 30min/145F 15sec/161F
MIlk Products 30min/150F 15sec/166F
Eggnog/ice mix 30min/155F 15sec/180F or
25sec/175F
85
Batch Pasteurization (VAT/LTLT)
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May be used by small plants
Useful for some small volume products
-Lower Temperature-Longer Time
More Chemical Changes
May be employed to impart specific attributes to a product (flavor, color, enhanced water holding capacity, etc.)
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Continuous Pasteurization (HTST)
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Basic Flow:
Balance Tank
Raw Regenerator
Timing Pump
Heating Section
Holding Tube
Flow Diversion Device/Leak detector
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Pasteurized Regenerator
Cooling Section
Vacuum Breaker
Pasteurized Storage
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Regeneration Efficiency
% regeneration: (Temp raw milk after regen - Temp of incoming raw milk) / (Pasteurization temp - temp incoming raw milk) *100
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Effects of Pasteurization
Improved keeping quality
- Microbiological Effects
- Destruction of spoilage bacteria
- Chemical Effects
- Inactivate Enzymes
- alkaline phosphatase, lipase, protease
- Denaturation of whey proteins
- Development of Cooked Flavor
- Free sulfhydral groups
- Formation of lactulose
Remember to indicate these are 2° effects and that the primary purpose is destruction of pathogenic microorganisms
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Microbiological Standards for Pasteurized Milk
SPC <10
Generally speaking, these standards are very high. Immediately following processing it is very difficult to detect m/o in good quality milk.
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Centrifugal Operations
Clarification
Separation
Bactofugation
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Clarification
The process of applying centrifugal force to a moving stream of milk in such a manner that dirt, debris, and leucocytes are removed
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Separation
The process of applying centrifugal force to a moving stream of whole milk in such a manner that the milk is separated into a fat-rich portion (cream) and a fat-deficient portion (skim milk).
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Bactofugation
High speed centrifugal removal of bacterial spores from milk (generally for cheese manufacture)
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Velocity of Sedimentation
| Separation
V = (d^2 (Pp -Pl)) / (18n) *g
OR * rw^2 (angular velocity* distance from axis of rotation)
Density of fat is about 980kg/m3
Density of serum about 1028kg/m3
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Standardization
The process of recombining dairy ingredients to produce a product meeting a specific constituent analysis
In the case of centrifugal operations this means achieving a specific fat content
Already discussed batch blending
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Blending on the fly
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Efficiently separate skim milk
0.04-0.07% Fat
Monitor fat content of cream
varies with
-fat content of milk
-temperature
-throughput
Blend desired amount of cream back into skim to achieve fat content
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Homogenization
Process of creating a permanent homogeneous emulsion of milk fat in serum by forcing a fluid dairy product under high pressure through a specially designed valve that causes the fat globules to be broken into particles so small that the forces of buoyancy are overcome by the viscosity of the serum phase.
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Homogenization Method
Most homogenization is accomplished using a TWO STAGE, valve homogenizer. This figure shows the valving of the system. The bulk of the system is a large, positive displacement pump, generally of the piston type.
Typical pressures are 1500 to 2000 psi on the first stage and 500 psi on the second stage.
The first stage reduces the particle size, the second stage breaks up clumps that form prior to coating with the new “membrane”
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Effects of Homogenization
Unhomogenized 0.2 to 20 um or larger
Homogenized <1um
Note wide distribution of fat globule sizes.
Note increase in number of fat globules
Reduction in mean globule size
Increase in number of globules
Increased globule density
Increase in surface area of globules
Increased viscosity due to increase in number of particles.
Whiter product due to more particles to disperse the light
Softer curd on acid coagulation
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Theory of Homogenization
Shear forces
Impact
Cavitation
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Negative Aspects of Homogenization
Milk can not be separated
Increased sensitivity to light induced flavor
Increased sensitivity to lipase
-this is important in the location of the homogenizer in a processing system
Decreased thermal stability of protein
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Changes in MFGM
4-6 X increase in MFG surface area
- Original membrane will not cover
- New membrane is composed of fragments of the old membrane and casein and whey protein
- Result is increased density of the MFG
- Aids in emulsion stability
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Legal test for homogenization
After 48 h of quiescent storage the fat test of the top 100 ml of a quart of milk, or equivalent portion in other volumes, shall differ by no more then 10% from the remaining, well mixed product.
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Storage of Product
After processing, the product is transferred to “pasteurized storage tanks” to await packaging.
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Packaging
Bag in a box
Waxed paper board (gable top)
Plastic “jug”
Consider light blocking materials
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Light Induced Flavor
- Caused by exposure of milk to sunlight or fluorescent light
- Actually light in the range of 350 to 500 nm will initiate the reaction
- In addition to a flavor issue, this reaction also results in a loss of nutrient (vitamin C and riboflavin)
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Prevention of Light-Induced Flavor
Avoid exposure to light
-Turn lights off in the dairy case
-Shield the light sources to avoid transmitting certain wavelengths
Use containers that do not transmit light
-Heavy, dark paperboard,
-Pigmented plastic
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Ultra High Temperature Processing (UHT)
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Production of sterile product
-With aseptic packaging
Production of ESL products
-With “typical” packaging
-Two major methods
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Range from 135-150°C for a few seconds
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Indirect Systems
Tubular
Plate
Scraped surface
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Direct Systems
In direct heatign systems, the fluid to be heated is in “intimate contact” with the heating medium. For example milk and steam are mixed together. Note that the water added by the steam must be removed. This is done using a flash cooling operation.
Direct heating systems are used in the UHT processing of milk. The major reason for using direct heating systems is that the rate of heating is much much greater than in indirect methods. Since heating is so much faster, the product is in the “product damage zone” for a much shorter period of time. This is illustrated on the next slide
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Direct & indirect Continuous Sterilization
As you can see from this chart, product which are heated indirectly are in the product damage zone for a significantly longer time than those that are heated directly.
This is a reslt of slower rates of both heating and cooling. Heating and cooling to the actual process temperature are esentially instantaneous in directly heated and flash cooled s
sytems.
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This is a cartoon of a direct steam injection processing system used for the processing of milk.
Milk flows from the Balance Tank (1a) through the plate heat exchanger (3) where it is preheated. It exits the plate heat exchanger and is pumped to the steam injector (5) where steam is mixed with the milk. The heated milk enter the hold tube (6) and then flows into the expansion chamber (7) were it is cooled by flash evaporation and then flows to an aseptic homogenizer (10) through the plate heat exchanger where it gives up heat to the process water
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Chemical Changes in Due to Heat Treatment
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Nutritional
-Vitamins
-Proteins
-Lactose
-Minerals
Structural and Quality
-Proteins
-Lipids
-Browning
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