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Enzymes
- Catalyze chemical reactions (look at chart)
- Enzymes convert foods in to less complex compounds
- Proteins, fats and carbohydrates are broken down to less complex compounds by enzymes
- Enzymes responsible for changes in flavor, color, texture and nutritional properties
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Enzyme Temperature
▫60-150°F optimal activity▫160-200°F inactivated
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Enzyme pH
- ▫Most enzymes active only over a narrow range
- ▫Optimum varies
- ▫Affects both catalytic activity and enzyme stability
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Proteolytic Enzymes
- Protease
- All enzymes that hydrolyze peptide bonds
- Bromelin (pineapple juice), Papain (papaya)
- Meat tenderizing, cheese manufacturing, textural modification
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Oxidizing Enzymes
- Oxidases
- Oxidation – loss of an electron by an atom or chemical combination with oxygen
- Many oxidizing enzymes in foods
- Oxidizing enzymes do not cause deterioration in intact tissues
- Polyphenoloxidase:Reacts with phenolic compounds
- -Responsible for browning in fruits and vegetables
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Ascorbic acid oxidase
- Oxidizing Enzymes - Oxidases
- Oxidizes vitamin C, resulting product not utilized by humans
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Tyrosinase
- Oxidizing Enzymes - Oxidases
- Oxidizes compounds related to tyrosineCauses black spot (lobsters, shrimp)
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Fat-Splitting Enzymes
- Lipases
- Breaks fat into glycerin and fatty acids
- ▫Large chain fatty acids (>10) smoking during heating
- ▫Short chain fatty acids – odor and flavor
- ▫▫Off flavors, rancid, unclean, bitter, soapy, cowy, butyric
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Enzymes that Breakdown Carbohydrates
- Carbohydrases
- Pectinase
- Catalyze the degradation of pectin (structure)
- Solids tend to settle to the bottom in fruit juices
- Produces softening of fruits
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Enzyme Applications-Proteases
- Used to chill-proof beer
- ▫Removes proteins that can cause clouding
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Enzyme Applications - Lipases
Breakdown fat Then enzymes produced by mold oxidize fatty acids that produce flavor
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Enzymen Applications - Invertase
Cherries rolled in sucrose and enzyme before they are covered in chocolate
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Heat treatment in the industry
- Pasteurization
- Blanching
- Baking
- Canning (commercial sterility)
- Extrusion cooking
- Microwave cooking
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What is heat?
- In physics:Transfer of energy from, one part of a substance to another because of a difference in temperature
- Heat is energy in transit
- It flows from higher temperature to lower
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Heat transfer
3 Processes
- Manner in which heat is transferred from a heat source to food particles in a container (can, bottle, pouch, etc)
- Destroys microorganisms in processed foods
- Three heat transfer processes
- -Conduction
- -Convection
- -Radiant Energy
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Degrees of preservation
Sterilization
- Complete destruction of Microorganisms
- Requires at least 250°F (121°C)
- Destruction of spores
- Time is important
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Degrees of preservation
Commercial Sterilization
- All pathogenic and toxin-forming organisms are destroyed
- May contain viable spores that can not grow under normal condition
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Pasteurization
- Low energy thermal processing (80 – 90 °C, 176 – 194 °F)
- Destroys all pathogenic microorganisms in specific products
- Extending the shelf life by lowering the number of spoilage organisms.
- Not a sterile product and subject to spoilage
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Blanching
- Mild heat treatment
- Used in fruits and vegetables
- To inactivate enzymes
- May destroy some microorganisms
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High heat
- Destroy all microbes
- Inactivate enzymes
- Effects on food quality
- Color
- Flavor
- Texture
- Nutritional value
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Selecting Heat Treatment
- 1.Time-temperature combination required to inactivate the most resistance microbes
- 2.Heat penetration characteristics of the food and container–Particle size–Consistency–Size, shape, material of the container
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Thermal Processing for Food Preservation
- Delay food perishability and inhibit food spoilage
- Targets both spoilage and pathogenic organisms
- SEEKS SPORE DESTRUCTION!!!!!!
- Microbial Death: Failure of cells to grow and reproduce
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Heat Treatment
- Time and temperature treatments vary among organisms
- Heating times and temperatures are based on the destruction of Clostridium botulinum spores
- -Toxins cause sickness and death
- -Most powerful toxin known
- The organism Bacillus stearothermophilus is used in laboratory trials to determine safe heat process
- -More heat-resistant then C. botulinum
- -This one is more heat resistant so if it is killed then C. Botulinum will be killed
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D-VALUE
- Time required at a certain temperature to kill 90% of the organisms being studied
- Offer the basis for calculating process times in the food industry
- D-value = 2.5 minutes at 250 °F (121°C)
- 1,000,000 (10^6)--->100,000 (10^5)-->10,000 (10^4)
- Each 90% reductions is a “log cycle”
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Heat Treatment
- Time of heating is determined by how many “log cycles” one wishes to reduce the population of bacteria
- Accepted heating time for canning is equal to the time required to decrease the bacterial population by 12 D-values
- Should destroy all pathogens and commercially sterilize the food
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Estimating Processing Times
- Need to take into account size, shape, and material the container is made from
- Need to determine length of time it takes to reach that temperature at the coolest point in the can
- Heating patterns differ with different foods
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Conduction
- Heat transferred between food molecules via molecular collisions
- Transfer occurs due to temperature gradients
- Relatively slow since it relies on direct contact
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Convection
- Heat is transferred through a liquid or gas
- Occurs due to density differences
- More effective than conduction
- Requires less time
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Radiation
- Transfer of energy in the form of electromagnetic waves
- Fastest method of heat transfer
- Transfers heat directly from the radiant heat source (broiler plate) to the food
- The contact surface between the heat source and food reduces the amount of heat
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Processing Times
- Determine the D-value
- Determine time needed for the coldest point to reach the required temperature
- Add that time to a time equivalent to 12 times the D-value
- Ensures reduction of 12 D-values and essentially sterilizes the food
- D-value = 2.78 minutes at 250 °F (121 °C)
- Takes 25 minutes to heat cold point of a canned food to 250 °F
- Processing time:25 + (2.78 x 12) = 58.36 minutes at 250 °F (121 °C)
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Still Retort Canning
- Convection heating through steam
- Conduction heating through hot walls of container
- stemm in a better heater. Air will take too long
- Product placed on a container and heated in a steam environment without agitation
- Cans are placed inside retort chamber and steam is injected under pressure
- Steam transfers heat into each can placed inside the retort
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Agitating Retort Canning
- Shaking to get better heat transfer. Same results but less time
- Cans enter the retort continuously
- Cans are conveyed back and forth as necessary and rotate around their long axisAgitation occurs speeding up heat penetration and shortening processing times
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Hydrostatic Retort
- System is partially filled with water
- Steam forces water up to higher levels in the entrance and exit chambers
- Cans enter continuously
- An agitating system
- Achieves commercial sterility
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Retort Canning Objectives
- Main objective to retort is subjecting cans to heat to kill the microorganisms
- Have to use clean potable water (water is not sterile)
- All cans have gone through some sort of heat processing
- When sealing can-want to create an environment with no oxygen
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Cooling Heat-Processed Foods
- Cooled in the retort by allowing water to flow after steam shut off
- Cans may be taken out and moved through a cooling canal
- Cooling water should be POTABLE!!!!!!
- Microscopic amount of cooling water may enter the cans
- High microbial counts in the water can lead to spoilage of the product
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The thermal preservation of foods Canning
Development of the metal cans include
- Various lacquers and lamination developed for lining
- Quick-open cans with pull tabs
- Cans which open with a slotted key
- Pressurized cans for whipped cream
- Plastic cans
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A typical canning process include:
- 1- Pretreatment of product:
- -clean, cut, pit, slice, dice, inspect, Etc
- 2- Blanching of product:
- -steam or hot water
- 3- Filling and creation of can vacuum:
- -The creation of vacuum removes oxygen from the can headspace minimizes swelling of the can due to pressure changes prevents collapsing (buckling) of the can during processing
- 4- sealing the cansa hermetic seal is formedenvironment inside the can is anaerobic
- 5- Processing the cans
- -in a retort process at 250F at 15 psi steam for up to two hours
- 6- Cool the cans in potable water!!!!!!!!
- 7- Pack cans in cases
- -Want temperature to remain between 50° to 85°F
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Foods are packed under vacuum for several reasons
- 1- To minimize swelling due to pressure changes
- 2- To remove oxygen from headspace
- 3- To prevent buckling during retort process
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How is a vacuum obtained in canned foods?
- 1.Add hot food to the container and seal
- 2.Pull a vacuum mechanically. Limitations
- 3.Steam jet vacuum. It is called “steam flow” vacuum
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Other Thermal Processing Method:
Aseptic Fill Method
- Employed following HTST
- Pureed material or liquid is passed through a heating system
- Product is pumped to a holding chamber where it is held at high T for 15-20 s
- Pumped through a cooling system (cooled quickly)
- Pumped to a filling system and forced into presterilized containers
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Other Thermal Processing method:
The Sous-Vide Process
- Means under vacuum
- Food is packaged under vacuum and heat processed Held refrigerated until used
- Problem: Process doesn’t kill Clostridium botulinum bacteria
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Other Thermal Processing method:
Modified-Atmosphere and Controlled Atmosphere Packaging (MAP):
- Removal of oxygen from the package and replacing it with more inert gas, e.g. Nitrogen
- This may enhance the growth of anaerobes so extreme care must be taken in handling and storing the foods ( < 40° F )
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Other Thermal Processing Method:
Microwave Processing
- This energy form, applied at either 915 or 2450 megahertz, is used for baking, pasteurization, and sterilization
- Because the highest temp. in microwave is 212° F, in order to obtain higher temperatures, the chamber must be pressurized
- Now is used for blanching, puffing, and concentrates
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Dehydration
- Removal of water to extend shelf-life and reduce storage and transportation costs
- Implies removing almost all the water from solid and liquid foods to as low as 5% moisture content
- Dehydration is a heat and mass transfer process
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Heat and Mass transfer of Dehydration
- Heat transfer into the food to provide the latent heat of evaporation
- Mass transfer of the water out of the food
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Sun Drying
- Attractive in terms of zero energy cost
- In direct sunlight or shaded areas
- Produced in areas where climate provides high temperatures and low humidity
- Disadvantages include slow drying rates, difficulty achieving low moisture content and risk of contamination
- Peaches, Tomatoes, Coffee, Raisins, Black pepper, Chili
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Hot air drying
- Heated air is circulated Temperature, relative humidity, and air velocity are controlled
- Water is picked up from the surface and carried away
- Time required for drying depends on the characteristics of the raw material
- Initially evaporation of moisture from the food surface takes place
- Diffusion of water, water vapor, or both, to the surface of the food
- Dryers often have multi-zone design where air flow pattern, temperature, and speed vary
- Air flow can be co-current or counter-current to the food
- Counter-current allows for lower final moisture content
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Hot air drying
Cabinet dryers
- A small batch convection dryer used for fruit and vegetables
- Food is placed on screen mesh trays and hot air passes across the food and is then exhausted or circulated
- Hot air is circulated by blowers or fans of different designs
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Hot air drying
Tunnel Carts/Belt Dryers
- Many designs fit under this category
- Continuous dryers are industry standard
- They are designed as elongated cabinets where food moves through them on belts or on trays stacked on carts
- Residence time is controlled by the belt or cart speed
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Effect on Food
- Foods undergo breakdown and loss of quality due to heating
- Important to control time and temperature
- Recommended to use higher temperatures at beginning of the drying cycle
- Amount of surface water is highest
- Heating is countered by evaporation of the surface water
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Fluidized-Bed Dryers
- The objective is to increase the rate of heat transfer
- Air is blown through the bottom of porous plate at high enough velocity to fluidize the food pieces into gentle boiling motion
- Products: Peas, grains, vegetables (diced)
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Drum Dryers
- Products flow onto the surface of two heated stainless steel drums
- Drums rotate in opposite directions
- Product is dried on the drums and scraped off by stationary blades
- Yield low quality products because of thermal degradation
- Used for dry thick products
- The food is applied as a thin layer onto the surface of a revolving single or double drums
- Steam is used to heat the drum from within
- The dry food is then scraped from the surface by a doctor blade
- Drum drying is mostly used for potatoes, oatmeal and animal feed
- Using drum drying under vacuum minimizes thermal degradation
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Freeze Drying
- Freezing the food and sublimating the waterFood is freezed
- Vacuum is applied and temperature raised
- Moisture sublimates
- NO MELTING!!!!!!!!
- Produce very high quality products
- Utilized for heat sensitive, high quality foods
- Freezing the food separates the water as ice crystals
- Temperatures range from 100 to 180 F
- Vacuum and hot plates cause ice sublimation to vapor
- Vapor is removed via refrigeration unit
- Freeze dried foods have sponge-like texture, maintain their original shape, and are easy to hydrate
- Moisture content as low as 3%
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Spray Dryers
- Used for drying liquid foods
- In the dryer, the liquid is converted into fine mist by the atomizer which can be high pressure nozzle or spinning disc
- The fine mist contacts the hot air and turns into powder instantaneously
- Particles are collected with the aid of scrapers
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Reconstitution
- Dried foods must be reconstituted (add water)
- Changes in food affect the rate and extent to which water will be taken up
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Drying Packaging
- Minimal specifications (cereals, vegetables)
- Packaged to prevent moisture from entering the product (fruit juices)
- If low moisture content is lost non-enzymatic browning can result
- Fats are exposed to oxygen --->off-flavor (oxidation)
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Drying - Microorganisms
- Point of drying is to reduce moisture content to keep microorganisms from growing
- Growth depends on water activity
- Drying will not kill microorganisms!!!!!!!
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Spoilage of Dried Foods
- Oxidation of fats
- ▫Jerky, fish, shrimp
- ▫Vacuum pack, inert gas
- ▫Addition of antioxidants (limitations)
- Enzymatic & Nonenzymatic browning
- ▫Keep moisture content below 2%
- ▫Blanching (Enzymatic)
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Refrigeration
- Gentle method of food preservation
- Carried out at temperatures above freezing
- About 85% of foods are refrigerated
- Mechanical refrigeration was developed to produce ice
- Extends shelf-life of foods
- Create few adverse effects
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Refrigerator parts
- Compressor
- Evaporator
- Condenser
- Expansion Valve
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Early Refridgerators
- Ice boxes: ice was placed in a chamber at the top in order to cool a lower chamber
- Very little was known about the theory of refrigeration
- Research was required to develop effective refrigeration systems
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Other Refrigerator methods
- Chilled Seawater (CSW)
- -Mixing seawater and ice
- -Place fish in mixture
- Refrigerated Seawater (RSW)
- -Mechanically refrigerated water
- -Place fish in the mixture
- Achieve more uniform cooling than ice alone
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Quick Freezing
- Dates back to Eskimos and Native Americans (freezing)
- Quick freezing began around early 1900s
- A fall from 32 to 25 F in under 30 minutes
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Preservation Effect of Freezing
- Microbial and chemical spoilage of foods occurs due to high water activity (aw)
- During freezing the aw is lowered to levels that prevent functioning of microbes
- The aw is lowered to levels that reduce the rates of chemical reactions
- Slowly
- -Water molecules migrate to ice crystals
- -Large ice crystals are formed
- Fast
- -No time for water to migrate to ice crystals
- -Small ice crystals are formed
- -Small ice crystals are more desirable
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Benefits of freezing
- Extends shelf-life
- Preserves food without major changes in size, shape, color, texture and flavor
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Air Blast freezing
- Most commonly used procedure for freezing foods
- Food is packaged and placed on racks
- Racks are wheeled into tunnels
- Air is blown over the product at -20 to -40 F
- When product T reaches 0F the packages are stored at 0F or below
- Also applied to products on a belt
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Plate Freezing
- Layers of packaged product are sandwiched between metal plates
- Refrigerant flows through the plates at -28 F
- Full contact is made with the product
- Temperature is brought to 0F within 1.5 to 4 hours
- Used for meat, fish, and dairy
- Continuous operation plate freezers are used in commercial plate freezing
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Liquid Freezers
- Liquids such as nitrogen and dry ice (CO2) may be used for quick freezing
- Liquid Nitrogen = - 320 F
- CO2 = -110.2 in solid state
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Liquid Nitrogen
- Food portion is placed on a moving stainless steel belt
- Sprayed with liquid nitrogen
- Food leaves freezer in a frozen state and is packaged, cased, and stored
- Very used for marine products (Shrimp)
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Dry Ice CO2
- Powdered CO2 is mixed with the food
- Liquid CO2 under pressure is sprayed onto the food surface
- Food is quickly frozen
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Why is food quality is better when frozen quickly:
- 1.Rapid freezing results in small crystal formation (less damage to the product)
- 2.Rates of chemical and biochemical changes are reduced
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Freezing and Microorganisms
- Freezing will not kill MOs
- When frozen food is thawed, MOs growth will resume
- Frozen food may become a health risk if improperly prepared
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Frozen Product Quality
- Frozen food preparation
- -▫Blanching, concentration
- Packaging
- -▫Moisture-vapor-proof
- Physical, chemical, and enzymatic
- -▫Moisture loss, oxidation, protein denaturation, enzyme reactions
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Thawing
- An undesirable aspect of freezing preservation
- Time consuming
- Associated with loss of product quality
- Accepted thawing practices
- Under refrigeration below 40F
- Under running water below 70 FAs part of the cooking process
- Bulk food are problematic
- Bulk foods take long to defrost
- Defrost rate is dependent on temperature
- Tendency to defrost at high T
- Outside portion of the food is subject to bacterial decomposition and yeast growth
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Breakdown of milk
- 88% Water
- 3.3% Protein
- 3.3% Fat
- 4.7% Carbohydrate
- 0.7% Ash
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What two bacterias are herds tested for
Herds are tested for tuberculosis and brucellosis
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Sources of Bacteria in Milk
- Normally present in the udder
- Body of the cow
- Milking machines
- Equipment Hands, nose, and throat of dairy workers
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Precautions taken when milking
- Udders should be washed, sanitized and dried
- Milking machines are cleaned and disinfected with live steam or with chlorine solution (200ppm)
- Milk tanks are cleaned with detergent and water at 130 F, and then sanitized with chlorine
- Water supplies used must be potable
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Improper handling of milk
- Improper Cooling
- -Microorganism growth
- Inadequate Cow Feed (wild onions, french weed, potatoes, cabbage, turnips)
- -Off-flavors
- Oxidation
- -Off-flavors
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When milk is picked up at the dairy
- Tested for odor and flavor
- -Accepted or Rejected
- Butterfat content measured
- -Farmer paid on basis of butterfat content
- Tested for Antibiotics
- -Severe penalties
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Processing of fluid milk
- 1.Clarification
- 2.Adjust Butterfat Content
- 3.Fortify with Vitamin D
- 4.Pasteurize
- 5.Enhance Flavor
- 6.Cool
- 7.Pour into containers
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Adjust Fat Content
- Fat content standardized
- Adding cream or skim milk
- Provide fat content determined by state regulations
- Fortified with Vitamin D
- One serving (8 oz) contains 10 mg (25% DV)
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Pasteurization
- Destroys organisms known to represent a health concern
- Extend the shelf life of the milk
- “Vat Method” : 145°F for 30 min
- HTST, 161°F for 15 sec,
- 191°F for 1 sec or 194°F 0.5 sec
- Then Cooled
- Ensure destruction of Coxiella burnetti
- -Responsible for Q fever
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Flavor Treatment
- Heated to 195 °F and subjected to vacuum
- VacuumRegulates flavor
- -Cools the milk
- -Evaporate any residual water
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Homogenization
- Break up fat globules to small size
- Prevents cream separation from milk
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Skim Milk Low Fat Milk
- Produced from whole milk
- Milk is passed through a centrifuge at high speeds after heating to 90 – 100 °F
- Butterfat is removed as cream
- Fortified with vitamin D and A!!!!!!!!!
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Types of Ice Cream
- Standard – cream, milk, sugar
- French (custard) – have egg yolks added to improve texture
- Gelato – high butterfat, egg yolks
- Reduced-fat, low-fat, nonfat – progressively less fat, use additives to maintain texture
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Yogurt
- Results from growth of microorganisms
- -Lactobacillus bulgaricus
- -Streptococcus thermophilus
- Bacteria may be naturally present in milk
- Added as cultures to ensure consistent quality
- Other ingredients
- -Skim milk, condensed milk, nonfat dry milk, modified starches, low-fat products
- Mixes are blended, homogenized, and pasteurized
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Yogurt making process
- Pasteurized 190.4°F for 30 minutes
- Cooled to incubation temperature (113 °F)
- Liquid cultures are added
- Mixture is filled into containers that may contain fruit
- Incubated until a pH of 4.4 is attained
- Cooled and held at 39.2 °F
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Milk quality problems
- Whey Separation
- -Uneven incubation temperatures
- -Insufficient cooling
- Too much acidity
- -Improper fermentation conditions
- -Contaminated cultures
- Off-Flavors
- -Improperly handled milk
- -Thermophilic bacteira and yeasts
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Cereal Grain importance
- Plants that produce cereal grains are the most important for the diet
- Grown in a variety of regions
- Produce high yields per acre
- Excellent storage stability
- High nutritional value
-
Grain anatonmy
- Bran: Protective outer coat
- Germ: Embryo
- Endosperm: Contains starch and proteins
- Endosperm (starchy, rich in protein)
- Hull/bran (protective layer, indigestible, rich in B vitamins and minerals)
- Germ/embryo (high in oil, enzymatically active)
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Cereal Grains nutrition
- Most grains contain the essential amino acids required by humans
- Exception: Lysine and Tryptophan
- 11% Protein
- 3% Fat
- 12% Moisture
- 68% Carbohydrate
- Fiber 6%
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Top produced cereal grain
- Corn is produced the most
- -majority of it is for livestock feed
- Wheat is the most produced for human consumption
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Processed Cereal grains
- Bran and germ are removed
- -Bran: Indigestible to humans
- -Germ: High oil content
- Germ is used for oil production
- More bran is being used
- -Higher fiber diets
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Wheat
- Wheat proteins produce doughs of proper strength and elasticity
- Provides desired texture and flavor
- Cut the stalk
- Remove and collect the seed
- Stored
- Cleaned and prepared for milling
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Wheat Milling
- Grinding of the grain into a form easily incorporated into foods or cooked
- Process can be dry or wet
- -Wheat is dry-milled
- Separation of the endosperm from bran
- Different flours are produced
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Many varieties of cornSweet cornCanned or frozenPopcornLower in protein content than wheatHarvested by combine and wet-milling
- Many varieties of corn
- -Sweet corn
- -Canned or frozen
- -Popcorn
- Lower in protein content than wheat
- Harvested by combine and wet-milling
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Milling Corn
- Moistened to 21% water content
- Germ removed mechanically
- Endosperm is dried to 15% moisture content
- Passed through crushing rolls and bran is removed
- Separated using sieves (grits, flours)
-
Barley
- Barley products don’t bake well
- Has little or no gluten
- Grows in cold climates
- Grows in soils too poor to support wheat
- Used as feed for cattle
- Ingredient in soups
- Mainly used for producing malt
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Malt
- Grains are soaked in water
- Moisture content 50%Sprouting
- Dried with air at 65 to 70 °F
- Produces enzymes that will break down the starch
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