Lecture 3 Flashcards
What is the chilling storage temp range?
<15C to >0C
What are commercial values of chilling?
4.4-7C
What does chilling do?
Slows:
Growth of Micro-organisms except Psychrophile
Metabolic Activity of plant and animal tissues
Chemical Rxn: Enzyme Catalyzed Oxidation
Moisture Loss
-dont become wilted
What is a controlled/modified atmosphere?
Decrease O2 to 3-5% and Increase CO2 to 3-5%
Modified Atmosphere slow down Aerobic Respiration
Decrease this by decrease O2 or temp
lower rate of respiration lower spoilage
What is the composition of air?
Air is composed of 78% N and 21% O2
In chilling storage, do we want to remove all the O2?
No, because that would result in anaerobic respiration which may produce toxins and alcohol.
What does chilling storage promote?
Cold Shortening of Animal Muscle (Meat toughness)
-Muscle are contracted=toughness
Chilling Injury of Fruit/Vegetables (Apple softness)
Chill Sweetening in Potatoes
-Accumualtion of sugars in potatoes and result in access browning when you fry the potatoes
Staling of Bread
- Bread firmness due to Retrogradation
- (Re-arrangement of Amylose and Amylopection)
What is happening to leftovers in the refrigerator?
1) Slow microbial growth
2) Enzymatic changes that may cause off-flavour
What do you think are the most important factors
1) Refrigerate foods ASAP
2) Pack foods in small portions
3) Avoid cross contamination
Fruits and vegetables coming into storage are usually contaminated, especially with mold spores, sure or false?
True
What kind of deterioration are the enzymes Lipoxygenases Lipases Proteases Responsible for?
Off-Flavour
(Rancidity)
• Affect protein, and can breakdown protein and lipid structure
What kind of deterioration are the enzymes
Pectic Enzymes
Cellulase
Responsible for?
Off-Texture
Excess Tissue Softening
• Affect cellulos and pectin,
What kind of deterioration are the enzymes Polyphenol Oxidase Chlorophyllase Peroxidase Responsible for?
OFF-Colour
Discolouration
What kind of deterioration are the enzymes
Ascorbic Acid Oxidase
Thiaminase
Responsible for?
Nutrient Loss
What are the optimal temperatures for chilled storage of meat and dairy?
Fresh Meat and Fish
1 to 1C
Dairy 0.5C
Cooked Meats and Fruits 2 to 8C
Typical Home Refrigerator
4 to 8C
What are the other factors that affect shelf-life?
Light
Pasteurization
Waxing or Oiling
Controlled Atmosphere
Why does light affect shelf life?
Promote Sprouting of Potatoes, Onions
Store in dark dry and cold environment to inhibit sprouting
Why does pasteurization affect shelf life?
Pseudomonas fluorescens????
- Spoilage bacteria
- HEAT Resistant, not destroyed by pasteurization
Spoilage bacteria that casues slimelyness in dairy, is heat resistant (not destroyed by pasteurization
Why does waxing or oiling affect shelf life?
Decrease Dehydration: Fruits/Vegetables
Decrease Dehydration and CO2 losses : Eggs
-CO2 when inside of the egg regulates the pH, whe Co2 is lost pH increases and the whites make it more runny
Why does a controlled atmosphere affect shelf life?
Decrease Aerobic Respiration
-Decreasing rate of spoilage
Decrease M.O. Growth
-Especially those that are aerobic
Decrease Oxidation
-Less rancidity
What are the temperatures for freezing?
Freezing: Optimum Temperature for Home Freezing: -18oC
What is crystallization?
The formation of systematically organized solid phase from solution
What does freezing consist of?
1) Nucleation: Site for Crystal Growth (Seed Formation is association of molecules into tiny ordered particles)
2) Crystal Growth: Enlargement of Nucleus
What does freezing do?
Decreases Water Activity (aw)
Reduce Microbial Activity
Reduce Rate of Chemical Reactions
(i.e., Lipid Oxidation)
Less free water thee less activity and can result in less microorganism activity
What are the 2 kinds of ice crystal formation?
Slow and fast freezing
What us the difference between the 2 kinds of ice crystal formation?
Slow Freezing (H2O molecules have enough time to migrate to seed crystals)
- Large Ice Crystals
- Not Desirable
- Home freezer
- Result in few large crystals, hase more time to igrate to other seed crystals
Fast Freezing known as Cryogenic Freezing
- Small Ice Crystal
- Desirable
If freezing stops growth of bacteria, why does frozen foods have a best before date?
1) Quality
2) Sensory Properties
- Enzymes are stiill active
Freeze Concentration can increase the concentration of enzymes and their substrates and result in faster reaction rates, true or false?
True
What are the advantages of rapid freezing?
Formation of a large number of small ice crystals that are evenly distributed
Less damage to tissue
Lower movement of soluble component within food b/c time of solidification is short
-Soluble component= sugars and salts
Reduction in rate of chemical Rxn.
What are the ways that quality of the product can deteriorate during freezing?
Drying Out: Freezer Burn (poor packaging)
-Still safe to eat just sensory qualities decrease
Lactose Crystallization> Sandiness of Ice Cream
-Whe there is a flux in temp when storage
Loss of Volatile Components
-Are lost during storage
Protein Denaturation > Toughness of Meat
Oxidation of Vitamin C, Thiamin, Riboflavin
Oxidation of Fat > Rancidity
Colour Change: Degradation of Chlorophyll
-Decrease green colour in vegetables
What is recrystallization?
Unstable Crystals> Metamorphic Changes
Change in #, Size, Shape
Change in Orientation
Is not desireable because sensroy properties are going to be damaged
What are the possible reasons for recrystallization?
Increased Temp. or Fluctuating Temp.
What is the freezing curve for Water?
A- S: Cooling- No : H20> Ice Transformation
S-B: Temp- Release Heat of Crystallization
-First ice crystals are formed at point B ith initial freezing point
B-C: Major Portion of H20 Crystallized
C: Eutectic Point: Solutes Freeze
C-D: More Crystallization
What is thawing, how should we do it?
Time Consuming
Loss of Quality: Enzymatic and Microbial Activities
Recommended Condition for Thawing is either Temp < 7.2oC or under Running Cold Water
Freeze Food in Small Packages >Thaw Faster
What is the thermal conductivity of ice?
Thermal Conductivity of Ice is 4 Times Greater than Water
Freezing:
- Ice Layer Expanding
- Ice Transmits Energy Rapidly
- Solid phase expanding in freezing
Thawing:
- H20 Layer Expands
- H20 is a Better Insulator
- Liquid layer is expanding and water is less thermo conductive
What are the different methods of freezing?
Air blast freezing (most common)
Plate freezing
Liquid Freezer
Slow freezing
What is air blast freezing?
Some foods are packaged first Placed on racks Send into insulated tunnel (-30oC, -40oC) Cold Air is blown over them (500-1500 ft/min) Peas are frozen first-> then Packaged -(will result in 5% moisture loss)
What is plate freezing
-Foods are packaged
Sandwiched between metal plates (Full contact with the products)
Temperature: -34C
What is liquid freezer?
Liquid Nitrogen: Flash Freezing
Liquid CO2: Quick Freeze
Cryogenic liquids are liquefied gases of extremely low boiling point (b.p.)
High quality frozen product
Individual food portion is sprayed with liquid N2
What temp does liquid CO2 and N2 boil at?
CO2: -79C
N2: -196C
What are the advantages of liquid N2?
B.P. = -196oC
(Great driving force for heat transfer)
Intimate Contact (Irregular shaped foods)
Nontoxic and Inert
Replaced 02, Lower oxidation
Fast: High Quality
What are the disadvantages of liquid N2?
high cost
Some safety issues
The speed of liquid-nitrogen freezing produces frozen foods with a quality unattainable by non-cryogenic freezing methods true or false?
True
In Cryogenic liquids, cold temperature results from______ of liquid nitrogen or CO2.?
Evapration
Some products such as mushrooms cannot be frozen by other methods without excessive tissue damage, true or false?
True
What is slow freezing?
Fruits, Fish
Cold Room: -23oC, to -34oC with some air circulation
Glaze Formation (Coating of ice prevents dehydration) -Dip fish in water than put in freezer to have a thin layer of ice in fish to prevent dehydration
Why is blanching used as a pre treatment method for freezing?
Mild heat process To inactivate enzymes (Catalase and Peroxidase)
-Indicator enzymes for blanching
To destroy some microorganisms
To fix colour of green vegetables
What temp should you keep frozen things at?
-18C or lower
Why is -18C for frozen things too strict?
- Food pathogens do not grow below 3.3oC
- Food spoilage does not happen below -9.5oC
What is the reason for choosing -18oC for freezing?
Enzymes are very resistant to cold temperature and may stay active at even -18oC.
What are the factors of determining the freezing rate?
1) Driving Force
- The temperature difference between the product and the cooling medium
2) Resistance to heat transfer, which depends on:
- Air velocity
- Thickness of product
- Composition of the product
What is the order of chemical comp and thermal conductivity?
Air
What are the 3 stages of deterioration changes?
Freezing
Frozen
Thawing
What impact does freezing have on microorganisms?
Microbial Changes: Few Will Die, Many Survive
Physical Changes: Ice Crystals Rupture Cells
Chemical Changes: Freeze Concentration
What impact does frozen storage have on microorganisms?
Microbial: M.O. Survive but most Do Not Grow
Physical: Colour Changes, Re-Crystallization, Dehydration
Chemical: Enzymatic RXN (Lipoxygenase) and Oxidation of Vit. C
What impact does thawing have on microorganisms?
Microbial
Some Growth
Physical
Ice Crystals Start to Melt (Solid Liquid)
Chemical
Enzymatic RXN.
Why are packaging materials important?
The resistance to heat transfer of the food package depends on:
The more direct contact between food and cold medium > Higher Freezing Rate
What makes a good packaging for freezing?
Resistant to the permeation of water vapour to inhibit dehydration
Strong and Flexible
Protective against light and air
Liquid-tight to prevent leaking on thawing
What are some packaging materials?
Plastic bags
Aluminum foil wraps
Plastic wrap
Waxed paper
**Glass is not recommended due to breakage from expansion during freezing
Freezing and frozen transportation and storage are highly energy intensive and ______?
Costly
What are other methods of processing that may yield products equal or nearly equal in quality to those obtained by freezing?
Concentration followed by freezing (Orange Juice).
High Temp. Short Time (HTST) followed by aseptic packaging
Irradiation
What is concentration?
The removal of H20
Advantages: Easier Transport and Storage
What is evaporation?
Heating liquid to the Boiling Point to remove H20 as vapour
What are the different ways you can concentrate something?
Evaporation
Vacuum Evaporation
Reverse Osmosis (RO):
Partial Freezing and Removal of Ice Crystals
What is reverse osmosis?
Applying a mechanical force which exceeds the osmotic pressure, H20 moves in reverse direction
By applying a mechanical force which exceeds the osmotic pressure, H20 moves in
reverse direction
What is the purpose of evaporation?
Volume reduction (juices, cheese whey)
Preparation of conc. foods (syrup, sauces)
Preparation of dehydrated foods
Preservation (intermediate H20: 20-50%)
How can you concentrate heat sensitive liquids?
Evaporate under vacuum (Lower Temp.)
-Don’t have to heat it as much
Membrane Separation (M.S.) -To remove excess water
What is the membrane separation process?
The principal Membrane Separation processes; in order of pore size:
-Separate Particles based on size as follows:
µF UF RO
0.1-10µ .01-0.1µ 0.001µ
Micro, ultra filtration and reverse osmosis
What are the advantages of membrane separation?
Same equipment can be used for different processes and purposes
What is the difference between Micro, ultra filtration and reverse osmosis ?
RO only lets water filter through
Ultra lets water and sugars and low molecular weight compounds
Why is reverse osmosis used?
useful in small scale operations
As a substitute for evaporation
-NOT suitable for some products
Pre-Concentration before evaporation
-More energy efficient
What products can be made with reverse osmosis?
Juice Concentration
Concentration of Grape Juice: Wine Making
Cheese whey Concentration
Desalination of Sea Water
Why is ultra filtrate used?
*Concentration of proteins in cheese whey
Clarification of wine
Why is microiltrate used?
Permeable to all solutes, but not to colloidal materials or particles such as Precipitated Protein & Pectic Substances
Clarification of juices and wines
-Remove suspended particles & Precipitated Proteins
What products are used in micro filtration?
Cold Pasteurization of Beer (Draft Beer in bottles)
-Remove Microorganisms
Remove Spore Forming Bacteria that produce gas during ripening of cheese
-(Dutch and Swiss style cheeses)
