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