Lecture 5: Food storage Flashcards
What is the most common form of food preservation?
Cold temperature food preservation.
What are the two main ways someone uses cold storage of foods?
- Refrigeration
- Freezing
What dose low temperature actually do?
The use of low temperature can extend the shelf life of food.
What is “Refrigeration”
anything from 0 to 5 C
What is “Freezing”
anything from 0 to -18C
When was the first mechanical ammonia based refrigeration system invented?
in 1875
How dose a refrigerator work?
You have a box with a contained system that has a Refrigerant within it.
What is a refrigerant?
Liquid that evaporates inside the refrigerator to create cold temperatures
What are the two things that you need to know about chemistry to understand refrigerators?
When liquid evaporates it absorbs heat
When vapor condenses it releases heat.
What is one of the most common refrigerants?
Hydrofluorocarbons (HFCs)
What is the goal of food preservation?
- minimize food spoilage
- Maximize safety and stability
- Maintain nutritional value and acceptability
- goals may be short or long term.
What is the purpose of Refrigeration?
- A means of gently reducing the temperature of a food item to slow down food deterioration due to microbes, chemicals, and enzymes.
True or false:
Refrigeration is often combined with other
preservation methods
True
Why is ammonia bad as a refrigerant?
Super toxic.
What is the best way to predict the length of time a food product will last in a fridge?
Through looking at the temperature of the fridge
What is the temp of the average of the household fridge?
4.5-7C
PHF means what?
Potentially hazardous foods
What type of microbes may grow in the fridge?
Psychrophilic microbes
True or false:
Refrigeration destroys all microbes?
false:
Other microbes are not destroyed by refrigeration temperatures.
When dose refrigeration work best?
When foods are cooled right after slaughter/harvest.
What do we do to employ rapid heat removal?
Hydrocooling, vacuum cooling
Refrigerated storage requires control of T, air circulation, and ______
humidity
80% to 95%
What are the effects of refrigeration storage on foods?
- minimal effects on taste, texture, and nutritional value.
What are some adverse effects of refrigeration on foods?
- Chill injury to fruits
- Flavor/odour absorption
- Changes in firmness, color, and flavor
True or false:
Refrigeration is not a good preservation method for every food.
true
Why don’t we put potatoes in the fridge?
it absorbed proteins and undergoes the miard reaction (browning)
What technology has ushered in the age of convenience foods?
Freezing
Who is the father of frozen foods?
Clarence Birdseye (1920’s)
What is the growth rate of frozen fruits and vegetables?
Sales are growing at a rate of 4% per year.
Why are sales of frozen foods increasing so much?
- Increased consumption of plant-based foods
- Convenience
- New product offerings
- Suited for small households.
Dose freezing destroy microbes and enzymes?
No, although it will greatly reduce the rate of food deterioration.
What happens to microbes when they are frozen?
They decrease in activity due to water being unabaibile (in solid form)
What happens to enzymes when they are frozen?
They maintain level of activity, which is why it is important to blanch foods before freezing.
Is there a set shelf life within frozen foods?
It is dependent upon the temperature.
What is the average temp frozen food is stored at?
-18 C or around it.
What is freezing point depression?
reduces freezing point below 0C
What depresses freezing point?
Dissolved substances in the aqueous phase will depress the freezing point.
Method process analysis is
Macroscopic
What is most important when attempting to maintain quality within frozen foods?
A fast freeze
The faster the freeze, the smaller the crystals
How much more voluminous is ice than water
Water = x
ice = 1.09x
What is the benefit of small ice crystals?
it results in better quality products
Why are large ice crystals bad?
large ice crystals will damage the cell structure of fruits & vegetables and meats
What is the result of inconsistent freezing rate in foods?
Inconsistent size of ice crystals
What do you do when you want to maintain quality (texture) of froze foods.
Rapid freezing
How do you promote the production of small ice crystals
modify the food product to increase surface area of he food product.
What effect will large ice crystals have on foods?
- damage plant and animal cells
- Juice are released upon thawing
- loss of moisture, water, soluble nutrients, firmness
- poor quality products (soft texture)
What effect do fluctuating temperatures have on food quality?
- shorter shelf life
- thaw - refreezing cycle will make large crystals.
How will moisture loss change the texture of frozen foods?
Freezer burn may be caused.
What is freezer burn?
Frozen food damaged by dehydration and oxidation due to air reaching the foods surface.
How do you prevent freezer burn?
Moisture resistant, airtight packaging.
Why do vegetables need blanching prior to freezing?
Blanching inactivate enzymes in the vegetables. Helping to maintain original quality.
What are the effect of over blanching vegies?
Loss of color
What are the effects of under blanching vegies?
Stimulates enzyme activity
What is blanching?
Treating vegetables with steam or boiling water for a short period of time and then shocked with ice water to halt the cooking process.
What are the three main purposes of blanching vegetables?
- Denature (inactivate) naturally occurring enzymes to prevent spoilage.
- reduces microbial load (mild effect)
- aid in the removal of skins from nuts and fruits,
What is a flum?
A common method of moving things around.
When is blanching used?
before fruits/vegetables are frozen, caned, or dried.
What is one of the chemical changes of enzymes within foods when frozen.
They can cause browning
What Vitamin is lost in fruits when frozen?
Vit C is lost when frozen.
Are fruits blanched?
Not normally, this is in order to maintain freshness.
What is another method to control enzyme activity within frozen foods?
Use of chemical compounds can control enzyme activity
What are methods of preventing browning
Addition of ascorbic acid to reduce browning
What is it called when you try to make more money from your product?
Value added
What are some compounds used as a “Prevention” of browning of frozen foods?
Citric acid, lemon juice and sugar syrup used but not as effective.
What happens to fats when frozen?
They can undergo rancidity.
Undergoing oxidation of the fats, resulting in off-falvours and odors.
What food products are most likely to see fat based rancidity?
Foods with high fat content.
Fish and meats.
How do you prevent Fat rancidity when they are frozen?
Wrapping/packing material, vacuum packing them.
What are three results of unintentional freeze concentration?
- water would like to freeze as pure ice crystals
- water “moves” and leaves concentrated solutes behind.
- The solutes undergo deleterious reactions
What are some desired outcomes of freeze concentration.
An alternative to evaporation processes
used for aroma reduction for higher quality products (Fruit juice, coffee, extracts)
Freezing point decreases by 1.88 C for each increasing of how many moles of solute?
1 mole of solute decreases freezing temp by 1.885 C
What are the three main categories of industrial freezing techniques?
Air
Contact pate
Immersion
What are the three different types of freezing within the “Air” category?
Sharp freezing
Blast freezer
Liquidized bed freezer
What is still freezing?
Placing the product in still cold air, allowing them to freeze.
What is Blast freezing?
Pushing cold air at high velocity across a food product in order to freeze it as quickly as possible.
What is Batch Blast Freezing?
Food stacked on trays in rooms or cabinets to be frozen.
What is continuous blast freezing?
Product is frozen as it moves through a tunnel on a conveyer belt.
What is the primary goal of blast freezing?
Fast freezing.
What is a Fluidized bed freezer?
Refrigerated air is forced under a perforated tray and “products behave like liquid”
What are the benefits of a Fluidized bed freezer?
Superior product quality, through quick freeze and minimal dehydration.
What is the main use of Fluidized bed freezer?
Creates IQF food products for consumers and as ingredients in food industry formulations
What is the process of Contact plat freezers?
- After loading the food products, the plates are pressed
2. refrigerant circulates through plates, freezing the product by contact.
What is contact plat freezing used for?
Used for flat food products or “brick shaped packaged products’
Where is one place the contact plate freezer used?
on fishing trawlers.
What is the main freezing method around immersion?
Cryogenic freezing
What is cryogenic freezing?
Food is exposed to -60C through direct contact with liquefied gases (LN2, or CO2)
What foods are commonly frozen through cryogenic freezing?
High value products such as: Fish fillets Seafoods fruits Berries
What is an example of a cryogenic food product?
Dippin’Dots are a cryogenically frozen ice cream.
True or false:
Frozen foods can be more nutritious than fresh.
Sometimes true.
How long dose it take between harvest of vegetable and consumption?
generally 2 weeks, meaning there is 2 weeks of deterioration.
What is the % loss of nutrients in Green beans from harvest to plate?
45% (11-15 days from field to plate)
Why are frozen vegetables better for your than fresh?
Because they are processes (frozen) the same day they are picked. limiting the amount of nutrient loss
