Freezing and Concentrations
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What happens to leftovers in the refrigerator?
1) Slow microbial growth 2) Enzymatic changes that may cause off flavour
What do think are the most important factors for older adults to know about refrigeration?
1) Refrigerate foods ASAP 2) Pack foods in small portions 3) Avoid cross contamination
TRUE or FALSE? Fruits and vegetables coming into storage are usually contaminated, especially with mold spores
TRUE
If freezing stops growth of bacteria, why does frozen foods have a best before date?
1) Quality 2) Sensory properties
TRUE or FALSE? Freeze concentration can increase the concentration of enzymes and their substrates and result in faster reaction rates
TRUE
TRUE or FALSE? The speed of liquid nitrogen freezing produces frozen foods with a quality unattainable by non-cryogenic freezing methods
TRUE
In cryogenic liquids, cold temperature result from __________ of liquid nitrogen and CO2
Evaporation
TRUE or FALSE? Some products such as mushrooms cannot be frozen by other methods without excessive tissue damage
TRUE
What is the reason for choosing -18 degrees C for freezing?
Enzymes are very resistant to cold temperature and may stay active at even -18 degree C
What are other methods of processing that may yield products equal or nearly equal in quality to those obtained by freezing?
1) Concentration followed by freezing (orange juice) 2) High temperature short time (HTST) followed by ascetic packaging 3) Irradiation
Refrigerated or chilled foods are foods that are stored at temperatures below __________ and above __________
15 degrees C; 0 degrees C
Apple may become __________ if stored at too __________ a temperature, and bananas turn dark in the __________
Soft; cold; refrigerator
____________________ in potatoes is a phenomenon that causes potatoes to accumulate sugar (from the conversion of starch) during cold storage
Chill sweetening
Cold shortening in meats results in increased __________ when meat is cooled before rigor mortis progresses
Toughness
Saturated air has a relative humidity (RH) of __________. Hygroscopic products (e.g., nuts, dried fruits) must be stored at __________ RH
100%; low
Fruits and vegetables going into storage are usually contaminated, especially with __________ spores
Mold
Define pre-cooling of fruits/vegetables
Fast cooldown prior to storage or shipment to decrease temperature rapidly. (e.g., asparagus, snap peas, broccoli, beets, and other leafy vegetables are treated by top ice, ice slush, or cold water after harvest)
The objective of modified atmosphere storage is to ____________________ of fruits and vegetables
Decrease respiration rate
Our atmosphere (air) is composed of _____ nitrogen and _____ oxygen, while the remaining 1% is composed or argon, CO2 and other gases
78%; 21%
Optimum temperature for home freezing is about __________
-18 degrees C
Most raw vegetables can be stored for only a short period of time, even at -20 degrees C due to changes in sensory properties as a result of __________ activity
Enzyme
Name the two indicator enzymes for blanching:
Catalase and peroxidase
Advantages of blanching:
Fix colour, ease of packaging, decrease enzyme activities, decrease microorganisms
Disadvantages of blanching:
Loss of texture, flavour, nutrients by heating and loss of water-soluble vitamins