Presentation about Freezing mechanism .pdf

Presentation about Freezing mechanism

1. Freezing

2. Freezing
Freezing is a physical method for food preservations causing
a rapid decrease in the initial count of viable organisms.
The carcass should firstly chilled to remove the animal heat,
then quartered and frozen either slowly or rapidly.

3. Freezing:
• Physchrotrophic organisms, are those growing at below
5
o
Cthus capable of causing spoilage of refrigerate foods,
bacteria mainly concerned to genus pseudomonas others as
Achromobacter, flavobacterium, micrococcus, alcaligenes
also may found yeasts and molds of genera
Penicillium
Cladosporium
Sorotrichum.

4. If warm meat is frozen slowly (without previous chilling)
considerable microbial growth may develop before the
temperature of the meat is brought down to freezing
point.
Freezing:

5. Preparation of meat for freezing:
Beef should be chilled at first to remove body heat and then
quartered after 48 hr. and then frozen as units and prefer to be
packed in bags to avoid surface evaporation.

6. Storage of meat:
Meat should not touch wall or floor of refrigerating room to avoid freezer burn.
Storage temperature at -18
o
C. RH 90%.
•Beef has longest storage period.
12 months at -18C, 18 months at -25ºC, 24 months at -30ºC.
•While pork is shorter.
6 months at -18ºC, 12 m at -25ºC, 15 m at -30ºC.
- Prolonged frozen meat appear dry, rancid and less palatable.
- Frozen offals and poultry should be wrapped in grease proof or wax paper to
protect it from storage changes, keep its bloom.

7. Thawing:
The best method is to subject meat to
a temp. 0ºC and RH 70% then
gradually increase temp. to 10ºC and RH 90%
The fore quarter need 65 hrs,
Hind-quarter need 80 hrs for complete thawing.

8. Freezing methods:
It is the cheapest and slowest method
Placing the packaged foods in freezing room (tm. -10ºC to -30ºC)
Not need air speed.
The time required for freezing depend upon
▪The temperature of freezing room
▪Type of food,
▪Size and shape of food package.
Still air freezing:
1

9. Freezing methods:
2
3
Blast freezing, sharp or fast or forced air freezing:
The same as still air except using compressor which pushing air to the
food with air velocity 15 meter/second and temp. –34 to -40ºC so,
it is rapid freezing but this method may cause food dehydration and
freezer burn.
➢uses a liquid coolant (good heat conductors as refrigerants) heat-transfer
medium, with the food either directly or indirectly.
➢Liquids used must be safe-nontoxic-cheap with low viscosity.
➢used for fish, poultry and some meat as spray or fog systems
➢this method prevent oxidative changes but food must be packed to avoid
taste of liquid refrigerants.
Immersion freezing:

10. Freezing methods:
4
5
Cryogenic freezing:
Using of condensed gases such as
liquid nitrogen (-195
o
C) or liquid nitric oxide (-78
o
C), dry ice (-98
o
C) and Freon (-30
o
C).
The meat placed in a room and the vapor of liquid gases pass through it.
It is a rapid freezing.
Best method nontoxic, minimize the oxidative changes less dehydration (less drip loss but
Expensive.
Indirect contact of food and previously cooled plates or walls of metal surface
which is cooled by refrigerants,
The food may be packed in cans or in paper board box and come in contract
with the metal plate which may be movable belt or stationery.
Temp. -17
o
C to -30
o
C/ 4 hrs.
Plate freezing:

11. Effect of freezing on pathogenic microorganisms
and parasite:
•Freezing not destroy all bacteria some bacteria only inhibit its growth until
the condition become favorable reactive again.
•Anthraxbacilliresistant temp at -13
o
C
•Salmonella with sand exposure to -175
o
C 3 days.
•Tubercle bacilli found a life in a carcass frozen at -10
o
C for 2 years.
•Cysticercuscellulose in pork destroyed if stored at -10
o
C 4 days, while
•Cysticrecusbovisin beef need 2 weeks at -10
o
C temp.
•Trichnellaspiralscyst in pork destroyed at -15C / 20 days or 24 hr. at -18
o
C.

13. Changes in frozen meat:
1Physical changes:
a. Muscle plasma (albumin- gloublin) irreversible dehydration on thawing
when meat is frozenbelow-2ºCformation of ice crystals increase the
concentration of these proteins and they become irreversible insoluble in
water even after thawing.
b. Ice crystal formation:
Freezing point of meat lie between -1
o
C to- 1.5
o
C water changed to ice crystals lead to
formation of large ice crystal which lower the quality of frozen meat.

14. Changes in frozen meat:
2Fungal formation:
It is common affections of imported meat due to exposure to dust between shipping, sale and
frequent fluctuation of temp.
a.Stickiness:
Judgment:
•Trimming quick consumption if less extension.
•Total condemnation if more extensive or involved with a Chromobacter group.
The meat surface is sticky to touch due to mold growth.
b. Black spot:

It measures 6-13 mm in diameter. not more than 3 mm depth into meat,
caused by Cladosporum, Penicillium.
grow at 0
o
C to -8
o
C
commonly found in neck, diaphragm, pleura and at legs of beef.
Inside the neck or at thoracic and abdominal cavities of sheep.

15. Fungal formation:
Changes in frozen meat:
2
c. White spot:
Small flat wooly spot at the surface measures 6-13 mm in diameter,
grow well at -2.5
o
C can grow at -8
o
C caused by Sporotrichum carnis.
Judgment:
Removed by wipping the meat surface.
d. Whiskers:
Cottony or fluffy appearance due to collapse of mycelial growth of
Thamnidium elegans and Mucor and Rhizopus spp.
grow at 0
o
C and its more than 2.5 cm in diameter and stop to grow below
-7.5
o
C. Judgment:
Removed by wipping the meat surface.

16. caused by Thamnidium elegans on chilled and frozen meat( Whiskers)

17. Fungal formation: white spots

18. Fungal formation:
Changes in frozen meat:
2
e. Green bluish patches:
Grow at the surface or to depth of 2 mm they caused the green spores of Penicllium spp.
f. Yeast superficial growth:
Slimy meat , lipolysis, bad odor, discoloration
(white – cream – pink – brown) due to pigment formation.
Judgment:
Removed by wiping.

19. Changes in frozen meat:
3Fat rancidity:
fat destruction to free fatty acids and glycerol either by oxidation (oxidative rancidity)
or by the effect of lipase enzyme mainly secreted by mold (lipolytic rancidity).
Brine staining:
4
Contamination of meat with the circulating brine or calcium chloride due to defect in
the joints or leakages of the circulating system resulting inpaleordullgreenish
discolorationofthesurfaceofthecarcasswithbittertaste.
Judgment:
Removed by trimming but if there is extension to pleura or protonium rejected.

20. Changes in frozen meat:
5Freezer burns:
Takes place on the outer surface of imported frozen offal's, mainly liver and kidney as
a result of loss of moisture from the outer tissues due to the carcass is
placed near the opening of cold air duct or
in contact with the refrigerating tubes.
causing dehydration of the surface of the offal's which become
soft, spongy with yellowish batches
can be prevented by
Enclosing the offal's use boxes lined by two layers of aluminum foil
kept boxes not in touch to refrigerating tube or in front of cold air opening.
Judgment:
It unpalatable, unmarketable so need condemnation.

21. Changes in frozen meat:
6Dripping or weeping:
It referring to the presence of a watery blood stained fluid released when thawing meat.
The fluid consists of water, salts, proteins, soluble vitamins, damaged blood cell.
It is undesirable feature resulting from the destruction of muscle cells by ice crystals and
by irreversible changes in muscle plasma which prevent reabsorbtion of these fluids.
The size of ice crystals has a direct effect so the slow freezing which produce large ice
crystals increase the wiping and decrease the palatability of meat.
The rate of thawing is less important than the rate of freezing.

22. Changes in frozen meat:
7Bone taint:
Deep seated spoilage of meat due to anaerobic spore formers bacteria which enter to
the blood from the gut of animal before slaughter and facilitated by exhaustion
such putrefaction is stimulated by body heat and entrance of bacteria before slaughter
to femur pelvic and shoulder regions as synovia is more preferable of high pH 7-8.
grey or blackish-purple color , pronouncing odor .
Judgment:
•If local ➔ require contamination of the affected part.
•If then is extensive putrefaction ➔ condemn the whole quarter.
Prevention: By chilling of carcasses just after slaughtering and immediately after R.M.

23. Freezing
For optimum results in chilling and freezing and to prevent growth
of bacteria the following instructions should be carried out:
1. The initial design of refrigeration room should take in consideration, the
product tenderness, weight loss, spoilage possibility, size of individual units,
space required, rail height, floor, wall surface ……….etc.
2. Temperature must be checked regularly.
3. Avoid over loading carcasses don’t touch each others.
4. Door opening and closing should be minimal.
5. Adequate air flow around the carcasses.
6. Don’t put different species together in the same place.
7. Not make chilling unless after 10 hrs. to avoid cold shortening.
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