preservative

VAN LANG UNIVERSITY
ENGLISH FOR BIOTECHNOLOGY




Teacher: BA. Dương Thị Như Hiền
Students: Trương Thị Thanh Diễm
Lâm Thị Tú Mi
Bùi Thị Hồng Phúc
Hồ Thị Hương Thảo
Nguyễn Thị Khánh Tuyên
Lê Tấn Hưng
FORMS OF VEGETABLE
PRESERVATION
1)Freezing
2)Drying
3)Canning
4)Salt & sour vegetable
5)Other
#
• Discover food preservation techniques to
store vegetables many months. Dry and
store vegetables. Preserving garlic, onion,
shallot, beans...How to for storing
vegetables.
• Food preservation and vegetable storage
techniques including canning vegetables,
freezing, pickling and drying or curing.
•
Storing vegetables properly can extend your

food supply for many months.
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1) Freezing &
blanch
#
•
Storage at low temperature slows many of
the enzyme reactions involved in spoilage
and reduces the growth rate of
microorganisms (though it does not kill
them). To minimize microbial growth,
refrigerators should be kept at 0
0
C to 4
0
C
and freezers at or below 0
0
C. Refrigeration
is advantageous because it does not cause
chemical or physical changes to food.
#
0
0
C-4
0
C
low temperature inhibits enzyme activity & microbial growth
below 0

0
C
Freezing it does not cause chemical or physical changes to food.
the water in vegetables expands and forms ice crystals
The structure of plant and animal cells are disrupted


#
The greatest disadvantage
of freezing is that the water
in food expands and forms
ice crystals. The ice
crystals formation disrupts
the structure of plant and
animal cells, giving frozen
food a softer texture after
thawing. Newer
technologies in which
freezing occurs more
rapidly help minimize this
problem: faster freezing
means that smaller ice
crystal form, resulting in
less damage to cells.
#
• Preserving vegetables by freezing retains
more of the vegetable's nutrient value than
canning. While canning may be more
economical, freezing preserves more of the
vegetable’s nutrient value.

• Tips for Vegetable Freezing Success:

Use young, tender vegetables at their peak.

Freeze as soon after harvesting as possible.

Use the best quality freezer bags or
containers to prevent freezer burn
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
After blanching, cool vegetables immediately in
ice water for the same amount of time as you used
for blanching.

Can conveniently stack bags in a box before
putting into the freezer.

Label your bags with the vegetable name and the
date.

Use your frozen vegetables within 8-12 months for
best flavor and nutrients.

For blanching times of specific vegetables.
#
• Freezing vegetables usually requires
blanching in boiling water, cooking, or
steam blanching prior to freezing. These are
the blanching times for common vegetables:


Beets – Remove all but 2 inches of the top; Don’t
blanch – cook until tender; Chill; Then slice and
freeze.
 Carrots – Trim, wash and scrape the carrots; dice or
slice them; blanch for 2 minutes.
 Cabbage – Blanch wedges for 3 minutes; shredded
for 1 ½ minutes.

Ect…

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Tomatos
Corns
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2) Drying
#
•
Drying reduces an item to roughly 50% of
its original volume and 20% of its original
weight through the gradual elimination of
water.
dehydration
sun drying
Drying

air drying
freeze-drying
Removing the water also decrease the
weight & volume of foods.
Retarding the growth of microorganism &

halting of enzymatic & chemical reactions.
In which foods dry naturally
in which foods is exposed to a blast of hot air
In which frozen food is placed in
vacuum chamber to draw out the
water.
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Freeze dried spring onion
Freeze Dried Green Pepper
Dices