preservationbyheat

2. Blanchin
g:
Blanching is used for variety of purpose. It is defined as
a mild heat treatment applied to tissue (usually plant)
primarily to inactivate enzymes prior to freezing,
drying or canning.

3. Functions of blanching:
1.Inactivate most enzymes.
2.Some cleaning action.
3.Remove substances in some products.
4.Activate some enzymes(if controlled).
5.Removes undesirable odours/flavours.
6.Softens fibrous material and decreasesvolume.
7.Exples air and respiratorygases.

4. 8.Preheating of product prior tocanning.
9.Reduces number of microorganisms

5. Major function of blanching is inactivation of enzymes.
Enzymes can cause rapid change in colour, flavour and
nutritive value of such food products.
Blanching as a pretreatment before drying has many
advantages.
Its helps in cleaning the material and reducing the
amount of micro-organisms present on the surface.
Blanching does not allow effective autoclaving,and
stops the activity of autolytic enzymes.
Fruits are not blanched. As a thumb rule, all those
vegetables which cannot be eaten raw are blanched. Ex:
potatoes

6. Methods of blanching:
Blanching is a delicate processing step. It requires
carefull monitoring of time, temperature and the other
conditions. There are mainly two typical methods of
blanching based on type of heating medium viz. Hot
water blanching and steam blanching use hot waterand
steam as heating medium, respectively. A third type of
blanching system exists which is a combination of hot
water and steam blanching.

7. Hot water
Blanching:
In this method, the cleaned food is subjected to hot
water(85 to 100*c) until the enzymes areinactivated.
Pot blanchers are used at home scale. Generally hot
water blanching is done because of low capital costs
and better energyefficiency.

8. Disadvantages associated with hot water blanching
include loss of water-soluble constituents, risk of
contamination and higher cost of water and disposalof
effluent.

9. Steam
blanching:
In case of steam blanching, the food products isdirectly
exposed to steam, which avoids the loss of food soluble
solids (flavours, vitamins, acids, sugars etc.) to
blanching medium as well as solves the problem of
disposing blanching medium after processing.

10. Steam blanching is advantageous as it results in less
loss of water –soluble constituents, less volume of
waste, easy to clean and sterilize. But it has some
disadvantages
such as higher capital costs, uneven blanching,and
lowefficiency.

11. Blanchers with hot water and steamsystem:
This type involves three step process viz. Product on
conveyer belts is exposed to steam consecutively
followed by contact between food and hot waterand
finally immersion in hot water.

12. Efficacy of blanching:
There are various types of enzymes such aslipoxygenase,
polyphenolase, polygalacturonase and chlorophyllase,
which cause loss of quality and therefore, must be
inactivated. Normally, two heat resistant plant enzymes
such as catalase and peroxidase, are used to evaluate
blanching efficacy, as appropriate time and temperature
is required to inactivate them.