1. Presented By: Sugam Birthare M. Tech (FT) 16081014
Preservation: Storage by low temp., liquid nitrogen, agar slopes and dehydration Department of Food Technology
Presented By: Sugam Birthare
M. Tech (FT)

2. Content: Introduction Why food needs to be preserved?
Types of preservation
Storage at reduced temperature
Storage under liquid nitrogen
Storage on agar slopes
Storage in a dehydrated form
Reference

3. Introduction:
It is an action or a method of maintaining foods at a desired level of properties/characteristics or nature for as long as possible.
By use of specific thermal and non-thermal processing techniques to minimize microbial spoilage and extending the shelf-life of foods.
Therefore, several methods have been developed for maintaining the organisms in viable conditions over a long period of time. These methods vary according to strains.

4. Why food needs to be preserved?
To preserve quality and nutritive values of foods
To overcome inappropriate planning in agriculture
To prevent spoilage and eliminate waste
To produce value-added products, and
To provide variation in diet

5. Types of preservation techniques:
Storage at reduced temperature
Storage under liquid nitrogen
Storage on agar slopes
Storage in a dehydrated form

6. Storage at reduced temperature:
The use of low temperatures to preserve foods is based upon the fact that the activities of food- borne microorganisms and enzyme reactions can be slowed down and/or stopped at temperatures above freezing and generally stopped at subfreezing temperatures.
Low temperature can be produced by:
Refrigeration or chilling
Freezing

7. Preservation of food by chilling:
Preservation of foods at temperatures above freezing and below 15ºC is known as refrigeration or chilling.
It is used to reduce the rate of biochemical and microbiological changes and hence to extend shelf life of fresh and processed foods.
It causes minimal changes to sensory characteristics and nutritional properties of foods.

8. Categories of chilled food:
According to storage temperature range:
-1ºC to 1ºC (fresh fish, meats, sausages, smoked meat and ground meat).
0ºC to 5ºC (pasteurized milk, canned meat, cream, yoghurt, salad, sandwiches, baked foods, soups and sauces).
0ºC to 8ºC (Soft fruits and fruit juices, cooked rice, hard cheese and butter).

9. Preservation of food by freezing:
Freezing is the unit operation in which the temperature of a food is reduced below its freezing point and a proportion of the water undergoes a change in state to form ice crystals.
Freezing process is a combination of the beneficial effects of low temperature at which micro-organisms cannot grow, chemical changes are reduced and cellular metabolic reactions are delayed.

10. Theory of freezing:
Sensible heat is first removed to lower the temperature of food to the freezing point.
Heat produced by respiration in case of fresh foods (fruits and vegetables) is also removed.
Then latent heat of crystallisation is removed to form ice crystals.
The latent heat of crystallisation of other components of food (e.g., fats) is also removed.

11. Freezing curve of food:

12. Storage under liquid nitrogen:
Storage under liquid nitrogen also known as cryopreservation.
Cryo is Greek word. (krayos – frost).
It can be done :
Over solid carbon dioxide (at -79 degree)
Low temperature deep freezer (at -80 degree )
In vapor phase nitrogen (at -150 degree)
In liquid nitrogen (at -196 degree) Cryopreservation

13. Cont.:
The metabolic activities of micro-organisms may be reduced considerably by storage at the very low temperatures (-150° to -196°) which may be achieved using a liquid nitrogen refrigerator.
Fungi, bacteriophage, viruses, algae, yeasts, animal and plant cells and tissue cultures have all been successfully preserved.
The technique involves growing a culture to the maximum stationary phase, resuspending the cells in a cryoprotective agent (such as 10% glycerol) and freezing the suspension in sealed ampoules before storage under liquid nitrogen.

14. Storage on agar slopes:
All microbiology laboratories preserve micro- organisms on agar slant. The slants or slopes are incubated for 24hr or more and are then stored in a refrigerator (5°) or a freezer (- 20).
These cultures are periodically transferred to fresh media. Time intervals at which the transfers are made which varies with the origin and condition of growth.
The agar slants are inoculated and incubated until good growth appears.

15. Cont.:
They are then covered with sterile mineral oil to a depth of 1 cm above the tip of slant surface.
Many bacterial species can preserved by covering the growth on the agar slants with sterile mineral oil.
Oil reduces the loss of water and also slow down the exchange of gas within organism and surrounding.

16. Storage in a dehydrated form:
Both the terms “drying” and “dehydration” mean the removal of water.
“Drying” usually describes the process of drying under sunshine or open air. The other term, dehydration, usually describes the removal of moisture by applying artificial heat current under controlled conditions.

17. Cont.:
Dehydration can be done by two following methods: Dried cultures and lyophilization.
Dried soil cultures have been used widely for culture preservation, particularly for sporulating mycelial organisms.
Moist, sterile soil may be inoculated with a culture and incubated for several days for some growth to occur and then allowed to dry at room temperature for approximately 2 weeks.
The dry soil may be stored in a dry atmosphere or, preferably, in a refrigerator.
Silica gel and porcelain beads are suggested as alternatives to soil.

18. Cont.:
Lyophilization, or freeze-drying, involves the freezing of a culture followed by its drying under vacuum, which results in the sublimation of the cell water.
The technique involves growing the culture to the maximum stationary phase and resuspending the cells in a protective medium such as milk, serum or sodium glutamate.
A few drops of the suspension are transferred to an ampoule, which is then frozen and subjected to a high vacuum until sublimation is complete, after which the ampoule is sealed.
The ampoules may be stored in a refrigerator and the cells may remain viable for 10 years or more.

19. Cont.:
Lyophilization is very convenient for service culture collections because, once dried, the cultures need no further attention and the storage equipment (a refrigerator) is cheap and reliable.
Overall, the technique appears to be second only to liquid nitrogen storage and even when liquid nitrogen is used makes an excellent insurance against the possibility of the breakdown of the nitrogen freezer.

20. Reference:
Principles of fermentation Technology, by Whittaker.

21. Thank You!
sugam