How to preserve foods by using low temperature treatment.

1. Submitted to- Dr. Anil Chauhan
Submitted by- Anjali Jaiswal
DSFT, IAS BHU
ADVANCES IN PROCESSING AND
PRESERVATION BY REFRIGERATION

2. FOOD PRESERVATION AT LOW
TEMPERATURE
 Temperature management is an important tool to control both
physical and biological deteriorations in foods.
 Low- temperature treatment applied during handling,
transportation, and storage is the easiest and most effective
method to extend the shelf life without losing quality.

3. Cont…
 Low- temperature treatment can be defined as removing heat
from the foods, which consequently decreases the temperature
or can change the state from water to ice.
 Low temperature (t) can be combined with other preservation
techniques (hurdles) for effective preservation.

4. Low temperature can be produced by :
 1) Refrigeration or Chilling
 2) Freezing

5. REFRIGERATION
 Preservation of foods at temperature above freezing and below 150C is
known as Refrigeration or Chilling.
 It is used to reduce the rate of biochemical and microbiological changes so
that the ‘ shelf life ‘ of fresh and processed food.
 Chilling causes minimal changes to sensory characteristics and nutritional
properties of foods.

6. REFRIGERATION RETARDS
 Growth of microorganisms
 Moisture loss
 Post- harvest and post slaughter metabolic activities of plant and animal
tissues respectively.
 Deteriorative chemical reactions, including enzyme catalyzed oxidative
browning or oxidation of lipids.
 Chemical changes associated with color degradation, autolysis of fish and
loss of nutritive value of foods.

7. Categories of Chilled Foods
According to storage temperature range:
 -1oC to 1oC
 Fresh Fish
 Meats
 Sausages
 Smoked Meat
 Ground Meat

8. .
 0oC to 5oC
 Pasteurized Milk
 Canned Meat
 Cream
 Salad
 Sandwiches
 Baked foods
 Soup and sauces
 Yogurt

9. .
 0oC to 8oC
 Soft Fruits
 Fruit Juices
 Cooked Rice
 Butter

10. 3 Categories of Refrigeration Systems
 High Temperature Systems
(between -3.9oC to 7oC or high) used for air conditioning and cold storage
equipment.
 Medium Temperature Systems
(between -3.9oC to -17.8oC) used for food storage and other applications
 Low Temperature Systems
(-17.8oC or lower)

11. Use of Refrigeration/ Chilling
Temperature
 Refrigerators and food displaying cabinets
 Commercial Cold Stores
 Controlled Atmosphere Storage facilities (CA Storage)

12. Objectives of Cooling Foods
 A fall in temperature by 10oC reduces the rate of the reactions by one-half,
thus life of a food could be doubled by merely lowering its temperature by
10oC or quadrupled by reducing 20oC from ambient temperature.
 Bread is cooled after baking to facilitate slicing.
 Beef is cooled after slaughtering for ageing to improve its sensory
characteristics.
 In carbonated beverages, water is cooled before carbonation to increase
the solubility of carbon dioxide.

13. Pre- treatment of Food for Low
Storage of Temperature
 Food raw materials get contaminated from different sources when they are
gathered, harvested or slaughtered.
 Beef carcasses are washed, dewatered and stacked in chambers containing
ultraviolet lamps.
 Eggs are dipped in suitable mineral oil 12 to 14 hours after laying, this
treatment retards dehydration as well as loss of carbon dioxide and
maintains quality of eggs, when brought inside the cold store.
 Fruits are stored for over- ripe and under- ripe ones.

14. Cont…
 Vegetables are washed, drained and then stored.
 Lemons, papaya or nectarines are immersed in hot water at 46 to 54oC for
1- 4 mins.
 Cucumbers and root crops are waxed to improve their appearance and
keeping qualities.

15. .
 Chemicals;
 Fruits and vegetables are treated with chlorine, acetates, ozone,
sulfur dioxide, methyl bromide to prevent growth of microorganisms.
 Ripening of plantains is retarded by application of purafil and
ripening of mangoes is retarded by application of 2, 4, 5-
trichlorophenoxy acetic acid.
 Sprouting of onions, potatoes, carrots is prevented by the application
of phenyl carbamates, maleic hydrazide or vapors of nonyl alcohol.
 Ethylene gas is often used as a color modifier to degreen citrus fruits.

16. .
 Irradiation;
 Sterilize the storing chambers, equipped with ultraviolet lamps.
 Meat is often irradiated to destroy the surface microflora and
parasites.

17. Cold Storage Procedures
 At home;
(onions, garlic, ginger, potatoes are stored in cool corner of house)
 In Refrigerators
(meat, fish , eggs and other perishable foods are stored in refrigerators at low
temperature 4-10oC, fruits and vegetables can also be stored but must be washed
and dewatered before storage)
 Cold Stores;
(fruits, vegetables and tubers are stored in large capacity cold stores)

18. Factors Affecting Cold Storage of
Foods
 Temperature
 Relative Humidity
 Composition of Storage Atmosphere
 Ventilation

19. Temperature
 The refrigeration storage temperature depends on;
 Nature of food
 Estimated desired period of storage
 Composition of storage atmosphere
 Pre- treatment of raw material
 1 ton of green beans, sweet corn, okra or green peas stored for 24 hours at
4.5oC generate over 252 kilocalories.
 1 ton carrots or potatoes stored for 24 hours at 4.5oC generate over 504 to
1260 kilocalories.

20. Cont…
 1 ton of grapefruits, lemons, oranges, cabbage, onions and tomatoes
stored for 24 hours at 4.5oC generate over 504 to 1260 kilocalories.
 Animal tissues, firm, ripe fruits and vegetables (stored at optimum chilling
temperature and relative humidity for less than 2 weeks)
 Beef, mutton, poultry, fish, lemons, nectarines, cabbage, carrots, green
peas and spinach (stored at just above freezing temperature for maximum
storage life)
 Oranges, pineapples and potatoes (stored at 2 to 7oC)

21. Cont…
 Bananas, grapefruits, lemons, limes, mangoes, tomatoes, green beans,
cucumbers and sweet potatoes (stored at 7 to 13oC for maximum life)
 Good insulation
 Insulation material should be non- toxic, strong and with low heat
conducting properties.
 Temperature difference between refrigeration coils and storage
atmosphere (smaller temperature difference is preferable because large
temperature difference promotes vapor condensation on cooling coils)

22. Relative Humidity
 High R.H encourage Microbial Growth
(moulds and yeast grow in relative humidity of 85-90% and 90-92%
respectively, whereas, bacteria grow on food surface at near saturation)
 Low R.H result in moisture loss, wilting in fruits and vegetables, damage to
appearance in animal tissues, economic losses.
 Optimum R.H of a particular material depends on the storage temperature.
Optimum R.H of meat is 92% at 0oC, 88% at 2.2oC and 75% at 4.4oC.

23. Composition of Storage Temperature
 O2 is decreased in storage atmosphere from 21% to 10%
 CO2 is increased in storage temperature from 0.04% to above 10%
 Ozone may also be used where high R.H is applied, to control
microorganisms (e.g. eggs can be kept well at R.H of 90% in presence of
1.5 ppm ozone, whereas eggs are kept at R.H OF 85% in absence of ozone)
 Controlled Atmosphere Storage (CA Storage)

24. Ventilation
 To prevent stale odors, flavors and to remove them from atmosphere
 To maintain uniform temperature and relative humidity
 To maintain uniform product composition in storage atmosphere
 If proper ventilation and air circulation is not provided then food placed
in high relative humidity may undergo microbial decomposition

25. Desirable Consequences of Chilling
Temperature
 Growth of Mesophilic and Thermophilic microbes is greatly retarded at
Chilling temperature
 Psychrotrophic microorganisms can grow in range of 0oC to 15oC but this
growth rate is much slower
 Rate of respiration and ripening usually declines as the temperature is
reduced below 4oC (in case of climacteric fruits)

26. Undesirable Consequences of Chilling
Temperature
 Chilling Injury
 It is damage to plant parts caused by temperatures above the freezing
point (32oF, 0oC). Plants of tropical or subtropical origin are most
susceptible to chilling injury.
 Chilling- injured leaves may become purple or reddish and in some cases
wilt. Both flowers & fruit of sensitive species can be injured
 Symptoms include surface lesions/ pitting, internal discoloration, failure to
ripen normally and increased susceptibility to decay organisms such as
Alternaria.

27. Super- Chilling
 It is the type of chilling in which food is stored just below the initial
freezing temperature (1 to 2oC)
 Perishable foods like fish & meat are treated with super chilling technique
 Storing food at chilling temperature has three main advantages:
 Maintaining food freshness
 Retaining high food quality
 Supressing growth of harmful microbes

29. Conclusion
 Low temperature preservation provides longer shelf life of food.
 It is carried out at above freezing and below 15oC.
 Refrigeration reduce the rate of biochemical and microbiological changes
into the food.
 Once the food is drawn out from refrigerate condition the surviving
microorganisms can resume their growth and function, causing disease or
spoilage if the proper conditions for microbial growth prevail.

30. References
 https://www.tandfonline.com/doi/abs/10.1080/10408398.2020.1770687
 http://www.foodpreserving.org/p/refrigeration.html
 https://www.uscooler.com/blog/refrigeration-and-freezing-for-food-
preservation/

31. .
THANKYOU