The document discusses the application of low-temperature preservation techniques for food, primarily refrigeration and super chilling, which help to slow down microbial growth and biochemical reactions. It outlines the principles of mechanical refrigerators and cryogenic systems, detailing their components and functioning. Additionally, it addresses the effects of chilling on food quality, potential undesirable consequences of improper chilling, and the benefits of super chilling for extending shelf life and maintaining food quality.

1. CHILLING AND ITS APPLICATION
CHETAN LAL
PROCESSING AND FOOD ENGINEERING

2. PRESERVATION BY LOW TEMPERATURE
The use of low temperature to preserve foods is based upon that
facts that the activities of food borne microorganisms and enzyme
reactions can be slow down or stopped at temperature above
freezing temperature and generally stopped at subfreezing
temperatures.
Low temperature can be produced by:
1. Refrigeration or chilling.

3. CHILLING
Preservation of food at temperature above
freezing and below 15 °C is known as
refrigeration or chilling.
Chilling is a short term process of
preservation.
It is used to reduce the rate of biochemical
and microbiological changes and hence to
extend shelf life of fresh processed foods.
It causes minimal changes to sensory
characteristics and nutritional properties of
foods.

4. CHILLING RETARDS
 Growth of microorganisms.
 Chilling retards spoilage and prevent food poisoning
by slowing the growth of microbes during storage.
 Postharvest and post slaughter metabolic activities of
plant and animal tissues respectively.
 Deteriorative chemical reaction, including enzyme
catalysed oxidative browning or oxidation of lipids
and chemical changes associated with colour
degradation, autolysis of fish and loss of nutritive
value of foods.

5. CATEGORIES OF CHILLED FOOD
According to storage temperature range :
• -1 °C to 1 °C (fresh fish, meats, sausages, smoked
meat and ground meat).
• 0 °C to 5 °C (pasteurization milk, canned meat,
cream, yoghurt, salad, sandwiches, baked, foods,
soups and sauces).
• 0 °C to 8 °C (soft fruit and fruit juices, cooked rice
hard cheese and butter).

6. CHILLING EQUIPMENT
1. MECHANICAL REFRIGERATORS.
2. CRYOGENIC SYSTEMS.

7. 1. MECHANICAL REFRIGERATORS
 A mechanical refrigerator, also known as a household refrigerator, is
a common appliance used to preserve food and beverages at low
temperatures.
 Mechanical refrigerators have four basis elements: an evaporator, a
compressor, a condenser and an expansion valve.
 A refrigerant circulates between the four element of the refrigerator,
changing state from liquid to gas and back to liquid.

8. MECHANICAL REFRIGERATORS: COMPONENT
 COMPRESSOR: This is the heart of the refrigerator. It compresses the
refrigerant gas, increasing its pressure and temperature.
 CONDENSER: The compressed refrigerant gas flows through the condenser,
where it releases heat to the surrounding environment. This heat is typically
expelled to the back or bottom of the refrigerator.
 EXPANSION VALVE: The refrigerant gas, now a liquid, passes through the
expansion valve, where it expands rapidly and cools down significantly.
 EVAPORATOR: The cold refrigerant gas flows through the evaporator coils,
which are located inside the refrigerator. As the refrigerant gas absorbs heat
from the inside of the refrigerator, it evaporates back into a gas.
 REFRIGERANT: This is a special fluid that circulates through the

9. MECHANICAL REFRIGERATORS: WORKS
 COMPRESSION: The compressor compresses the refrigerant gas, increasing
its pressure and temperature.
 CONDENSATION: The compressed refrigerant gas flows through the
condenser, where it releases heat to the surrounding environment.
 EXPANSION: The refrigerant gas, now a liquid, passes through the
expansion valve, where it expands rapidly and cools down significantly.
 EVAPORATION: The cold refrigerant gas flows through the evaporator coils,
which are located inside the refrigerator. As the refrigerant gas absorbs heat
from the inside of the refrigerator, it evaporates back into a gas.
 REPEAT: The cycle then repeats, with the compressor compressing the

10. 2. CRYOGENIC SYSTEMS.
 A cryogenic system refrigerator, also known as a cryofreezes or
cryogenic freezer, is a specialized refrigeration unit capable of
maintaining extremely low temperatures, typically below -150°C (-
238°F).
 Cryogenic chillers use solid carbon dioxide, liquid carbon dioxide and
liquid and liquid nitrogen.
 Solid carbon dioxide remove latent heat of sublimation and liquid
cryogens remove latent heat of vaporisation
VARIOUS APPLICATIONS, INCLUDING:
• Food preservation, industrial application, medical and biological

11. EFFECT ON FOOD
 The most significant effect of chilling on the sensory
characterises of processed foods is hardening due to
solidification of fats and oils.
 Other effect include enzymatic browning, lipolysis, colour
and flavour deterioration and retro gradation of starch to
cause staling of bread, protein denaturation, vitamin
degradation.
 Losses of vitamin C in selected vegetables during cold
storage.
Produce days 0°C 0°F losses (%)
asparagus 1-7 1.7-0 35-32 5-50
Broccoli 1-4 7.8-7.8 46-46 20-35
Green
beans
1-4 7.8-7.8 46-46 10-50
spinach 2-3 0-1.1 32-3 5-7

12. DESIRABLE CONSEQUENCES OF
CHILLING TEMPERATURE
 Growth of mesophilic and thermophilic microbes is greatly
retarded at chilling temperature. Psychotropic microorganism, of
course, grow well in the range of 0 °C to 15 °C but is much slower
in this range.
 Rate of respiration and ripping usually declines as the
temperature is reduced below 4 °C in this case of climacteric
fruits.

13. EFFECT OF TEMPERATURE ON
RATES OF RESPIRATION IN FRUITS
AND VEGETABLES
Commo
dity
0 °C 4.5 °C 15.5 °C
Apples 300-1500 600-2700 2300-7900
Peas (green) 8200-8400 1300-16000 39300-44500
Strawberries 2700-3800 3600-6800 15600-20300
British thermal unit (Btu) per ton 24
hr at:
1Btu = 1055.06
Joule

14. UNDESIRABLE CONSEQUENCES OF CHILLING
TEMPERATURES
 COLD SHORTENING
• Animal muscle which is exposed immediately after slaughter
can undergo a detrimental occurrence known as cold
shorting if it is promptly cooled to a temperature range of 0
°C to 5 °C.
 CHILLING INJURY
• A substantial number of fruit and vegetables especially those
of tropical or subtropical origin, develop a physiological
disorders when exposed to temperature but above freezing
temperature.

15. SUPER CHILLING
 Super chilling is one of the method that can be used to
maintain food products at a low temperature.
 Generally, super chilling is positioned between freezing and
refrigeration (conventional chilling), where the surrounding
temperature of a food product is lower to -1 °C to +4 °C, by
means of slurry ice or in super chilled chambers without ice.
 Super chilling is defined as a technology where food is stored
just below the initial freezing temperature.
 Super chilling is that where temperature of food is maintained
below °C but ice crystals are not generated.

16. DEFINITION OF SUPER CHILLING
 Super chilling is that where temperature of food is maintained below
0 °C but ice crystals are not generated. (ando et al. 2004)
 Super chilling is definition as a technology where food is stored just
below the initial freezing temperature. (beaufort et al. 2009)

17. PROCESSING STEPS FOR SUPER
CHILLING OF FISH/SEAFOOD

18. SHELF LIFE ASPECTS IN
RELATIONSHIP TO SUPER
CHILLING TECHNOLOGY
 SUPER CHILLING OF FISH: with the reduction of temperature from -1
°C to -3 °C, the shelf-life increased from 21 to 35 days.
 SUPER CHILLED SALMON: shelf-life double at storage temperature of -
4 °C to -3.6 °C compared to ice chilled storage with respect to microbial and
chemical analysis.
 SUPER CHILLED PORK ROASTS: shelf life of at least 16 weeks
compared to 2 weeks for the chilled products .

19. QUALITY ASPECTS IN RELATION TO SUPER
CHILLING TECHNOLOGY
 Storage of cold-smoke salmon at -2 °C for 1 days did not have any
serious consequences on the quality compared to control (absence of
super chilling).
 During super chilled storage of Kurume prawn, the brightness of tail
colour could be retained compared to traditional refrigeration.
 Drip loss was found to be lower in super chilled samples than in
chilled sample both in cod and salon fillets as well as in pork roasts.