Low-Temperature Treatment as a Method of Food Preservation

Controlling temperature is a crucial strategy for preventing food degradation, both biologically and physically.

The simplest and most efficient way to increase shelf life without compromising quality is to apply low-temperature treatment during handling, shipping, and storage.

The process of treating food at low temperatures involves extracting heat energy from the food, which either lowers the temperature or transforms the food's condition from liquid to solid. For efficient preservation, low temperature (t) can be paired with other preservation methods (hurdles).

Traditional low-temperature food preservation techniques include freezing and refrigeration.

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Table of Contents

• A. Refrigeration
• Principle of refrigeration
• Requirements for Refrigerated storage: 
• Application of Refrigeration 
• Limitations of Refrigerated storage:
• B. Chilling
• C. Freezing
• Principle of freezing 
• Stages of freezing
• Types of freezing
• Effect of slow freezing
• Application of freezing for food preservation
• Types of conventional freezing methods
• The quality of frozen foods depends upon the following factors:

A. Refrigeration

• Storage at a temperature above the freezing point of food is referred to as refrigeration.
• Between 16°C and -2°C is the freezing refrigeration temperature range.
• According to the kind of food, commercial and residential refrigerators are typically run from 0 to 7.2°C.
• Perishable goods can be preserved for days or weeks with refrigeration.
• This method aids in inactivating the enzyme, which helps to prevent food from accelerated degradation but does not necessarily kill bacteria.
• This method aids in preserving the inherent organoleptic and qualitative characteristics of many foods.

Principle of refrigeration

Low temperatures inhibit microbial growth and slow down chemical and enzymatic reactions.

Requirements for Refrigerated storage: 

1. regulated low temperature
2. circulation of air
3. humidity regulation
4. gas atmosphere modification

Application of Refrigeration 

It is relevant at every stage of the food supply chain, including shipping, receiving, storing, and retailing.

for the purpose of preservation;

1. Raw fresh foods: Fruits, vegetables, meat, fish, and eggs
2. Rice, dal, curry, and other prepared dishes are processed foods.
3. canned goods
4. Beverages and drinks

Limitations of Refrigerated storage:

• Fruits and vegetables can suffer "chill damage" if the refrigeration temperature is not maintained.
• Poor colours occur from the natural ripening enzyme's reduced activity when bananas and tomatoes are stored below 13 degrees Celsius.
• The issue of food taste exchange can also arise when goods are stored in the refrigerator.
• Under refrigeration, vitamin C and other nutrient losses might be observed.
• Some goods, like bread, don't need to be chilled.

B. Chilling

It is comparable to refrigeration in that the temperature is above the freezing point of the food and varies from 0°C to 8°C.

S.N.	Temperature	Foods
1.	±1°C	Fresh fish, meat, sausage, smoked meat, breaded fish
2.	0°C to 5°C	Canned meat, milk, cream, yogurt, salads, pasta, soup, pizza, pastries, cakes, unbaked dough, etc.
3.	0°C to 8°C	Fully cooked meat, butter, cheese, fruit juices, vegetables, cooked rice, etc.

C. Freezing

• The term "freezing" describes the process of storing food in a frozen state by keeping the temperature below the freezing point.
• Typically, a temperature of -18°C or below is required for successful freezing.
• Because most infections do not develop below 3.3°C and food spoiling organisms do not thrive below -9.5°C, microbiologically speaking, -18°C storage is not necessarily necessary. However, the use of -18°C is adequate to halt enzymatic degeneration and to sluggish nonenzymatic process, with certain exceptions.
• Foods may be preserved for months or even years by freezing provided the right packaging is used.

Principle of freezing 

At temperatures over 10°C, food-spoiling bacteria proliferate quickly, but psychrotrophs thrive below 0°C as long as there is still water that isn't frozen. So, making water inaccessible by turning it into a crystal form can stop microbial development or, to some extent, kill microbial cells.

Water crystallisation serves to raise the solute concentration, which in turn helps to raise osmotic pressure or lower water activity. Low temperatures reduce the amount of enzyme activity, chemical reactions, and microbial development.

Stages of freezing

The size of the ice crystals affects the quality of frozen food, and there are many types of freezing depending on how the ice crystals form:

Types of freezing

1. Slow freezing
2. Rapid freezing

S.N.	Process characteristic	Slow freezing	Rapid freezing
1.	Rate of decreasing temperature	≤ 2°C / min.	≥10°C / min.
2.	Ice Crystal size	Large	Small
3.	Location of ice crystals	Extracellular	Intracellular
4.	Cell damage	Shrinkage of cell	Less damage
5.	Drip loss on thawing	More drip loss	Less drip loss
6.	Quality	Less food quality	Good food quality with better texture and flavor

Effect of slow freezing

Cells may burst if the freezing rate is too low, releasing nutrients that drip throughout the thawing process and reducing the food's organoleptic and nutritional value.

Application of freezing for food preservation

Food	Water content (%)	Freezing point (°C)
Egg	74	-0.5
Meat	55-70	-1.7 to -2.2
Milk	87	-0.5
Fruits	87-95	-0.9 to -2.7
Vegetables	78-92	-0.8 to -2.8

Types of conventional freezing methods

1. Plate freezing (contact with the cooled surface)
2. Immersion freezing (contact with the cooled liquid)
3. Cabinet freezing (contact with the cooled gas)

• Room or cabinet freezing
• Air-blast freezing
• Tunnel freezing
• Spiral freezing
• Fluidized Bed freezing
• Belt freezing

D. Cryogenic freezing (use of cryogenic liquid)

S.N.	Types of freezing methods	Food preserved
1.	Plate freezing	Meat steaks, fish fillets, leafy vegetables
2.	Immersion freezing	Canned foods, chicken, fruits, tomato slices, orange segments
3.	Cold room	Beef carcass, chicken, fruits, vegetables
4.	Air blast freezing	Fruits, vegetables, fish fillets
5.	Tunnel freezing	Grains, soybean, fish fillets
6.	Fluidized-bed	Carrot cubes, peas, shrimp, strawberries
7.	Cryogenic	Ice cream, shrimp, berries

The quality of frozen foods depends upon the following factors:

• fresh food quality
• composition of food
• Pretreatment techniques
• choice of freezing techniques
• Rate of freezing
• outstanding hygiene standards
• packing situation
• process of thawing