Food Preservation method by Low Temperature – Refrigeration, Chilling, Freezing

Food preservation through low-temperature treatment is a widely used and effective method to extend the shelf life of various food products while maintaining their quality. By carefully managing temperature during handling, transportation, and storage, both physical and biological deteriorations can be controlled, ensuring that the food remains fresh for a longer period.

Low-temperature treatment involves the application of cold temperatures to the food, resulting in the removal of heat energy. This reduction in temperature can slow down or inhibit the growth of microorganisms, enzymes, and other spoilage agents that contribute to food deterioration. Additionally, low temperatures can induce changes in the state of water, converting it into ice, which further helps in preserving the food.

Refrigeration and freezing are two traditional methods of low-temperature treatment widely employed in food preservation. Refrigeration involves storing food at temperatures above the freezing point but below room temperature, typically around 0-5 degrees Celsius (32-41 degrees Fahrenheit). This method is commonly used for perishable food items that have a relatively short shelf life, such as fruits, vegetables, dairy products, and certain meats. By keeping the food chilled, microbial growth is slowed down, enzymatic activities are reduced, and the overall deterioration of the food is delayed.

Freezing, on the other hand, involves lowering the temperature of the food below its freezing point, typically around -18 degrees Celsius (0 degrees Fahrenheit) or lower. Freezing effectively halts the growth of microorganisms and enzymes, preserving the food by putting them in a state of suspended animation. This method is extensively used for a wide range of food products, including meats, seafood, fruits, vegetables, baked goods, and prepared meals. The formation of ice crystals during freezing may cause some changes in texture and quality, but overall, freezing is highly effective in preserving the nutritional value and taste of many foods for extended periods.

Low-temperature treatment can be combined with other preservation techniques, known as hurdles, to enhance the effectiveness of food preservation. These hurdles may include packaging techniques, such as vacuum packaging or modified atmosphere packaging, which create a barrier against microbial contamination and oxidative reactions. Other hurdles can include the use of preservatives, pH adjustment, and high-pressure processing. By combining these techniques with low-temperature treatment, food can be preserved more effectively, ensuring an extended shelf life while maintaining quality attributes such as taste, texture, color, and nutritional value.

A. Refrigeration

• Refrigeration is a widely used method of food preservation that involves storing food at temperatures above the freezing point but below room temperature. The temperature range for refrigeration typically falls between about 0 to 7.2 degrees Celsius (32 to 45 degrees Fahrenheit), depending on the specific requirements of the food being preserved.
• Commercial and household refrigerators are designed to maintain temperatures suitable for various types of food. The freezing compartment of a refrigerator usually operates at temperatures ranging from approximately -2 to -16 degrees Celsius (28 to 3 degrees Fahrenheit), ensuring that food remains in a frozen state.
• Refrigeration is particularly effective in preserving perishable foods for a span of days or weeks. By maintaining low temperatures, the growth of microorganisms is significantly slowed down, which helps to prevent spoilage and extend the shelf life of the food.
• It is important to note that refrigeration does not necessarily kill microorganisms present in the food, but it inhibits their growth and activity. Additionally, refrigeration helps to inactivate enzymes that are responsible for catalyzing chemical reactions in food, such as enzymatic browning or degradation of nutrients. By slowing down these enzymatic processes, refrigeration helps to protect the food from rapid deterioration.
• One of the key advantages of refrigeration as a preservation method is its ability to maintain the organoleptic and quality attributes of many foods. By keeping the food chilled, refrigeration helps to preserve the natural taste, texture, color, and nutritional value of various food products. This is particularly beneficial for perishable items such as fruits, vegetables, dairy products, and certain meats, which are highly sensitive to temperature and can rapidly deteriorate if not stored properly.
• In summary, refrigeration is an effective method of food preservation that involves storing food at temperatures above freezing but below room temperature. By inhibiting microbial growth and enzymatic activity, refrigeration helps to extend the shelf life of perishable foods while maintaining their organoleptic and quality attributes. Whether in commercial or household settings, refrigeration plays a crucial role in ensuring the freshness and safety of food for extended periods.

Principle of refrigeration

The principle of refrigeration is based on the understanding that low temperatures can effectively depress microbial growth, as well as slow down enzymatic and chemical processes in food. By applying cold temperatures, the rate of biological and chemical reactions is significantly reduced, which aids in the preservation of food.

Microorganisms, such as bacteria, yeasts, and molds, require specific temperature ranges to grow and multiply. By subjecting food to low temperatures, microbial growth is suppressed, preventing spoilage and the potential for foodborne illnesses. The cold environment inhibits the metabolism and reproduction of microorganisms, thereby extending the shelf life of perishable foods.

Enzymes are proteins that facilitate various biochemical reactions in food, including ripening, browning, and degradation processes. These enzymatic reactions can lead to changes in taste, texture, color, and nutritional composition, ultimately resulting in food spoilage. However, under low-temperature conditions, enzymatic activity is slowed down. The cold temperatures decrease the rate at which enzymes interact with substrates, reducing the overall impact of enzymatic processes on the food.

In addition to microbial growth and enzymatic reactions, refrigeration also helps to slow down chemical processes in food. Many chemical reactions, such as oxidation and degradation, are temperature-dependent. By subjecting food to low temperatures, the speed at which these chemical reactions occur is reduced. This contributes to the preservation of the food’s quality attributes, including flavor, color, and nutrient content.

Overall, the principle of refrigeration is centered around the ability of low temperatures to suppress microbial growth and slow down enzymatic and chemical processes. By creating a cold environment, refrigeration effectively retards the deterioration of food, extending its shelf life and preserving its quality. This principle forms the basis for the application of refrigeration in various food preservation methods, ensuring that perishable foods remain fresh and safe for consumption.

Requirements for Refrigerated storage: 

1. Controlled Low Temperature:
   • Maintain a temperature range suitable for the specific food being preserved (0 to 7.2 degrees Celsius or 32 to 45 degrees Fahrenheit).
   • Slows down the growth of microorganisms, preserving the freshness and quality of the food.
2. Air Circulation:
   • Ensure proper airflow within the storage area.
   • Prevent the formation of hot spots or cold pockets.
   • Helps maintain a consistent temperature throughout the space.
   • Reduces the risk of temperature fluctuations and ensures uniform preservation of the stored food.
3. Humidity Control:
   • Maintain an appropriate humidity level (typically between 80% and 95%).
   • Prevents moisture accumulation and the growth of molds and bacteria.
   • Avoids excessive moisture loss, preserving the texture and freshness of the food.
4. Modification of Gas Atmosphere:
   • Adjust the gas composition within the storage environment, if necessary.
   • Used for specific food items, such as fruits, vegetables, and meats.
   • Achieved through modified atmosphere packaging or controlled atmosphere storage.
   • Alters the concentration of gases like oxygen, carbon dioxide, and nitrogen.
   • Slows down spoilage-causing organisms or delays ripening processes, extending the food’s shelf life.

By meeting these requirements, refrigerated storage effectively inhibits microbial growth, slows down enzymatic and chemical processes, and extends the shelf life of perishable foods while preserving their quality and freshness.

Application of Refrigeration 

Refrigeration finds application throughout the entire food supply chain, encompassing transportation, warehousing, retailing, and storage. It is employed for the preservation of various types of foods, including:

1. Fresh Foods (Raw):
   • Vegetables: Refrigeration helps to slow down the spoilage of vegetables, maintaining their crispness and nutritional content.
   • Fruits: Cold temperatures help to extend the shelf life of fruits, delaying ripening and preserving their flavor and texture.
   • Meat: Refrigeration is crucial for storing raw meat, preventing bacterial growth and maintaining its quality and safety.
   • Fish: Cold storage helps to preserve the freshness and quality of fish, preventing spoilage and degradation.
   • Eggs: Refrigeration helps to maintain the freshness and quality of eggs, extending their shelf life and reducing the risk of contamination.
2. Processed Foods:
   • Rice and Dal: Refrigeration aids in preserving cooked rice and lentils, inhibiting microbial growth and maintaining their taste and texture.
   • Curry and Other Cooked Items: Cold storage helps to keep prepared curries and cooked dishes fresh for longer periods, reducing the risk of bacterial contamination and maintaining flavor.
3. Canned Foods:
   • Refrigeration is essential for maintaining the quality and safety of canned foods, such as canned fruits, vegetables, soups, and sauces.
   • Cold temperatures help to inhibit microbial growth and maintain the taste, texture, and nutritional value of the canned products.
4. Drinks and Beverages:
   • Refrigeration is commonly used to chill and store various types of drinks and beverages, including juices, soft drinks, milk, and dairy products.
   • Cold temperatures help to preserve the freshness, taste, and quality of these beverages, providing a refreshing and safe experience for consumers.

By applying refrigeration in these applications, the shelf life of perishable foods is extended, reducing food waste and ensuring that consumers have access to fresh and safe food products. Refrigeration plays a crucial role in maintaining the quality, nutritional value, and safety of a wide range of food items throughout the entire food supply chain.

Defects of Refrigerated storage

Defects of refrigerated storage can occur if proper temperature and handling are not maintained. Here are some common issues associated with refrigerated storage:

1. Chill Injury to Fruits and Vegetables:
   • When the refrigeration temperature is not appropriately maintained, fruits and vegetables can suffer from “chill injury.”
   • Chill injury refers to the damage caused by exposure to temperatures below the optimal range for specific produce.
   • Symptoms may include discoloration, water-soaked areas, pitting, and accelerated decay, leading to a loss of quality and shelf life.
2. Negative Effects on Banana and Tomato Quality:
   • Storing bananas and tomatoes under temperatures below 13 degrees Celsius (55 degrees Fahrenheit) can adversely affect their quality.
   • Cold temperatures slow down the activity of natural ripening enzymes in these fruits, resulting in poor color development and altered texture.
3. Flavor Exchange between Foods:
   • Refrigerated storage can lead to flavor exchange between different food items stored in close proximity.
   • Strong odors from one food can be absorbed by other foods, compromising their original flavors and aromas.
4. Loss of Vitamin C and Other Nutrients:
   • Prolonged refrigeration can cause a loss of certain nutrients, including vitamin C, in some food items.
   • Exposure to air and low temperatures can contribute to the degradation of vitamins and other sensitive compounds, reducing their nutritional value.
5. Unsuitability for Certain Foods:
   • Not all food items are suitable for refrigerated storage.
   • Certain foods, such as bread, may undergo undesired textural changes when refrigerated, leading to stale or toughened consistency.
   • It is important to follow specific storage recommendations for each food item to maintain optimal quality and freshness.

B. Chilling

Chilling is a food preservation method that is similar to refrigeration. It involves storing food at temperatures ranging from 0°C to 8°C, which is above the freezing point of the food.

Different temperature ranges within the chilling category are suitable for preserving specific types of foods:

1. ±1°C:
   • Fresh fish, meat, sausage, smoked meat, breaded fish, and other highly perishable items are typically stored at this temperature.
   • The close-to-freezing temperature helps to slow down microbial growth and maintain the freshness and quality of these foods.
2. 0°C to 5°C:
   • Canned meat, milk, cream, yogurt, salads, pasta, soup, pizza, pastries, cakes, unbaked dough, and similar foods fall within this temperature range.
   • The slightly higher temperature ensures that these perishable items remain chilled while preventing freezing, which can adversely affect their texture and quality.
3. 0°C to 8°C:
   • Fully cooked meat, butter, cheese, fruit juices, vegetables, cooked rice, and various other prepared or semi-prepared foods are commonly stored within this temperature range.
   • The slightly broader temperature range provides adequate chilling to maintain the freshness and quality of these items without risking freezing.

Chilling is an effective preservation method as it slows down microbial growth and enzymatic activity, thereby extending the shelf life of perishable foods. It helps to preserve the organoleptic qualities, such as taste, texture, and nutritional content, while ensuring the safety of the stored food.

Proper temperature control and monitoring are crucial when implementing chilling as a preservation technique. Adhering to the recommended temperature ranges for different food categories helps to ensure that the foods remain safe, fresh, and of high quality throughout their shelf life.

Applications of Chilling

Chilling has various applications in the food industry for preserving and storing perishable items. Here are some common applications of chilling:

1. Preservation of Fresh Foods:
   • Chilling is widely used to preserve fresh foods, including fruits, vegetables, meats, and seafood.
   • By storing these perishable items at chilled temperatures, microbial growth and enzymatic activity are slowed down, helping to maintain their freshness and quality.
2. Chilling of Dairy Products:
   • Dairy products such as milk, cream, yogurt, and cheese often undergo chilling to maintain their freshness and inhibit the growth of spoilage-causing microorganisms.
   • Chilling helps to extend the shelf life of dairy products while preserving their taste, texture, and nutritional properties.
3. Chilling of Prepared Foods:
   • Prepared foods, including salads, sandwiches, cooked meats, and other ready-to-eat meals, are commonly chilled to maintain their quality and ensure food safety.
   • Chilling inhibits the growth of bacteria and helps to preserve the freshness and flavor of these foods until they are consumed.
4. Chilling for Beverage Storage:
   • Chilling is frequently used to cool and store a variety of beverages, such as soft drinks, fruit juices, water, and alcoholic beverages.
   • Cold temperatures enhance the sensory experience by providing a refreshing and chilled drink to consumers.
5. Chilling in Bakeries and Pastry Shops:
   • Bakeries and pastry shops often utilize chilling to preserve and maintain the quality of baked goods.
   • Chilling dough, pastries, cakes, and other bakery items can slow down yeast fermentation, reduce enzymatic reactions, and prevent spoilage.
6. Chilling for Food Service and Buffets:
   • In food service establishments and buffets, chilled display cases, refrigerated counters, and cold storage units are used to keep food items fresh and safe.
   • Chilling ensures that perishable foods, such as salads, sandwiches, and cold cuts, maintain their quality and remain at safe temperatures during service.

Overall, the application of chilling is widespread throughout the food industry. By employing appropriate chilling techniques, food professionals can preserve the freshness, extend the shelf life, and maintain the quality and safety of a wide range of perishable food items.

C. Freezing

• Freezing is a food preservation method that involves storing food at temperatures lower than its freezing point, resulting in a frozen condition. Maintaining a temperature of -18°C or below is generally considered ideal for effective freezing.
• From a microbiological standpoint, a storage temperature of -18°C is not strictly required because most pathogens do not grow below 3.3°C, and food spoilage organisms do not grow below -9.5°C. However, storing food at -18°C or below is still recommended as it helps to retard enzymatic deterioration and slow down nonenzymatic reactions, except in some specific cases.
• One of the significant advantages of freezing is its ability to preserve food for extended periods. When food is properly frozen and packaged, it can be preserved for months to years without significant loss in quality. The low temperatures in freezing inhibit microbial growth, enzyme activity, and chemical reactions, thereby maintaining the nutritional value, taste, and texture of the food.
• Proper packaging is crucial in freezing to prevent moisture loss, freezer burn, and the transfer of odors. Packaging methods such as vacuum sealing, airtight containers, or freezer-safe bags are commonly employed to protect the food from freezer-related issues and maintain its quality during storage.
• Freezing is suitable for a wide range of food items, including fruits, vegetables, meats, seafood, baked goods, prepared meals, and more. However, it is important to note that freezing may cause some changes in texture and quality in certain foods, such as the formation of ice crystals or textural changes in fruits and vegetables. Nonetheless, when frozen and stored properly, many foods can be preserved in a high-quality state for an extended period, ready to be thawed and enjoyed when needed.
• In summary, freezing is a highly effective food preservation method that involves storing food at temperatures lower than its freezing point. By inhibiting microbial growth, enzymatic deterioration, and nonenzymatic reactions, freezing can preserve food for months to years. Proper packaging techniques are essential to maintain the quality of frozen foods. Freezing offers convenience and flexibility, allowing individuals to store a variety of foods and enjoy them at their convenience while minimizing food waste.

Principle of freezing 

The principle of freezing in food preservation is based on the understanding that food spoilage microorganisms grow rapidly at temperatures above 10°C (50°F). However, certain microorganisms known as psychrotrophs can grow below 0°C (32°F) as long as there is unfrozen water available to them. Therefore, the key principle of freezing is to make water unavailable for microbial growth by changing its state to a crystal form through the process of freezing.

During freezing, the water present in the food is transformed into ice crystals. This crystallization process helps to reduce the availability of unfrozen water, which is necessary for microbial growth. By making water unavailable, freezing effectively prevents or minimizes microbial growth, inhibiting the spoilage of food.

Another important aspect of freezing is the concentration of solutes. As water freezes and forms ice crystals, the solutes in the food become more concentrated. This increased solute concentration leads to a higher osmotic pressure or a reduction in water activity. These conditions create an unfavorable environment for microbial growth, further inhibiting the growth and survival of microorganisms in the frozen food.

In addition to preventing microbial growth, freezing also slows down enzymatic activity and chemical reactions in food. Low temperatures significantly reduce the activity of enzymes, which are responsible for catalyzing various biochemical reactions. This decrease in enzymatic activity helps to preserve the quality, taste, and nutritional value of the food during frozen storage. Furthermore, chemical reactions that can cause spoilage or degradation of the food are minimized at low temperatures, contributing to the preservation of food quality.

In summary, the principle of freezing in food preservation revolves around changing the state of water to a crystal form, thereby making it unavailable for microbial growth. Freezing also increases solute concentration, reduces water activity, and lowers enzyme activity and chemical reactions, all of which contribute to the preservation of food quality during frozen storage. By effectively inhibiting microbial growth and slowing down deteriorative processes, freezing extends the shelf life of various food products while maintaining their taste, texture, and nutritional value.

Stages of freezing

The process of freezing food typically involves several stages. Here are the common stages of freezing:

1. Pre-Freezing Preparation:
   • Before freezing, the food is often prepared to ensure optimal results.
   • Cleaning, washing, and trimming may be necessary to remove any dirt, debris, or unwanted parts from the food.
   • Peeling, slicing, or cutting the food into desired shapes or sizes can facilitate the freezing process and future use.
2. Initial Cooling:
   • In this stage, the food is subjected to a rapid cooling process to bring its temperature down quickly.
   • Quick cooling helps to minimize the formation of large ice crystals, which can affect the texture and quality of the food.
   • Methods such as blast freezing or flash freezing are often employed to achieve rapid cooling.
3. Freezing:
   • Once the food has been initially cooled, it is transferred to the freezing equipment or storage containers suitable for freezing.
   • The food is placed in a freezer or other freezing units, where it will be exposed to temperatures below its freezing point.
   • As the temperature drops, the water within the food gradually forms ice crystals, causing the food to freeze.
4. Solidification:
   • During this stage, the water within the food completes its transformation into ice, resulting in the solidification of the entire food product.
   • The solidification process helps to lock in the food’s moisture, nutrients, and structure, preserving its quality.
5. Storage:
   • Once the food is completely frozen, it is transferred to long-term storage containers, such as freezer bags, airtight containers, or vacuum-sealed packages.
   • Proper packaging is crucial to protect the food from freezer burn, moisture loss, and contamination.
   • The frozen food is then stored in a freezer or deep freeze at a temperature of -18°C or below to maintain its frozen state.

By following these stages of freezing, food can be preserved effectively, maintaining its quality, taste, and nutritional value for extended periods of time.

Types of freezing

There are two main types of freezing methods used in food preservation: slow freezing and rapid freezing. Here are the characteristics of each method:

1. Slow Freezing:
   • Rate of Decreasing Temperature: ≤ 2°C per minute.
   • Ice Crystal Size: Large ice crystals form during slow freezing.
   • Location of Ice Crystals: Ice crystals primarily form outside the cells (extracellularly).
   • Cell Damage: Slow freezing can cause some shrinkage of the cells, leading to potential damage.
   • Drip Loss on Thawing: More drip loss may occur during thawing due to larger ice crystals damaging cell structures and releasing more moisture.
   • Quality: Slow freezing may result in lower food quality compared to rapid freezing. Texture and flavor may be compromised due to the formation of larger ice crystals.
2. Rapid Freezing:
   • Rate of Decreasing Temperature: ≥ 10°C per minute.
   • Ice Crystal Size: Rapid freezing promotes the formation of small ice crystals.
   • Location of Ice Crystals: Ice crystals are formed predominantly inside the cells (intracellularly).
   • Cell Damage: Rapid freezing causes less cell damage compared to slow freezing, as the smaller ice crystals have less disruptive effects.
   • Drip Loss on Thawing: Less drip loss is observed during thawing due to the smaller ice crystals causing minimal cell damage and moisture loss.
   • Quality: Rapid freezing generally preserves better food quality, including texture and flavor, as the formation of small ice crystals helps to retain the food’s natural attributes.

Effect of slow freezing

Slow freezing can have negative effects on the quality and nutritional value of food. Here is the effect of slow freezing:

1. Cell Rupture and Nutrient Loss:
   • When food is frozen slowly, ice crystals form gradually, leading to larger crystal formation.
   • The slow formation of large ice crystals can cause cell rupture in the food, releasing nutrients and moisture.
   • During the thawing process, these released nutrients drip away, resulting in a loss of flavor, texture, and nutritional value.
2. Deterioration of Organoleptic Properties:
   • Slow freezing can negatively impact the sensory attributes of the food.
   • The release of moisture and nutrients due to cell rupture during slow freezing can lead to changes in texture, causing a loss of crispness or tenderness.
   • Flavor and aroma can also be affected, resulting in a dull or off-flavor in the thawed food.
3. Loss of Nutritional Value:
   • Slow freezing may contribute to a loss of nutritional value in the food.
   • The release of nutrients during slow freezing can result in a reduction of essential vitamins, minerals, and other beneficial compounds.
   • Prolonged exposure to freezing temperatures can also lead to nutrient degradation over time.
4. Formation of Large Ice Crystals:
   • Slow freezing allows for the formation of larger ice crystals within the food.
   • The size and distribution of ice crystals can affect the food’s texture and structure.
   • Large ice crystals can cause damage to the cell structure, resulting in a softer or mushy texture upon thawing.

Application of freezing for food preservation

Freezing is widely employed as a food preservation method due to its ability to extend the shelf life of various food items. Here are some applications of freezing for food preservation based on water content and freezing points:

1. Eggs:
   • Eggs have a high water content of around 74%.
   • Freezing eggs can help to preserve them for a longer period, especially when they are used for baking or cooking purposes.
   • Freezing can also be applied to egg yolks or egg whites separately, providing flexibility for different culinary uses.
2. Meat:
   • Meat typically has a water content ranging from 55% to 70%.
   • Freezing meat at temperatures below its freezing point (-1.7°C to -2.2°C) helps to preserve its quality, texture, and nutritional value.
   • It inhibits the growth of spoilage microorganisms and slows down enzymatic reactions, extending the shelf life of meat products.
3. Milk:
   • Milk has a high water content of around 87%.
   • Freezing milk helps to preserve it for a longer duration, especially when there is excess supply or for use in future recipes.
   • Proper packaging is crucial to prevent off-flavors or separation of milk components upon thawing.
4. Fruits:
   • Fruits generally have a water content ranging from 87% to 95%.
   • Freezing fruits at temperatures below their freezing points (-0.9°C to -2.7°C) helps to preserve their texture, flavor, and nutritional value.
   • Frozen fruits can be used in smoothies, desserts, or as toppings, allowing consumers to enjoy their favorite fruits year-round.
5. Vegetables:
   • Vegetables have a water content ranging from 78% to 92%.
   • Freezing vegetables at temperatures below their freezing points (-0.8°C to -2.8°C) helps to retain their color, texture, and nutritional content.
   • Frozen vegetables can be used in various culinary applications, such as stir-fries, soups, or side dishes, providing convenience and versatility.

Types of conventional freezing methods

Different types of conventional freezing methods are utilized in food preservation. Here are some of the common methods along with the food items they are typically used for:

1. Plate Freezing:
   • In plate freezing, food items come into direct contact with a cooled surface, such as a metal plate or tray.
   • Suitable for preserving meat steaks, fish fillets, and leafy vegetables.
2. Immersion Freezing:
   • Immersion freezing involves submerging the food in a cooled liquid, often a refrigerant or brine solution.
   • Commonly used for preserving canned foods, chicken, fruits, tomato slices, and orange segments.
3. Cabinet Freezing:
   • Cabinet freezing is performed in specially designed cold rooms or cabinets where the food is placed in contact with the cooled gas inside.
   • Suitable for preserving larger food items like beef carcasses, whole chickens, fruits, and vegetables.
4. Air Blast Freezing:
   • Air blast freezing utilizes a high-velocity stream of chilled air to rapidly freeze the food.
   • Used for freezing fruits, vegetables, and fish fillets.
5. Tunnel Freezing:
   • In tunnel freezing, food items are transported on a conveyor belt through a tunnel or chamber where chilled air circulates.
   • Often used for freezing grains, soybeans, and fish fillets.
6. Fluidized Bed Freezing:
   • In fluidized bed freezing, the food is suspended in a rapidly moving cold air stream, creating a fluid-like effect.
   • Suitable for freezing small food items such as carrot cubes, peas, shrimp, and strawberries.
7. Cryogenic Freezing:
   • Cryogenic freezing involves the use of extremely low temperatures achieved by using cryogenic liquids like liquid nitrogen or carbon dioxide.
   • Commonly used for freezing ice cream, shrimp, and berries.

The quality of frozen foods depends upon the following factors:

The quality of frozen foods depends on several factors that influence their taste, texture, appearance, and nutritional value. Here are the key factors that affect the quality of frozen foods:

1. Quality of Fresh Food:
   • The initial quality of the fresh food before freezing greatly influences the quality of the frozen product.
   • Fresh foods that are harvested or sourced at their peak ripeness or freshness are more likely to retain better quality characteristics after freezing.
2. Food Composition:
   • The composition of the food, including its moisture content, fat content, and presence of other components, can impact its freezing and thawing behavior.
   • Foods with high water content or high fat content may have different freezing and thawing characteristics, which can affect their overall quality.
3. Pretreatment Methods:
   • Pretreatment methods, such as blanching, steaming, or blanching, can be employed before freezing to improve the quality of the frozen food.
   • These treatments can help preserve color, texture, and nutrient content, and may also help inactivate enzymes that can cause deterioration during frozen storage.
4. Selection of Freezing Methods:
   • Different freezing methods, such as plate freezing, air blast freezing, or fluidized bed freezing, can impact the quality of frozen foods.
   • The choice of freezing method depends on the specific food item and its desired qualities, such as texture, moisture retention, or minimal cell damage.
5. Freezing Rate:
   • The rate at which the food is frozen can affect its quality.
   • Rapid freezing methods are generally preferred as they promote the formation of smaller ice crystals, which helps retain the food’s texture, moisture, and overall quality.
6. Good Hygienic Practices:
   • Maintaining good hygiene during food handling, processing, and freezing is crucial for preserving the quality of frozen foods.
   • Proper sanitation and prevention of cross-contamination can prevent the introduction of unwanted microorganisms and ensure the safety and quality of the frozen product.
7. Packaging Condition:
   • The packaging used for freezing plays a vital role in maintaining the quality of frozen foods.
   • Packaging materials should be moisture-proof, airtight, and resistant to freezer burn to prevent the loss of moisture, flavor, and nutrients.
   • Proper packaging also prevents contamination and maintains the overall integrity of the frozen food.
8. Thawing Process:
   • The method and conditions used for thawing the frozen food can affect its quality.
   • Slow and controlled thawing methods are generally recommended to minimize moisture loss and maintain the texture and flavor of the food.

By considering these factors and implementing appropriate techniques and practices, it is possible to maintain the quality of frozen foods and ensure that they retain their desired attributes even after storage.

FAQ

References

1. Rahman MS (1999), Handbook of Food Preservation, Marcel Dekker, Inc, NY
2. Potter NP (1987), Food Science, CBS Pub, India
3. Desrosier EN (1963), The Technology of Food Preservation, AVI Publishing Company,New York