FREEZING IN FOOD PROCESSING AND PRESERVATION
- 2. INTRODUCTION A method of food preservation whereby the heat is removed (heat of fusion) from the food, reducing its temperature below its freezing point and a portion of water in food undergoes a change in state to form ice crystals (Aw lowered)
- 3. FREEZING THEORY The theory of freezing refers to the process by which a substance changes from a liquid state to a solid state due to a decrease in temperature below its freezing point. This transition occurs when the kinetic energy of the particles within the substance decreases to the point where they form ordered arrangements, resulting in a solid structure. The freezing point is the temperature at which the solid and liquid phases of a substance are in equilibrium. One of the fundamental principles behind the theory of freezing is thermodynamics, specifically the concept of Gibbs free energy. When a substance undergoes freezing, its Gibbs free energy decreases, indicating a decrease in the system's overall energy and an increase in stability.
- 4. CONT……… The theory of freezing food revolves around preserving it by reducing its temperature to below its freezing point, typically around 0°C (32°F). This process slows down or halts the growth of microorganisms, enzymes, and chemical reactions that cause food spoilage, thus extending its shelf life. Freezing helps maintain the quality, texture, flavor, and nutritional value of food for longer periods compared to other preservation methods. Proper packaging and storage conditions are crucial to prevent freezer burn and maintain food quality during freezing.
- 5. FACTORS TO CONSIDER DURING FREEZING 1. Food Composition: Different foods have varying compositions, such as water content, fat content, and presence of air pockets. Understanding the composition helps determine the freezing rate and the formation of ice crystals, which can affect the quality of the frozen food. For instance, foods with high water content freeze faster but may suffer from texture changes due to ice crystal formation. 2. Thermal Conductivity: This refers to how well heat can transfer through a material. Foods with higher thermal conductivity freeze more quickly and evenly. It's essential to consider this factor to ensure uniform freezing throughout the food item, preventing uneven texture or quality.
- 6. CONT……….. 3. Temperature Difference: The temperature differential between the food and the freezing medium affects the freezing rate. A higher temperature difference generally leads to faster freezing. However, rapid freezing might not always be ideal, as it can result in the formation of larger ice crystals, potentially damaging the food's structure. 4. Food Size: The size and shape of the food item influence the freezing process. Smaller items freeze more quickly and evenly than larger ones. Large items may require longer freezing times or pre-processing techniques such as blanching to ensure proper freezing and preservation of quality.
- 7. CONT………… 5. Insulating Effect: Some packaging materials or food structures may have insulating properties that affect the freezing rate. Understanding and accounting for these effects can help optimize the freezing process and ensure consistent quality across all parts of the food item. 6. Storage Time: The duration for which the food will be stored frozen impacts the freezing process. Longer storage times may require stricter control over freezing conditions to maintain quality, such as minimizing temperature fluctuations and preventing freezer burn.
- 8. EQUIPMENT FOR FREEZING 1. Blast Freezers: Used in commercial food processing to rapidly freeze food products. These freezers circulate cold air at high velocities to reduce the time it takes for food to freeze, preserving texture and quality. Example Foods: Shrimp, scallops, lasagna, pasta dishes. Blast Freezer Image
- 9. Cont.…. 2. Cryogenic Freezers: Utilize extremely low temperatures achieved through the use of liquid nitrogen or carbon dioxide. They are commonly used in industrial settings for freezing food, pharmaceuticals, and biological samples. Example Foods: Ice cream, bakery products, ready-to-eat meals. Cryogenic Freezer Image
- 10. CONT………… 3. Tunnel Freezers: Conveyor belt systems that pass food products through a chilled tunnel, rapidly freezing them. They are commonly used in large-scale food production facilities. Example Foods: Berries, diced vegetables, french fries, shrimp. Tunnel Freezer Image
- 11. Cont.…… 4. Plate Freezers: Utilize flat plates that come into direct contact with the product to freeze it quickly. They are often used in seafood processing to preserve freshness. Example Foods: Fish fillets, whole fish, beef cuts, chicken parts. Plate Freezer Image
- 12. Negative Effects of Freezing On Quality Of Food 1. Texture Changes: Some foods, particularly fruits and vegetables with high water content, may experience texture changes upon freezing and thawing, resulting in a loss of crispness or firmness. 2. Flavor Loss: Freezing can cause flavor loss or changes in taste and aroma, especially in delicate foods or those with volatile compounds. 3. Formation of Ice Crystals: Improper freezing techniques or storage conditions can lead to the formation of large ice crystals, which can damage the cellular structure of food and affect its quality.
- 13. CONT……….. 4. Freezer Burn: Exposure to air and fluctuating temperatures in the freezer can lead to freezer burn, causing dry, discolored patches on the surface of frozen foods and negatively impacting their taste and texture. 5. Limited Storage Life: While freezing extends the shelf life of food, it is not indefinite. Over time, frozen foods can still degrade in quality due to factors such as temperature fluctuations and moisture loss.
- 14. Positive Effects of Freezing On Quality Of Food 1. Preservation of Freshness: Freezing halts the growth of microorganisms, preventing spoilage and extending the shelf life of food products. 2. Nutritional Retention: Freezing can help preserve the nutritional content of foods, including vitamins, minerals, and antioxidants, as it slows down enzymatic activity and oxidation. 3. Convenience: Freezing allows for batch cooking and bulk storage, making it convenient to prepare meals in advance and have them readily available for consumption.
- 15. CONT………… 4. Reduced Food Waste: Freezing enables consumers to store excess perishable foods for longer periods, reducing the likelihood of food being wasted due to spoilage. 5. Seasonal Availability: Freezing allows consumers to enjoy seasonal fruits and vegetables year-round by preserving them when they are in abundance and less expensive.
- 16. CONCLUSION Freezing food plays a crucial role in modern food preservation, offering numerous benefits that contribute to food safety, convenience, and economic efficiency. By reducing the growth of microorganisms and slowing down enzymatic reactions, freezing extends the shelf life of perishable foods, thereby minimizing food waste and allowing consumers to enjoy seasonal produce year-round.
- 17. Cont.…….. Moreover, freezing retains the nutritional quality of foods better than other preservation methods, ensuring that essential vitamins and minerals remain intact. From a practical standpoint, freezing enables bulk purchases, meal preparation in advance, and efficient storage, making it an indispensable technique for households, food manufacturers, and distributors alike.