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ChillingRefrigeration

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ChillingRefrigeration

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    1. Chilling/Refrigeration FDT 3305, Principles of Food Engineering Pawan S. Takhar Animal and Food Sciences Texas Tech University

    2. Chilling equipment

    3. Alternative Classification Based upon the rate of movement of ice front Slow Freezers 0.2 cm/hr - Still air and cold stores Quick Freezers 0.5-3 cm/hr - Air blast and plate freezers Rapid Freezers 5-10 cm/hr - Fluidized bed freezers Ultra rapid Freezers 10-100 cm/hr - Cryogenic freezers

    4. Slow Freezers: Still Air and Cold Stores Food is frozen in air circulating with natural convection. Air temp -20 to -30 C. Freezing Rate 3-72 hrs. (Low heat transfer coefficient). Fans are used in cold stores to increase heat transfer coefficient. Cold stores are used to store foods, meat, to harden ice cream frozen by other methods

    5. Quick Freezer Blast type, Plate Air is circulated at -20 to -40 C at 1.5-1.6 m/s

    6. Batch Freezer

    7. Double Contact Plate Freezer

    8. Rapid Freezer: Fluidized Bed Food is contained on a perforated tray or conveyer belt. Air between -25 to -35 C is passed at high velocity (2-6 m/s) Each food comes in contact with air individually

    9. Ultra rapid: Direct Contact Liquid Nitrogen Tunnel Freezer

    10. Cryogenic

    11. What is chilling? A unit operation in which temperature of a food is reduced between -1 and 8 C.

    12. Effect of temperature Biochemical changes caused by micro-organisms and naturally occurring enzymes increase with temperature. Therefore, by reducing temperature we reduce the biochemical changes.

    13. Why we chill foods? To reduce the rate of biochemical activity (respiratory rate of foods) To reduce the rate of microbial activity To preserve sensory and nutritional value of foods Consumers consider chilled foods as convenient, easy to prepare, high quality, healthy natural and fresh

    14. First order Kinetics A+B=C+D [A]=Concentration of A k is reaction constant, given by Arrhenius equation: A is a constant, Ea is activation energy, R is universal gas constant

    15. Categories of refrigerated foods based upon storage temperature -1 to +1 C (Fresh meats, sausages and ground meats, smoked meats and breaded fish) 0 to +5 C (Pasteurized canned meat, milk, cream, yoghurt, prepared salads, sandwiches, baked goods, fresh pasta, fresh soups and sauces, pizzas, pastries and unbaked dough 0 to +8 C (fully cooked meats, fish pies, cooked or uncooked cured meats, butter, margarine, hard cheese, cooked rice, fruit juices and soft fruits

    16. Effect of respiration rate Refrigeration system should be designed so that respiration heat of foods is removed. Therefore, it is important to know Refrigeration Heat of foods Whether the food is climacteric or non-climacteric

    17. Climacteric Foods Climacteric foods show a burst of ethylene production when they ripen Their rate of respiration increases near the point of optimum ripeness These foods ripen after harvesting They soften and become sweeter during storage Examples: apple, apricot, avocado, banana, mango, peach, pear, plum, tomato

    18. Non-Climacteric Foods Non climacteric foods do not show a burst in ethylene production when they ripen They do not show increase in respiration rate These foods ripen before harvest These foods do not undergo many changes during storage Examples: cherry, cucumber, fig, grape, grapefruit, lemon, pineapple and strawberry

    19. Heat of respiration (Watts/tonne) 0 C 10 C 15.5 C Apples 10-12 41-61 58-87 Bananas 73-82 65-116 - Oranges 9-12 35-40 68 Carrots 46 93 - Potatoes - 20-30 -

    20. Chilling Injury Chilling injury causes undesirable physiological changes (external or internal browning, skin blemishes, failure to ripen) Fruits and vegetables undergoing chilling injury should be stored above a certain temperature Chilling injury results from imbalance of metabolic activity There is an overproduction of some toxic metabolites

    21. Examples of foods undergoing chilling injury Apples (<2-3 C) Bananas (< 12-13 C) Lemons (< 14 C) Mangoes (<10-13 C) Melons, pineapples, tomatoes (< 7-10 C)

    22. Effect on Meats In slaughtered animals oxygen supply stops and aerobic respiration declines. During anaerobic respiration glycogen is converted into lactic acid and pH of the meat decreases. Rigor mortis starts. Cooling during anaerobic respiration produces desirable texture and color and reduces bacterial contamination. Do not cool meat before rigor mortis has occurred otherwise cold shortening may occur.

    23. Cold Shortening Extremely tough meat (meat is inedible). Darker meat color.

    24. Heat Shortening of Meats Heat shortening occurs when chilling is not sufficiently fast. Meat becomes pale and tough

    25. Abbattoir Diagram

    26. Rate of refrigeration It is important to control the rate of refrigeration for meats

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