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Low Temperature Microbial Growth Control

Refrigeration. Limiting microbial growth through reduction in rates of chemical, biochemical, and microbial kineticsHolding food in the temperature range of -l to 8 oC. CONTROL OF MICROBIAL GROWTH DURING REFRIGERATED STORAGE. Low temperatures slow the rate of each step in the microbial growth cycl

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Low Temperature Microbial Growth Control

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    1. Low Temperature Microbial Growth Control

    2. Refrigeration Limiting microbial growth through reduction in rates of chemical, biochemical, and microbial kinetics Holding food in the temperature range of -l to 8 oC

    3. CONTROL OF MICROBIAL GROWTH DURING REFRIGERATED STORAGE Low temperatures slow the rate of each step in the microbial growth cycle, resulting in longer lag phase, slower growth in the exponential phase, and reducing the generation time Some pathogens can grow at low temperatures (Clostridium botulinum type E at 5.5?; Listeria moncytogenes at 3?)

    6. External Factors Influencing Growth of Microorganisms Initial Microorganism Population. Characteristics of the Food Effects Of Processing.

    7. Initial Microorganism Population The type and number of microorganisms present during refrigerated storage is important in determining shelf life in refrigerated foods. In general, more microbes present initially results in decreased storage life.

    8. Characteristics of the Food Factors influencing shelf life of refrigerated foods Water activity pH nutrient content for microbial growth preservative content Low pH, low water activity, and proper formulation can lengthen refrigerated storage time of foods.

    9. Effects Of Processing Temperature Pretreatment (i.e., pasteurization) pH adjustment Drying (reducing water activity) Addition of preservatives Storage atmosphere. Refrigerated storage is focused on spoilage bacteria, however pathogens may be present.

    14. Freezing The freezing process is the removal of thermal energy from the food product to the extent required to reduce the temperature below the freezing temperature of water. The thermal energy removed as a part of freezing is primarily latent heat of fusion required to convert water to ice within the product

    15. Food Freezing Food freezing is the preservation process that depends on the reduction of product temperature to levels well below the temperature at which ice crystals begin to form within the food. By reducing the temperature of the product to -10 to -20?, the normal reactions that cause deterioration of foods are reduced to negligible or minimal rates.

    17. Definition of Freezing Time time required to reduce the product temperature from the initial freezing temperature to a temperature of 5 degrees below the initial freezing temperature

    18. Effect of Freezing Rate on Product Quality The formation of large ice crystals causes greater damage to the product structure and negative impact on the quality attributes of that product. As might be anticipated, more rapid freezing and formation of small ice crystals usually result in a more desirable product after freezing and frozen--food storage

    19. INDIRECT CONTACT FREEZING SYSTEMS Plate freezing system Indirect-contact freezing system Cabinet freezing system Scraped surface, continuous system

    21. DIRECT-CONTACT FREEZING SYSTEMS Air blat system Continuous spiral conveyor system Continuous fluidized bed system Continuous immersion freezing system Continuous cryogenic freezing systems

    23. Individual Quick Freezing (IQF) The concept of IQF involves exposure of individual pieces of the product to a low temp. medium for a relatively short period of time. In some situations, the rate of freezing is increased by promoting more intimate contact between the product pieces and the cold refrigerant. In other situations, IQF is achieved by using very low temperature cryogenic refrigerants as a freezing medium.

    24. STORAGE OF FROZEN FOODS The quality of a frozen-food is influenced by storage conditions. The changes in quality decrease as temperature is decreased, maintaining low storage temperatures increases the cost of frozen-food storage. Higher temperatures in frozen-food storage must be avoided due to the sensitivity of the frozen-food to temperature. Experience has established that a frozen-food storage temperature of -18? is accepted as a safe storage temperature for extended shelf life of a frozen food.

    28. Changes in quality Microbial activity (negligible at –18C) Biochemical reaction Enzymatic reaction (blanching for vegetables, sulfur dioxide/ reduction of oxygen/ addition of acid for fruits)

    29. FREEZE DRYING Moisture is removed from the solid state (ice) directly to the vapor state by sublimation. Drying actually occurs in two steps, primary and secondary drying stages. It is in the primary stage that water is removed by sublimation, whereas vaporization of unfrozen liquid water molecules occurs in the secondary stage of drying.

    30. Product quality of Freeze Drying The original structure of the food is maintained and flavor retention in is excellent. The cost of freeze drying is very high.

    31. Steps in Freeze Drying Freezing. Primary Drying. Secondary Drying. Heat and Mass Transfer in Freeze Drying

    33. END

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