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Thermal Processing Part 2

Thermal Processing Part 2 - Thermal preservation of...

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1. How does one design and verify a heating process for a specific product that is equivalent to at least 2.8 minutes at 121 C ? (i.e. a legal process) Commercial sterilization of low acid foods in hermetically sealed containers Regulation: Minimum equivalency to 2.8 minutes at 121 C (250 F) (12- D process for C. botulinum spores, D 121 = 0.23 min) Thermal preservation of foods (con’t)
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Thermal processing of low acid foods is most commonly done using steam-pressurized vessels (a “retort”) continuous retort batch retort 121 C (250 F)
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Question: If a sealed container of Chunky Chicken Noodle Soup is placed into a retort, which is then heated to 121 C (250 F), how long does that container need to remain in the retort in order to receive a legal thermal process ?
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Need two sets of data : 1. Heating / cooling characteristics (temp vs time) for the product, including container size and material How quickly do the contents heat ? 2. Lethality equivalency achieved by each minute of the heating and cooling stages of the proposed process How quickly do bacteria die at the temperatures experienced by the contents ?
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Determining thermal death rate curves 121 C, 250 F (time = t ) 0 C, 32 F ? instantaneous heating instantaneous cooling Let’s back up : Bacteria in capillary tube plate, count colonies
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Number of surviving cells Time 118 C 115 C 110 C 121 C 125 C D-value of a microorganism: Time (min) for 1-log reduction in viable cells D-values: lower at higher temperatures (faster rate of death) higher at lower temperature (slower rate of death) Thermal Death Rate Curves
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Thermal Death Time Curve: Plot of D-values obtained at various temperatures D-value (min) Temperature (F) Importance: Tells us the rate of death (lethality) at any temperature
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Thermal processing of low acid foods is most commonly done using steam-pressurized vessels (a “retort”) continuous retort batch retort
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