Lecture_3___milk_pasteurization__1_

Lecture_3___milk_pasteurization__1_ - Lecture 3:...

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1 Lecture 3: Pasteurization of Fluid Milk Carmen I. Moraru Cornell University Milk pasteurization Pasteurization: the heat treatment that ensures destruction of the vegetative forms of microorganisms Objectives: ¾ Ensuring product safety: Destroy pathogenic and potentially pathogenic bacteria ¾ Keeping product quality Destroy spoilage bacteria and enzymes
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2 Pathogens in milk ¾ Mycobacterium tuberculosis ¾ Coxiella burnetii ¾ Salmonella ¾ Listeria monocytogenes ¾ Yersinia enterocolitica ¾ Campylobacter jejuni ¾ Staphylococcus aureus ¾ Escherichia coli 0157: H7 Inactivation of microflora ¾ Depends on: ¾ Type of microorganism ¾ Initial level of contamination ¾ Acidity of milk ¾ Temperature-time regime ¾ The extent of the pasteurization treatment is determined by the heat resistance of the most heat-resistant enzyme or microorganism. ¾ Traditionally, milk pasteurization regimes were based on the destruction of Mycobacterium tuberculosis and Coxiella burnetii. ¾ With the recognition of new pathogens, the time-temperature regimes are continuously examined.
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3 Review: thermal destruction of microorganisms ¾ In thermal processes, the rate of destruction of microorganisms is generally accepted to follow first order kinetics: log [N / N 0 ] = -t / D where: N = microbial population at time t N 0 = initial microbial population D = decimal reduction time, or time required for a 1-log cycle reduction in the microbial population. ¾ D is a measure of the heat resistance of a microorganism. Ex: D 72 ° C = 1 min. at means that for each minute of processing at 72 ° C the microbial population will be reduced by 90%. Thermal destruction of microorganisms – contd. Temperature coefficients ¾ The influence of temperature on microbial inactivation rates is expressed using the thermal resistance constant (z-value): log [D / D R ] = -(T - T R ) / z z(T) = the temperature increase needed to accomplish 1-log reduction in D. D R = the magnitude of the decimal reduction time at a reference temperature (T R ) Microorganisms with higher resistance to temperature change have larger z(T).
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4 Typical values for thermal coefficients Z (°C) D 121°C (min) Bacteria 5-10
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This note was uploaded on 05/02/2009 for the course FDSC 4250 taught by Professor Moraru during the Spring '09 term at Cornell University (Engineering School).

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Lecture_3___milk_pasteurization__1_ - Lecture 3:...

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