factors_affecting_growth

factors_affecting_growth - August 28, 2008 Factors...

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August 28, 2008 Harrison FDST 4030/6030 Factors Affecting Microbial Growth and Survival 1 Factors Affecting Microbial Growth and Survival Mark Harrison, Ph.D. FDST 4030/6030 Harrison FDST 4030/6030 Factors Affecting Microbial Growth and Survival { Water content { Environmental temperature { pH { Oxidation-Reduction Potential { Nutrients { Presence or absence of antimicrobials { Other microflora { Processing treatment z e.g., thermal treatment, high pressure, radiation, etc. Harrison FDST 4030/6030 Food Preservation { Low/reduced temperature { High temperature { Antimicrobials (“Preservatives”) { Radiation { Modified atmospheres { Drying { High pressure processing { Pulsed electric fields { Aseptic packaging { Combinations to achieve “Hurdles” Harrison FDST 4030/6030 Factors Affecting Microbial Growth { Intrinsic Parameters - Inherent to plants and animals which can influence microbial activities { Extrinsic parameters { Hurdle Concept/Hurdle Technology Harrison FDST 4030/6030 Hurdles { If relying on single factor to inhibit pathogen growth z Water activity <0.85 z pH <4.6 { If combining factors z pH 5.2 combined with water activity of 0.92 Harrison FDST 4030/6030 Microbial Growth - Four Phases { Lag – z Cells adjust to their new environment { Induce or repress enzyme synthesis and activity { Initiate chromosome and plasmid replication { If they are spores they differentiate into vegetative cells z Time depends on temperature, inoculum size, and physiological state of the organism z Actively growing cells transferred to new environment have shorter lags z Can manipulate the environment to extend lag
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August 28, 2008 Harrison FDST 4030/6030 Factors Affecting Microbial Growth and Survival 2 Harrison FDST 4030/6030 0 2 4 6 8 10 0 1 22 43 64 86 07 2 Hours Log No. "Normal" Extended Lag Harrison FDST 4030/6030 Effect of temperature or pH on lag times of Listeria monocytogenes in the presence of 2% NaCl, a w 0.989 ( USDA PMP ver 5.1) Harrison FDST 4030/6030 Microbial Growth { Exponential (Log) z Bacterial cells reproduce by binary fission { 1 to 2 to 4 to 8 to 16 to 32 to 64 to 128 and so on z Number of organisms at any time directly proportional to initial number of m/o z Temperature effect { Decrease by 10 o C decreases growth rate 2- fold { Time and temperature have great effect on final population Harrison FDST 4030/6030 0 2 4 6 8 10 0 1 2 Hours "Normal" Slowed Log Harrison FDST 4030/6030 0 2 4 6 8 10 0 1 28 49 6 Hours Extended Lag Extended Lag, Slowed growth Harrison FDST 4030/6030 Microbial Growth 6.9-20 Molds, optimal 10-30 Psychrotroph at 5 o C 3.46 Limited conditions 0.3 Optimal conditions Bacteria Doubling time (h) Organism
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August 28, 2008 Harrison FDST 4030/6030 Factors Affecting Microbial Growth and Survival 3 Harrison FDST 4030/6030 Microbial Growth { Stationary { Death Harrison FDST 4030/6030 0 2 4 6 8 10 0 1 22 43 64 86 07 28 49 6 Hours Log No. "Normal" Faster die-off Harrison FDST 4030/6030 Growth Temperature Ranges 15 to 20 12 to 15 -5 to +5 Psychrophiles 30 to 35 25 to 30 -5 to +5 Psychrotrophs 35 to 47 30 to 45 5 to 15 Mesophiles 60 to 90 55 to 75 40 to 45 Thermophiles Maximum Optimum Minimum Temperature ( o C) Harrison FDST 4030/6030 Temperature { Low temperature extremes z Frozen { Primarily restricts growth { Not an effective means to reduce
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factors_affecting_growth - August 28, 2008 Factors...

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