Factors Affecting Growth and Survival in Foods

Factors Affecting Growth and Survival in Foods - Factors...

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Factors Affecting Microbial Growth and Survival Harrison FDST 4030/6030 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 High pressure Genetic damage – radiation damage Activities of other microflora 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 Harrison FDST 4030/6030 Hurdles – Hurdle Concept If relying on single factor to inhibit pathogen growth Water activity <0.85 pH <4.6 If combining factors pH 5.2 combined with water activity of 0.92 Harrison FDST 4030/6030 Microbial Growth - Four Phases Lag – 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 Time depends on temperature, inoculum size, and physiological state of the organism Actively growing cells transferred to new environment have shorter lags Can manipulate the environment to extend lag
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Factors Affecting Microbial Growth and Survival Harrison FDST 4030/6030 2 Harrison FDST 4030/6030 0 1 2 3 4 5 6 7 8 9 0 1 22 43 64 86 07 2 Log No. Hours "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) Bacterial cells reproduce by binary fission 1 to 2 to 4 to 8 to 16 to 32 to 64 to 128 and so on Number of organisms at any time directly proportional to initial number of m/o 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 "Normal" Faster die-off Harrison FDST 4030/6030 Microbial Growth Organism Doubling time (h) Bacteria Optimal conditions 0.3 Limited conditions 3.46 Psychrotroph at 5 o C 10-30 Molds, optimal 6.9-20
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Factors Affecting Microbial Growth and Survival Harrison FDST 4030/6030 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.
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This note was uploaded on 09/30/2011 for the course FDST 4030 taught by Professor Harrison during the Fall '11 term at University of Georgia Athens.

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Factors Affecting Growth and Survival in Foods - Factors...

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