1/22/15 Growth, survival and death of microorganisms in foods Fate Possible fate of a microorganism a�er gaining access to a food product Number of cells
Growth
Survival
Storage time
Death
Bacterial growth curve Sta�onary Log
th
Log bacterial concentra�on a
De
Lag Time 1 CFU/ml CFU/ml 1/22/15 1.8E+09 1.6E+09 1.4E+09 1.2E+09 1.0E+09 8.0E+08 6.0E+08 4.0E+08 2.0E+08 0.0E+00 1.8E+09 1.6E+09 1.4E+09 1.2E+09 1.0E+09 8.0E+08 6.0E+08 4.0E+08 2.0E+08 0.0E+00 Scien�fic nota�on Log (base 2) Log (base 10) 0 2 4 6 8 10 12 14 16 18 20 22 24 Time (h) Scien�fic nota�on 0 2 4 6 8 10 12 14 16 18 20 22 24 Time (h) 35.0 Log CFU/ml 30.0 25.0 20.0 15.0 Log (base 2) 10.0 Log (base 10) 5.0 0.0 0 2 4 6 8 10 12 14 16 18 20 22 24 Axis Title 2 1/22/15 Log10 CFU/ml 10.0 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 Log (base 10) 0 2 4 6 8 10 12 14 16 18 20 22 24 Time (h) Studying bacterial growth Log10 CFU/ml 10.0 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 G = Log2 − Log1
7.4 3.8 Log 1 Log 2 G=
7.4 − 3.8
=
0.301
G=
Log2 − Log1
Log2
G=
7.4 − 38
= 11.96 ≈ 12
0.310
GT =
0 2 4 6 8 10 12 14 16 18 Time (h) T
G
GT =
T = 8− 4 = 4
4
= 0.3333h
12
GT = 0.33333× 60 = 20 min
Possible fate of a microorganism a�er gaining access to a food product Number of cells
Growth
Survival
Storage time
Death
3 1/22/15 Factors affec�ng growth and survival of microorganisms in foods Intrinsic Factors   pH   Moisture content   Oxida�on-­‐reduc�on poten�al (Eh)   Nutrient content   An�microbial cons�tuents   Biological structures Extrinsic Factors   Temperature of storage   Time of storage   Gaseous environment   Rela�ve humidity   Background microbiota (antagonism, stress) 4