Answers to each part are in BOLD The following data were obtained from a thermal
ID: 65658 • Letter: A
Question
Answers to each part are in BOLD
The following data were obtained from a thermal resistance experiment conducted on a spore suspension at 113oC. Determine the DT value of the microorganism (4 min).
Time (min)
Number of spore survivors
0
106
4
1.05 x 105
8
1.08 x 104
12
1.03 x 103
) For the same spore suspension, a set of DT was measured at different temperatures, as shown below. Determine the thermal resistance of the spore, z value in oC (11oC).
Temperature (°C)
D (minutes)
104
27.5
107
14.5
110
7.5
113
4.0
116
2.2
3-c) A sterilizer is used to obtain a 12-log reduction of the same spore in a juice product with an initial load of 5.7 x 108 spores per mL of product. How long would it take to achieve the 12 log reduction at the following temperature: a) 116 °C and b) 121oC; c) what is the final concentration of spores per liter? d) what is F0? (26.4 min; 9.3 min; 0.57/L; 9.3 min)
Time (min)
Number of spore survivors
0
106
4
1.05 x 105
8
1.08 x 104
12
1.03 x 103
Explanation / Answer
1. DT= The time required, at the temperature of T °C in moist-heat conditions, to reduce the number of microorganisms of a given species to 10% (1 logarithmic reduction).
So the answer is 4oC
2. The z-value is defined as the temperature coefficient of microbial destruction, i.e. as the number of degrees of temperature which causes a 10-fold variation of D
The answer is 110oC
3. F0 is the equivalent exposure time at 121.11°C of the actual exposure time at a variable temperature, calculated for an ideal microorganism with a temperature coefficient of destruction equal to 10 °C.
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