Subtopic: Kinetics of microbial death – pasteurization and sterilization of milk and other liquid foods
Question Statement:
Milk sterilization kinetics is based on inactivation of index microorganism, Bacillus stearothermophilus. The D-values at 121.1°C and 139.1°C are 1.2 min and 0.019 min, respectively. For 12 log-cycle reduction of this microorganism at 130°C, the processing time in second is ______
Official Answer Key:
110 to 112
Step-by-Step Solution & Explanation
The thermal-resistance (z-value) is found from the two D-values using the standard thermal death-time relation: z = (T2−T1)/log₁₀(D1/D2) = (139.1−121.1)/log₁₀(1.2/0.019) = 18/log₁₀(63.16) = 18/1.8004 = 10.0°C. D-value at 130°C: D_130 = D1×10^[−(130−121.1)/z] = 1.2×10^(−8.9/10) = 1.2×0.1288 = 0.1545 min. For 12 decimal (log-cycle) reductions, processing time = 12×D_130 = 12×0.1545 = 1.8541 min = 1.8541×60 = 111.3 s, within the accepted band 110–112.
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