D and Z values in Thermal Processing of Foods

Table 1: Heat Resistance of Bacteria Important to Thermally Processed Foods^[1]
Class of Food	Type of Microorganism	Microorganism(s)	Reference Temperature (°F)	D-Value (minutes)	Z-Value (°F)
Low-acid food (pH > 4.6)	Thermophiles^a (spores)	Flat-sour group (B. stearothermophilus)	250	4.0 – 5.0	14-22
	Mesophiles^b (spores)	Putrefactive anaerobes (C. botulinum types A and B)	250	0.10 – 0.20	14-18
	Mesophiles^b (spores)	C. sporogenes group (including P.A. 3679)	250	0.10 – 1.5	14-18
Acid food and acidified food (pH 4.0 – 4.6)	Thermophiles (spores)	B. coagulans (facultatively mesophilic^c)	250	0.01 – 0.07	14-18
	Mesophiles (spores)	B. polymyxa and B. macerans	212	0.10 – 0.50	12-16
		Butyric anaerobes (C. pasteurianum)	212	0.10 – 0.50	12-16
		B. licheniformis	200	4.5	27
Acid food and acidified food (pH < 4.0)	Yeasts, molds, and mesophilic non-spore-bearing bacteria	Lactobacillus species, Leuconostoc species	150	0.50 – 1.00	8-10

^aA thermophilic microorganism is one that thrives at a relatively high temperature, such as 50 °C or above.

^bA mesophilic microorganism is one that thrives at a moderate temperature, such as 37 °C.

^cA facultative microorganism is one that can live under more than one set of environmental conditions.

^[1]Adapted from Table 7 of FDA's Thermally Processed Foods of Draft Guidance for Industry: Acidified Foods. Accessed 10th May 2015.

Table 2: Thermal Process Lethalities for Acidified Foods^[2]
Finished Equilibrium pH	Thermal Process Lethality^*
3.1 – 3.2	F10/195 = 0.1 min
3.3 – 3.5	F10/195 = 1.0 min
3.5 – 4.0	F10/195 = 16-23 min
4.0 – 4.2	F15/200 = 5.0 min
4.3 – 4.4	F15/200 = 23 min
4.3 – 4.4	F15/200 = 10 min
4.3 – 4.4	F15/212 = 10 min
4.5 – 4.6	F15/212 = 23 min
4.5 – 4.6	F18/230 = 23 min

^*Expressed as Fz/Ref, where F is the destruction time in minutes, z (^oF) is the increase in temperature that results in a 90 percent reduction in the D-value, and Ref is the reference temperature (^oF).

^[2]Adapted from Table 8 of FDA's Thermally Processed Foods of Draft Guidance for Industry: Acidified Foods. Accessed 10th May 2015.

Table 3: Thermal death times (i.e. D-values) of various microbes
Microbe	D-value, min	Ref. Temp, ^oC	Conditions	Reference
Clostridium botulinum A16037 spores	0.4	115.6	Tomato Juice pH=4.2 z-value = 9.4^oC	[Ref 1]
	1.6	110
	6	104.4
	1.3	115.6	Phosphate Buffer pH=7.0 z-value = 9.9^oC
	4.4	110
	17.6	104.4
Campylobacter jejuni	1	55	Unknown	[Ref 2]
Salmonella spp	0.98	60
Listeria monocytogenes	3.3/60	71.7
Escherichia coli	1/60	71.7
Staphylococcus aureus	4.1/60	71.7
Clostridium perfringens	145	90
Clostridium botulinum	12/60	121.1
Bacillus stearothermophillus	5.0	121.1

[Ref 1]:Appl Environ Microbiol. 1977 July; 34(1): 23 - 29
[Ref 2]:Thermal Sterilisation Notes
[Ref 3]:Resources
[Ref 4]:Resources
[Ref 5]:Resources