Unit Operations: Food Safety Kinetics

5-7D Process

Meat cooking is this common process time

Factors Influence D-Value

Microorganism type or strain Composition Physico-chemical parameters of the medium -Aw and pH Age of the cells or state of growth Temperature D= Do 10^((To -T)/z))

7D Process

Milk pasteurization is this common process time microbe: Coxiella burnetti

D121

Minute for chemical changes -Non-enzymatic browning (0.4-40) -Denaturation of proteins (5) -Destruction of Thiamine (38-380) -Chlorophyll destruction (14-350) -Enzyme inactivation (1-10)

Example of TDT

Reduce 10^9 to 10^-3 is 12D Time in minutes to completely kill population

Heat Resistant Spores

in the can, 5x12 is about 60 minutes Want to make sure the can is free from spoilage Design the can based off of the spoilage microbe

Combined Approach

k=2.303/D

F Value Delievered

By a process as a result of time temperature history experienced by the product during the process Must be integrated math. Look at F value divide into small segments, and calc F value Process calculation by general method

Z(C) for Certain Reactions

C. bot 8-12 C. sporogenes 9-13 Nonenzymatic browning 17-39 Denaturation of Proteins 5-10 Destruction of Thiamine 20-30 Chlorophyll destruction 38-80 Enzyme inactivation (in general) 8

12D Process

Canning is this common process time (industrial practice) 121C Clostridium Botulinum

60 Minutes

Canning process is about this amount of time

Bacillus subtilis

D135= 9 minutes

Escherichia coli

D55= 4 minutes

Listeria Monocytogenes

D60= 5.0-8.3 minutes

Common Process Timings

Depending on type of food

Fo

F value calculated using z of 18 and reference D250 are often designated as D250= 1.16 minutes Desired log reduction 6 F= 1.16 * 6= 7 minutes

F Value Specified

For a process and it is determined from the log cycle reduction by considering safety and wholesomeness of the professed product Time required to achieve reduction at given temp Log a= 6 Log b= 10 6-1=5 5 About 5 minute processing time Amount time for process to achieve certain log reduction

Increase in Temperature kills Microbes Readily

How does D value change with Temperature? D value will significantly decrease

Spoilage Probability

Knowledge on target lethality, decimal reduction time and microbial population can help determine this Assume n1 and n2 are initial and final microbes per container and r is total number of containers

F Value

Sterilizing value, equivalent minutes at the reference temperature -Time required to achieve stated reduction at a given temperature -A measure of heat treatment or sterilization process F=Dt(log a - log b) F= sterilizing value (min) at a given temperature DT- D value of a microbe at specified temperature a and b- initial and final number of viable spores

D Value is Influenced by Composition

Substrate: Cream style corn Organism: PA3679 D250: 2.47 Substrate: Whole-kernel corn Organism: PA3679 D250: 1.52 Substrate: Phosphate buffer Organism: PA3679 D250: 1.31 Make sure used in appropriate conditions

Reference Temperatures

T= 250F is often used as this Zz= 18F is common for used for thermal processes Some can be changed Use 250 or 121 for canning

Temperature Dependence of Rate Reactions

The activated complex theory for chemcial reactions is the basis for Arhenius equation k= ko E^ -Ea/RT

Why Short Processing Time at Higher Temperatures are Preferred for Quality Retention?

The microbes will be more sensitive to temperature change and can be destroyed faster, to better retain the quality, the nutrition of the bacteria is better at higher temps

Kinetic Approach

d ln N/ dt= -k

Microbiological Approach

d log N/ dt= -1/D

why short processing time at higher temperatures are preferred for quality retention?

-The d value increase will become shorter and shorter 50C dvalue at 10 70C dvalue at 1 min 130C .1second Target microbe -interested in retention, numbers are not correct 50C d= 10 min 70C d= 9.1 min 90C d= 8 min -Minimal impact on organisms

Ea

= 2.303 R T^2/ z Math relationship

B. megaterium

D100= 10 minutes

A. niger

D100= 5-10 minutes

Clostridium sporogenes

D121= 0.15-2.6 minutes

Bacillus stearothermophilus

D121= 4.0-5.0 minutes

Clostridium botulinum

D125= 0.1-0.3 minutes

Log 1 Reduction

10 fold, 90% change 10,000 (10^4) final number of micro left in food

Log 3 Reduction

10* 10* 10= 1,000 fold 99.9% change 100 (10^2) final number of micro left in food

Log 5 Reduction

10*10*10*10*10= 100,000 fold 99.999% 1 final number left of micro left in food

Log 4 Reduction

10*10*10*10= 10,000 fold 99.99% change 10 final number left of micro left in food

Log 2 reduction

10*10= 100 fold 99% change 1,000 (10^3) final number of micro left in food

Z Value

A negative reciprocal slope of the thermal resistance curve (log D vs temperature) A temperature range which results in a 10 fold change in D values Always reported positive though the slope is negative -Important to specify temperature scale (C or F) = T2-T1/ log D1- log D2 ex) 10.0C or 18.0 F

Assumptions

All the population have same resistance (or) homogeneous population There is no clumping No heat activation (for spore germinations) No injury Uniform process treatment (in nutritious medium) Variability and homogeneous, deviation needs to be considered, no clumping Some can be clumped together and 2 colonies can be counted as one, so just assuming no clumping Lethal environment is uniform

From Survivor Curve Equation

An infinite time will be required for the destruction of all viable microbes Calc. never going to get 0 in processed foods in these conditions

Thermal Destruction of Bacteria

Bacteria have a logarithmic order of death when heat processed Log of viable bacteria concentration vs time of exposure is a straight line relationship called survivor or a thermal destruction curve

Decimal Reduction Time (D-Value)

The time required to reduce the microbial population by 90% Varies for each microorganism and temperature -Unites: minute Larger D-values correspond to more: Resistant microbes -Dependent on temperature -How much time it takes to reduce population by 90%

Thermal Death Time (TDT)

Time in minutes required to completely destroy microbial population at any given temperature -Depends on the initial population (d value is not function of initial population) -Higher the population, longer is the TDT -Depends on the sensitivity of testing method -Used widely in thermal processing -TDT curve will be similar to D-value curve; TDT=nD

Spores

Tref= 250F or 121C

Vegetative Organism

Tref= 80 or 60C with z value of 6 to 9C

60C

Usually Pasteurization