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thermal processing is specifically designed to:
- make the product safe and shelf-stable
- reduce the number of microorganisms of public health concern to a statistically small level (bot-cook)
- suppress the growth and activity of spoilage microorganisms
what must one first understand to successfully apply thermal processing?
microbial thermal destruction kinetics
what is the general form of the order of reaction for a single component?
what is the zero order of the order of reaction equation?
what is the first order of the order of reaction equation?
what is the second order of the order of reaction equation?
for thermal destruction of microbes, enzymes, and nutrients generally follow which order reaction rate?
first order reaction rate
what is the D value?
- the decimal reduction time
- heating time at any given temperature which results in 90% destruction of the microbial population, or one decimal reduction in the surviving population
how is the D value obtained from the graph?
the time required for the curve to pass one log cycle
what is the thermal death time?
- time in minutes required to destroy a microbial population at any given temperature
- used exclusively in process calculations
what does death time depend on?
what is the slope of the TDT line?
what does z represent mathematically?
the negative reciprocal slope of TDT or D value curve
what is the sterilization reference temp?
250°F or 121°C
what is the pasteurization reference temp?
- 150°F or 180°F
- (wtf does that mean??)
how is the TDT tube method done?
- small glass tubes are flame sealed with small samples
- heated for various times at constant temp
- either survivors are counted, or tubes are tested for positive or negative
what are the advantages of the tube method?
- simple and inexpensive
- growth can be observed in a tube
- easy subculturing
- heating lags are minimized if tubes are very small
what is the TDT can method?
- use special TDT cans (D=208, H=0.006)
- mechanical closures
- small steam retorts
- these can be used for both cans and tubes
- heating and cooling performed in a special "mini retort"
what are the advantages of the TDT can method?
- processing conditions simulate commercial operations
- spoilage by gas formers readily detected by can swelling
- faster and easier sealing than TDT tubes
what are the disadvantages of the TDT can method?
- heating and cooling lag compensation needed
- need special retort
- subculturing more difficult than with tube
- post processing contamination due to leaks
what is the TDT thermoresistometer method?
- three chambers (sample introduction, heating, subculturing)
- carriers transfer samples
- steam controlled temperature
- precise time (0.001min)
- small sample size (1/100mL)
- no lag
- six replicates and statistical approach
- most probable number of survivors
what are the advantages of the thermoresistometer method?
- no lag
- instantaneous heating and cooling
- short times possible (6 sec with less than 0.5% error)
- high temp
- automatic subculturing
- less labor
- operation is simple
what are the disadvantages of the thermoresistometer method?
- high cost
- direct inoculation not possible
what is MPN?
most probable number - per given unit (per mL, per container, etc)
how is MPN calculated?
- where a=amount of sample (per can or per mL)
- n=total number of replicates
- q=number of negative samples
what is the MPN technique based on?
- statistical approach
- makes use of logarithmic order of death
- can be used for both initial count and final counts
- used in Stumbo's thermoresistor approach for D (accurate and sophisticated technique)
means F at reference temp T (250°F) is 0.2min (Fo) and z value = 18°F