Process Effects on Microbiological
Contaminant Levels

Phares O. Okelo, Ph.D.
Center for Veterinary Medicine/FDA

AFSS Public Meeting
May 22, 2007

Slide 2

Outline

Ingredient/feed manufacturing processes

Process effects on contaminant levels

Some examples

Slide 3

Ingredients and Manufacturing Processes (swine diet)

Slide 4

Ingredient/Feed Manufacturing Process Categories

Thermal
Physical
Chemical
Other

Slide 5

Ingredient-Contaminant-Process Interactions

Manufacturing Process

Ingredient

Contaminant

Slide 6

Ingredient-Contaminant-Process Interactions ‘cont.

Slide 7

Microbiological Contaminants

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Manufacturing Processes - Thermal

(Temp, time, moisture)

• Spray-drying
• Drum/tube-drying
• Fluid-bed drying
• Pelleting

Slide 9

Manufacturing Processes – Thermal
(spray-dried animal blood cells)

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Manufacturing Processes - Physical

(psd, temp, press, time)

• Grinding
• Pressing
• Centrifugation
• Membrane separation
• Mixing

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Manufacturing Processes - Chemical

(aw, time, pH, temp, conc)

• Preservatives
• Anti-microbial activity
• Fermentation

Slide 12

Manufacturing Technologies and Inactivation Kinetics

N = Noe-kt
Where:
N = number of viable bacterial cells after t seconds
No = number of bacterial cells at the start of thermal process
t = duration of thermal process, s
k = activation constant of the organism (death rate), dimensionless

Slide 13

Manufacturing Technologies and Inactivation Kinetics (DT value)

DT value

The time (min) required to kill 90% of viable vegetative cells or spores at T (oC)

DT (min)

No 0.1No

T oC

Slide 14

Manufacturing Technologies and
Inactivation Kinetics (DT value ‘cont.)

DT = [2.303/exp(ln ko – Ea / RT)]
where:
ko = the pre-exponential factor, dimensionless
Ea = activation energy of the organism, (J mol-1)
R = the universal gas constant, (8.314 J mol-1 K-1)
T = absolute temperature of thermal process, K

Slide 15

Manufacturing Technologies and
Inactivation Kinetics ‘cont.

N = Noe-(ln ko–Ea/RT)t
Where:
N = # of viable bacterial cells after t seconds
No = # of bacterial cells at start of thermal process
ko = the pre-exponential factor, dimensionless
Ea = activation energy of the organism, (J mol-1)
R = the universal gas constant, (8.314 J mol-1 K-1)
T = absolute temperature of thermal process, K
t = duration of thermal process, s

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Manufacturing Processes – Thermal
(spray-dried animal blood cells)

Slide 17

Inactivation of M. avium – (spray-dried animal blood cells)

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Manufacturing Technologies and Inactivation Kinetics (HHP)

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Expert Opinion – Microbes (process effects)

If the microbiological contaminant is present in the
specified feed ingredient, will the processing step in
question 1) increase, 2) reduce, or 3) have no effect
on the level of the microbiological contaminant?

(Please restrict your estimates to effects occurring only during the specific
processing step.)

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Expert Opinion – Microbes (magnitude of effect)

What is the estimated magnitude, in terms of
percentages, of that effect (e.g., 50% reduction,
200% increase, etc.)?

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Expert Opinion – Microbes (expert’s certainty on estimate)

How certain are you in your estimation? Please
use the following scale:
 

• 1 = very uncertain (just a guess)
• 2 = uncertain
• 3 = medium certainty
• 4 = fairly certain
• 5 = very certain (I know what I am talking about!)

Slide 22

Microbes Inactivation (Expert Opinion Table)

Slide 23

Manufacturing Processes - Thermal

(Temp, time, etc)

• Spray-drying (~45-55 oC, few min)
• Drum/tube-drying (~35-40, few min)
• Fluid-bed drying (~35-40, few min)
• Pelleting (~66-100 oC, 30-140+ seconds)

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Post Processing Operations (Effects on Level of Microbes)

• Storage
• Transportation

• Feeding Practices

  Criteria for estimation of effects of these operations on the levels of microbes
  in ingredients and feed is being developed.

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Final Level of Microbes in Feed

The overall estimate of levels of microbes in the feed will be based on
the following factors:

• Initial levels in ingredients
• Composition of contributing ingredient in diet (%)
• Processing effects
• Daily consumption

Slide 26

Microbe Inactivation - Levels After Processing (M. avium)

Slide 26

Microbe Inactivation - Levels After Processing (M. avium)

Slide 27

Expert Opinion Worksheet Microbiological Contaminant

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Summary

• Start with diet with known ingredients & composition,
• a list of list of identified microbiological contaminants
• Assess effects of key manufacturing processes on contaminant levels
  using established techniques (and available data on: process parameters,
  microbe levels, expert opinion, etc.)
• Use model to estimate final contaminant levels in mixed feed

Slide 30

Questions ?