AntiMicrobial Agents Keep these questions in mind

1
Anti-Microbial Agents Keep these questions in
mind

• Why and when do we need them?
• What limits their use?
• What are the principles governing their usage?
• What choices do we have? what types of food have
  antimicrobial agents in them?
• What foods are inappropriate for using
  antimicrobial agents? what other additives can be
  used to preserve foods and avoid the
  "preservatives", label?
• Why do preservatives work some times and fail at
  other times ?
• Why are processing changes important to the
  effectiveness of antimicrobial agents ?

2
Anti-Microbial Agents(Code of Federal Regulation
sections)

• CFR Sections
• 170
• 172
• 182
• 184
• Standards of Identity
• 101.22 Labeling

3
Anti-Microbial Agents (AMA)

• Generally Bacteriostatic rather the bacteriocidal
• Consist of both acid the non-acid types
• Acidic AMAs most common

4
FACTORS AFFECTING THE SELECTION OF ACIDIC
ANTIMICROBIAL AGENTS

• Antimicrobial activity against different
  organisms
• Microbial load in product
• pKa of the AMA
• pH of the food product
• Food composition
• Processing, and storage conditions
• Solubility
• Flavor
• Cost
• Marketing impact

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Principles for Using AMAs

• Most agents are weak acids.
• Most work when in the un-ionized form.
• Most are not effective above their pKa's.
• Most affect flavor.
• Most are affected by processing, order of
  addition distribution between oil and aqueous
  phase

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Modified Henderson-Hasselbach

• pH pKa log ( ineffective form / effective
  form )
• pH pKa log ( ionized form / unionized form
  )
• pH - pKa log ( ineffective form / effective
  form )
• pH - pKa log ( ionized form / unionized form
  )
• If pH is greater (Higher) than pKa, more of the
  acid is going to be in the ineffective form.
  NOTE this is a log relationship so a little
  change can mean a lot.

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How much is effective?

• When pH pKa then pH - pKa 0.
• The log of 1 0, thus ineffective
  form/effective form 1
• This means that 50 is in the effective form
  (when the pH pKa).
• When pH - pKa 1 then U/A10 or 9.09 is
  effective.
• When pH - pKa 2 then U/A100 or 0.99 is
  effective.

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pH vs Effectiveness

• pH -pKa log U/E Ineffective/Effective
  Effective
• 2.00 2.00 100 0.99
• 1.88 1.88 75 1.32
• 1.70 1.70 50 1.96
• 1.40 1.40 25 3.85
• 1.00 1.00 10 9.09
• 0.70 0.70 5 16.67
• 0.40  0.40 2.5 28.57
• 0.00 0.00 1 50.00
• -0.30 -0.30 0.5 66.67
• -0.40 -0.40 0.4 71.43
• -1.00 -1.00 0.1 90.91
• -1.40 -1.40 0.04 96.15
• -1.70 -1.70 0.02 98.04
• -1.88 -1.88 0.01 98.68

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Quiz

• If I have an antimicrobial agent with a pKa of 4
  and add this to a food having a pH of 4, how much
  do I need to add to achieve an effective
  concentration of 0.1?

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Answer

• 1 - What percent of the AMA is effective?
• pHpKa so ? percent is effective
• 50
• If we need 0.1 then we need 2X that much
• 0.2 X 50 effective 0.1
• Know of any potential problems?

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Gradys Nickel Rules

• 1. AMA are only used at or below pH's to their
  pKa's.
• 2. At pH pKa, only 50 of the AMA will be
  effective.
• 3. When the pH is one unit less than the pKa,
  then about 90 is in the effective form.
• 4. When the pH is 1 unit greater than the pKa,
  only about 10 is in the effective form. Forget
  about it!

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Distribution Coefficient

• Distribution coefficient
• Organic phase / Aqueous phase
• concentration of the component in the organic
  phase divided by the concentration in the aqueous
  phase
• How does this impact antimicrobial agents?

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Distribution Coefficients

• Compound Distribution Coefficient
• Propionic acid 0.17
• Sorbic acid 3.0
• Benzoic acid 6.1
• p-hydroxybenzoic acid methyl ester 5.8
• p-hydroxybenzoic acid ethyl ester 26
• p-hydroxybenzoic acid propyl ester 87.5
• Which is most water soluble? Most fat soluble?

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Distribution Coefficient

• Does it matter? Why?
• Where do the bugs grow?
• What is the effect of process?
• What is the effect of order of addition?
• What is the effect on kill?
• What is the effect on order of use?

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Most Common AMAs

• Agent pH Range
• Benzoic acid 2.5-4.0
• Sorbic acid 3.0-6.5
• Propionic acid 2.5-5.0
• Acetic acid 3.0-5.0
• Parabens 3.0-9.0
• Sulfites 2.5-5.0
• Nitrites 4.0-5.5

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Sorbic Acid, Sorbate, Potassium Sorbate

• pKa 4.8
• Usage level limited to 0.1.
•  
• Broad spectrum against yeast and molds. Lactic
  acid bacteria at low pH.
• Major usage In salad dressings, fruit juices,
  cottage cheese.
• Potassium salt Is the most widely used form.
• 182.3640 Potassium sorbate.
• 182.3795 Sodium sorbate.
• 182.3089 Sorbic acid.

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Benzoic Acid, Benzoate, Sodium Benzoate

• pKa 4.2
• Usage level limited to less than 0.1 by
  regulation.
• Most active against yeast and molds.
• Major uses In beverages, juices, non-standard
  "Jellies". margarine.
• Acid form relatively Insoluble and not used much.
• 184.1021 Benzoic acid
• 184.1733 Sodium benzoate

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Acetic Acid

• pKa 4.76
• Usage level limited by taste.
• More effective against yeast and bacteria.
• Major usage In "Pickled" foods. Also In "natural"
  breads.
• Sodium diacetate used In some breads.
• 184.1754 Sodium diacetate.
• Preservative labeling may not be required

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Propionic acid, Propionate, Calcium Propionate

• pKa 4.87
• Usage limited to 0.1.
• Effective against molds, but no effect on yeast.
• Major usage In bread and baked goods.
• Why?
• Calcium salt most used form.
• 184.1081 Propionic acid.
• 184.1221 Calcium propionate.
• 184.1784 Sodium propionate

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Sulfite, Sulfur Dioxide, Metabisulfite

• pKa 1.89, 7.0
• Effective against molds, yeast, bacteria.
• Yeast are more resistant than lactics.
• Major usage In wines.
• Used often for Its antibrowning and color
  stabilization characteristics. Most common use -
  remember to think about water
• Flavor problems, hypersensitivity.
• 182.3739 Sodium bisulfite.
• 182.3766 Sodium metabisulfite.
• 182.3798 Sodium sulfite.
• 182.3862 Sulfur dioxide
• 182.3616 Potassium bisulfite.
• 182.3637 Potassium metabisulfite.

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Nitrite

• Effective against C. botulinum.
• Used In cured meat products.
• Reacts with myoglobin to give cured meat color
• Nitrate is not an anti-microbial agent unless it
  is converted to nitrite
• 172.177 Sodium nitrite used in processing smoked
  chub.
• 172.175 Sodium nitrite.
• 172.170 Sodium nitrate.
• 172.160 Potassium nitrate

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Parabens, Methyl, Propyl, Heptyl

• pKa 8.47
• Usage level limited to 0.1.
• Effective against yeast and molds, gram
  bacteria.
• Longer chain esters are more effective. Heptyl gt
  Propyl gt Ethyl gt Methyl.
• Usage In U.S. Is not great as demonstrated by
  food labels. Found In artificial sweeteners,
  baked goods, a few salad dressings, beer?.
• 172.145 Heptylparaben.
• 184.1490 Methylparaben.
• 184.1670 Propylparaben.

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Other AMAs

• 172.165 Quaternary ammonium chloride combination.
• 172.130 Dehydroacetic acid.
• 184.1061 Lactic acid.
• 172.133 Dimethyl dicarbonate.
• 184.1538 Nisin preparation. 172.155 Natamycin
  (pimaricin).
• 172.155 Natamycin (pimaricin).
• 184.1563 Ozone.
• 173.300 Chlorine dioxide.
• Lactoferrin application to meat carcasses SA
  GRAS 2002
• Lysozyme GRAS
• Lactoperoxidase - GRAS

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Gradys AMA Nickel Rules

• First, measure the pH
• Remember AMAs are only hurdles
• No amount of AMA can defeat bad sanitation
• You may be able to use fermented products that,
  through no fault of their own, happen to contain
  antimicrobial agents

25
Anti-Microbial Agents

• Why and when do we need them?
• What limits their use?
• What are the principles governing their usage?
• What choices do we have? what types of food have
  antimicrobial agents in them?
• What foods are inappropriate for using
  antimicrobial agents? what other additives can be
  used to preserve foods and avoid the
  "preservatives", label?
• Why do preservatives work some times and fail at
  other times ?
• Why are processing changes important to the
  effectiveness of antimicrobial agents ?