ANTIMICROBIAL AGENTS Powerpoint
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 ?
CFR listings for anti-microbial agents
172.177 Sodium nitrite used in processing smoked chub.
172.175 Sodium nitrite.
172.170 Sodium nitrate.
172.165 Quaternary ammonium chloride combination.
172.160 Potassium nitrate.
172.155 Natamycin (pimaricin).
172.130 Dehydroacetic acid.
184.1021 Benzoic acid
184.1005 Acetic acid.
184.1061 Lactic acid.
184.1081 Propionic acid.
184.1221 Calcium proplonate.
184.1490 Methylparaben.
184.1563 Ozone.
182.3739 Sodium bisulfite.
182.3766 Sodium metabisulfite.
182.3795 Sodium sorbate.
182.3798 Sodium sulfite.
182.3862 Sulfur dioxide
182.3089 Sorbic acid.
182.3225 Calcium sorbate.
182.3616 Potassium bisulfite.
182.3637 Potassium metabisulfite.
182.3640 Potassium sorbate.
184.1670 Propylparaben.
184.1754 Sodium diacetate.
184.1784 Sodium propionate.
173.300 Chlorine dioxide.
Factors Affecting Microbial Growth
pH
Oxygen tension
Temperature
Nutrients
FACTORS AFFECTING THE SELECTION OF ANTIMICROBIAL AGENTS
pH of the food product
Food composition
Processing, and storage conditions
Solubility
Flavor
Cost
Marketing impact
PRINCIPLES FOR USING ANTIMICROBIAL AGENTS
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.
EFFECTIVE pH RANGE OF COMMON ANTIMICROBIAL AGENTS
| Agent | pH Range |
| Benzoic acid | 2.5-4.0 |
| Sorbic acid | 3.0-6.5 |
| Proplonic 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 |
SORBIC ACID
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.
BENZOIC AC1D
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
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.
PROPIONIC ACID
pKa = 4.87
Usage limited to 0.1%.
Effective against molds, but no effect an yeast.
Major usage in broad and baked goods.
Calcium salt most used form.
184.1081 Propionic acid.
184.1221 Calcium proplonate.
184.1784 Sodium propionate.
SU L F I T E S
pKa = 1.89 7.0
Effective against molds, yeast, bacteria. Yeast more resistant than lactics.
Major usage in wines. Used often for Its antibrowning and color stabilization characteristics.
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.
NITRITE
pKa = 3.29
Effective against C. botuHnum.
Used in cured meat products.
Reacts with myoglobin to give cured meat color.
172.177 Sodium nitrite used in processing smoked chub.
172.175 Sodium nitrite.
172.170 Sodium nitrate.
172.160 Potassium nitrate
PARABEN -
pKa = 8.47
Usage level limited to 0.1%.
Effective against yeast and molds, gram+ bacteria.
Longer chain esters are more effective. Heptyl > Propyl > Ethyl > Methyl.
Usage In U.S. Is not great as demonstrated by food labels. Found In artificial sweeteners, baked goods, a few salad dressings, beer?.
Inappropriate Uses of Antimicrobial Agents
Addition to dried products
Addition to heat sterilized products
Addition to cover-up poor sanitation
Addition to foods with the wrong pH
| Antimicrobial Agent | Dissociation Constant | pKa | %
Undissociated at pH 4.5 |
| Sulfur dioxide | 1.54 x 10-2 | 1.81 | 0.2 |
| Acetic acid | 1.76 x 10-5 | 4.75 | 64 |
| Benzoic acid | 6.46 x 10-5 | 4.18 | 13 |
| Propionic acid | 1.32 x 10-5 | 4.88 | 71 |
| Sorbic acid | 1.73 x 10-5 | 4.76 | 65 |
HENDERSON-HASSELBACH EQ.
pH=pKa + log([RCOO-]/[RCOOH])
pH=pKa + log([Ionized form]/[un-ionized form])
pH = pKa + log ([uneffective form]/[effective form])
pH - pKa = log ([uneffective form]/[effective form])
When pH = pKa then pH - pKa = 0.
The log of 1 = 0, thus [uneffective form]/[effective form] = 1
This means that 50% is in the affective form (when the pH = pKa).
When pH - pKa = 1 then [U]/[A]=10 or 9.09% is effective.
When pH - pKa = 2 then [U]/[A]=100 or 0.99% is effective.
This should demonstrate that antimicrobial agents are not effective at pH's above their pKa's.
AMA's become more effective below their pKa's.
If pH -pKa = -1 (or the pH is below the pKa by 1 unit) then 90.9% is effective.
My "Nickle Rules" are:
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 1 unit greater than the pKa, only about 10% is in the effective form.
4. When the pH is one unit less than the pKa, then about 90% is in the effective form.
pH -pKa |
log [U]/[E] |
[Uneffective]/[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 |
|||
-2.00 |
-2.00 |
0.01 |
99.01 |
Distribution coefficient = [ Organic phase] /[ Aqueous phase]
=concentration of the component in the organic phase divided by the concentraion in the aqueous phase
| 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 |