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SCI 305 PRESERVATIVES

Purpose of preservatives

An ideal preservative
• Have a broad spectrum activity against all
microorganisms
• Be effective in low concentrations
• Be colorless and odorless
• Not react with the other ingredients
• Be more soluble in water than in oil
• Not be affected by temperature changes
• Not alter its activity due to changes in pH
• Be safe at all concentrations
• Have a low cost
...


• To be effective, a preservative agent must be dissolved in
sufficient concentration in the aqueous phase of a
preparation
...

• Acidic preservatives like benzoic, boric, and sorbic acids are
more undissociated and thus more effective as the medium
is made more acid
...


• Thus, it is meaningless to suggest preservative effectiveness
at specific concentrations unless the pH of the system is
mentioned and the undissociated concentration of the
agent is calculated or otherwise determined
...

• It is essential for the compounding formulator to examine
all formulative ingredients as one affects the other to
ensure that each agent is free to do its job
...


• In the product development process, the lowest
effective concentration of an antimicrobial
preservative that is demonstrated to be effective
by an antimicrobial preservative effectiveness
test should be used
...


Mode of action
• Preservatives interfere with microbial growth,
multiplication, and metabolism through one or more of
the following mechanisms:
– Modification of cell membrane permeability and leakage
of cell constituents (partial lysis): Lysis and cytoplasmic
leakage
– Irreversible coagulation of cytoplasmic constituents (e
...
,
protein precipitation)
– Inhibition of cellular metabolism, such as by interfering
with enzyme systems or inhibition of cell wall synthesis
– Oxidation of cellular constituents
– Hydrolysis

Phenols

• Butylated hydroxyanisole (BHA) and the
related compound butylated hydroxytoluene
(BHT) are phenolic compounds that are often
added to foods to preserve fats
...

• Oxygen reacts preferentially with BHA or BHT
rather than oxidizing fats or oils, thereby
protecting them from spoilage
...

• Incompatible with ferric salts
...

• Effective by decomposing to reform
formaldehyde in small quantities
...

• Popular with manufacturers due to their low
cost and effectiveness
...
2% released forlmaldehyde
• “Contains formaldehyde” must be in label if
>0
...

This preservative has activity against gram-positive and
gram-negative bacteria, including Pseudomonas
aeruginosa
...

• Heterocyclic compounds
...

• Also used in cooling-water systems and paper mill-water
systems
...

– a powerful cytotoxin
• Growing concern over the use of isothiazolinones because of
sensitization and allergic reactions
...

• Esters of p-hydroxybenzoic acid
...


• Typically, more than one paraben is used in a product
– Use of mixtures allows use of lower levels while increasing
preservative activity

• Often used in combination with other types of preservatives to
provide preservation against a broad range of microorganisms
...
1-0
...
0
...


ethylhexylglycerin
• Introduced in 1992
– Alternative to parabens

• the multifunctional molecule
–
–
–
–

Mild preservative
Antii-microbial stabilizer
Humecant
Emmolient

• Deodorant active
– Inhibits growth and multiplication of odour-causing Gram positive
bacteria

• Lotions, shampoos, conditioners



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