U of S | Mailing List Archive | alt-photo-process-l | Re: gum preservatves

Re: gum preservatves

Suitable choice of preservative depends on many factors, such
as whether you want to protect from gram negative bacteria,
gram positive bacteria, fungi, etc., as well as the storage
condition, particularly the pH. Sodium benzoate is an
effective bactericide in acidic material (such as soda
beverages) but not so effective for materials that are only
modestly acidic or not acidic at all.


A good general purpose biocide with a broad range of
protection is 2-phenylphenol (for alkaline pH) and methyl
paraben (mildly acidic to neutral pH), thymol,
p-chloro-m-cresol, and isothiazolones. Benzoic acid (benzoate)
has more narrow spectrum of effect and usage, although it may
work ok if you use it at such a high level as 1%.

Generally speaking, biocide with carboxyl groups (such as
benzoic acid, parabens, etc.) are effective in the pH range
where the carboxyl group is undissociated. This limits their
useful pH range to the acidic side of the corresponding pKa.

Biocide like 2-phenylphenol or p-chloro-m-cresol would be
still very effective at 0.1% of the solid material in the

Incidentally, I recall that this is probably 2nd or 3rd or 4th
time this topic came up, and I've also posted all these and
probably some more info in the past.

Ryuji Suzuki
"Strange how people who suffer together have stronger connections
than people who are most content." (Bob Dylan, Brownsville Girl, 1986)