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Glycerol in Freezing media -Reply

Enigl enigl at aol.com
Wed Sep 25 15:38:11 EST 1996

In article <s248f09c.077 at mc.edu>, Snazelle at MC.EDU (Ted Snazelle) writes:

> Supposedly the glycerol prevented ice crystal
>formation which would have disrupted the structure of the

Remember, glycerol is a humectant.  It binds water.  So water is not in a
free moisture state.  The same principle is used in any preservation
through drying: reduction of water activity (aw (i.e.a subscript w)).  The
water remains in a glass-amorphous (plastic) state,  no crystal formation
and is unavailable for use by most cells.  Most cells will not metabolize
and will not grow.  They go into an "extended lag phase" on the microbial
growth curve.  When preserving yeasts and molds,  refrigeration is not
mandatory.   I have not tried this (without refrigeration) on bacteria.

A 1:1 ratio of  glycerol to water should be about 0.85 aw.  This is low
enough to stop most (but not all) bacteria, yeasts and molds.

See this reference later this fall:  	
Enigl, Davin C. and Kent M. Sorrells. In Press, 1996.   Water Activity and
Self-Preserving Formulas.  In: Preservative-Free and Self-Preserving
Cosmetic and Drug Products.  Jon J.  Kabara and Donald S. Orth, Eds.
Marcel Dekker, Inc. New York, NY.  


Davin C. Enigl, MS-MEAS, President-Microbiologist
HACCP Validations-sm  Hazard Analysis and Critical Control Points for the
Food, Cosmetic, Pharmaceutical, and Nutritional Supplement Industry

Voice: (916) 989-8264,  Fax: (916) 989-8205,  Pager: (714) 725-7695
9040 Erle Blunden Way
Fair Oaks, CA 95628
September 25, 1996
12:49 pm

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