Wayde Allen (wallen@boulder.nist.gov)
Wed, 03 Nov 1999 09:32:10 -0700 (MST)
On Tue, 2 Nov 1999 FotoDave@aol.com wrote:
> Why do you think so?
>
> I think it protects not because I think the harderner has some anti-organism
> function or because the gelatin will become really hard but for the simple
> fact that it is harder to swell the gelatin, which means less ability to
> absorb water, and insects or microorganism loves the moist area especially
> moist food.
Gelatin is really nothing more than animal connective tissue (collagen)
that has been treated with either an acid or alkali solution and heated so
that the protein helix of the collagen separates. This denaturization of
the collagen molecule is basically irreversible, but the molecules still
have their binding sites that allow them to cross link between each other
when they get close enough. This is what gives you the gel nature of the
gelatin. If you add enough water to keep the molecules separated you get
a liquid. If you add heat to increase the energy enough that the bonds
that form can't become permanent you get a liquid. The gel phase is when
the moisture content and energy levels get sufficiently low that a
majority of the molecules can get close enough to begin cross-linking.
A hardening solution only serves to modify the cross links so that it
would take more energy to break them once formed.
Can a hardening agent protect the gelatin from insects and
microorganisms? I suppose that there could be some toxicity of a
chemically modified gelatin cross-link, but aside from that possibility
the hardened gelatin is really not as tightly bound together as the
original animal connective tissue from which it came. I've never known
animal tissue to be impervious from attack by insects or microorganisms.
I'd say that the only issue would be moisture content. I think I'd agree
with your claim that the hardened film might absorb less water from the
air.
> > And this brings up another question of mine, namely does this so-called
> > hardening actually increase abrasion resistance or does it merely serve to
> > strengthen the crosslinking in the wet gel making the wet film a bit
> > tougher and less water soluble?
>
> They are the same thing, isn't it?
Not exactly. The gel is in a state with partial cross linking. That is
why it is a bit rubbery. Adding a little bit more energy or water can
cause some of the existing cross links to break while others are trying to
form. A hardening agent at this stage can help to pin some of the bonds
down so that they can't separate. This would toughen the wet film.
The dry, or shall we more accurately say solid, gelatin film has reached
its state of maximum cross linking. Adding hardener at this stage isn't
really going to increase the number of cross links. I'm guessing that the
number of cross links formed is the primary feature describing the hardness
of the gelatin film. A hardener would increase the energy required to
break these bonds and yes could make these bonds even tougher, but I
wonder about how much the hardening agents we are using actually affect
this?
> You know there isn't such a thing as dry gelatin.
Sure, but I think you would agree that it exists in solid, gelatinous, and
liquid phases.
- Wayde
(wallen@boulder.nist.gov)
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