Paul Lehman (palehman@yahoo.com)
Fri, 04 Jun 1999 06:26:31 -0700 (PDT)
Thanks to all who have provided insights on the Bloom rating issue.
My original questions came about from some recent experimentation on
the carbon process. Specifically, Knox gelatin worked fine but a
generic grocery brand of gelatin proved to be only half as sensitive.
Certainly there may be multiple differences between the two products
but Bloom rating may be a factor to consider.
Let me stumble through my interpretation of the information as I
understand it so far.
Wayde Allen provided a nice short definition of Bloom rating. But his
information also provides me with some additional confusion. He said:
--- Wayde Allen <wallen@boulder.nist.gov> wrote:
> The bloom rating is a measure of the rigidity of the
> gelatin. Basically,
> 7.5 g of gelatin is mixed with 105 ml of distilled
> water in a "bloom
> bottle".
>snip...
He then added:
> One interesting note from the Ward, Courts book
> (page 509) is that "Bloom
> strength is approximately proportional to the square
> of the solution
> concentration."
On the surface this seems contradictory. If a 7% concentration of one
gelatin gives a bloom rating of X, and a 7% concentration of another
gelatin gives a bloom rating of Y, how can the bloom rating be
proportional to the concentration if the solutions were prepared at the
same concentration?
One possibility is that bloom rating may actually be a function of the
molarity of the solution rather than the concentration. In other words,
a 7% concentration (by weight) of one gelatin may contain more or less
the number of molecules of protein than another gelatin with a
different bloom rating (this assumes that non-protein impurities that
may be present do not affect the bloom rating) (or could the bloom
rating be a function of impurity content?). Thus the bloom rating may
only be an indicater of water content of the dried granules (similar to
hydrated salts).
If it is not molarity, then there must be a molecular difference
between gelatins with different bloom ratings.
(We may also have to draw a distinction between gelatin being "hard"
when in the gel state, and being "hard" in the dry state, meaning
requiring a high temperature to cause disolution).
My 2nd question:
> and Is gelatin sensitivity to dichromates a
> function of the bloom
> rating?
If I have read the responses correctly, it appears that this issue has
not been specificly addressed in a controlled study (although it may be
in the deep literature somewhere). However, to be able to classify
gelatins by there mechanical hardness there must be a chemical
difference as well (again, assuming that impurities do not play a
role). The hardness of a gel is a function of water content, the
molecular structure of the protein to hold the water, and the probable
propencity for hydrogen bonding. If this is true, the bloom rating must
be indicating a molecular difference in the gelatin protein, either
longer or shorter chain lengths, the shape of the protein (coiled or
straight), or in the number of functional groups (amines, hydroxyls,
etc) present or exposed on the surface of the protein molecule.
So, my guess is that dichromate sensitivity may be a function of Bloom
rating. Those factors that may influence bloom rating should also
influence dichromate cross-linking of the gelatin (gelatine size, shape
and availability of functional groups). However, the degree of
sensitivity corrilation to the bloom rating is the final question.
What we (I) need to answer this properly is 1) a real smart protein
biochemist who knows how proteins interact under these conditions, and
2) a good controlled study to test the relationhsip between dichromate
sensitivity and bloom rating. Neither of which are currently available
to me at this time.
I guess I'll just stick to Knox gelatin for now.
Thanks again.
Paul A. Lehman
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