Gita
I can go some way in answering your queries.
The natural form of free phosphate in muscle, fish or shrimp, is as the
orthophosphate ion PO4. I write 'free' because there are many other
compounds which contain phosphate in a combined form. The usual analytical
procedure measures total orthophosphate after digestion of the, that free
and combined. It is usual in food studies to present the data as
phosphorous, P, or as orthophosphate, PO4. Expressing it as P2O5 is more
commonly used for soils and minerals. Textbooks of food analysis will
describe procedures for measuring phosphate.
The material used for treating shrimp or fish to promote water retention is
a condensed phosphate made by heating orthophosphate. This cause phosphate
units to combine to form polyphosphates. The material sold as
'polyphosphate' is predominately the trimer, tripolyphosphate, and sometimes
this trimer is available as tripolyphosphate and is often used for dipping
shrimp. It is possible to separate the polymers in a mixture of so in
principle it should be possible to analyse an extract of shrimp muscle to
detect tripolyphosphate to confirm if the product had been treated with a
polyphosphate. However, polyphosphates are hydrolysed by enzymes in muscle
to orthophosphate so the interpretation of any analyses for polyphosphates
might be negative even in treated products.
Certainly any product that has been treated with polyphosphate will have a
higher phosphate content by analysis than one that has not been treated, but
the problem in enforcement is in setting a maximum level above which you are
sure the product has been treated. The phosphate content of shrimp varies
naturally so the questionable product has to be well above the average
phosphate content for the untreated product before any action can be taken.
A similar situation prevails with regard to water content. Soaking shrimp in
polyphosphate solution will increase water content and analysis of water
content should indicate in the product has been so treated. But again the
water content has to be above the normal range before action can be taken.
For example, assume shrimp with a water content of 80% is treated so that
there is a 10% increase in weight, that is 100g of shrimp has absorbed 10g
of water. The resulting water content will be 81.8% and I think this will be
within the normal range of water contents in shrimp. If you think you have a
problem with over use of polyphosphate to increase weight, you will have to
come to a process control agreement with your supplier. You could monitor
incoming material on a regular basis for phosphate and water contents and
any unusual increase in either, or especially both together should be noted
and perhaps queried with you supplier.
There are papers on this subject in the research literature, but as you hint
copies of these are not free - the typical charge for reprints in the range
30-40 USD - but some extension agencies provide leaflets on the subject. One
is available at the oneFish site, Polyphosphates in Fish Processing TAN 31,
URL http://www.fao.org/wairdocs/tan/x5909e/x5909e00.htm
Following is a reference, including the abstract which will give you a
flavour of a typical article.
Peter Howgate
------------------------------------
Vickie Tenhet, Gunnar Finne, Ranzell Nickelson, Don Toloday (1981).
Phosphorous levels in peeled and deveined shrimp treated with sodium
tripolyphosphate. Journal of Food Science, vol. 46, pp350-352.
ABSTRACT
Using volumetric and spectrophotometric methods for the determination of
phosphorous, untreated shrimp were shown to have high and variable
phosphorous content. When peeled and deveined shrimp were treated with 0.5%
and 1.0% sodium tripolyphosphate (STP) solutions, the STP uptake was shown
to be low. At these low treatment concentrations the phosphorous content in
the treated shrimp did not exceed the range of natural phosphorous found in
untreated shrimp. When higher treatment concentrations were used, treated
shrimp could be identified. The stability of STP in treated shrimp during
frozen storage was investigated using a P32 STP isotope. After 2 wk of
frozen storage at -26°C only 12% of the total activity could be attributed
to STP. At the same time, pyrophosphate was present at a level of 25% and
orthophosphate at 27%. During further frozen storage, the STP concentration
remained at approximately 12%, pyrophosphate dropped down to as low as 2%
while orthophosphate gradually increased reaching 45% of total activity at
the end of 10 wk storage period.
----- Original Message -----
From: "Gita Narasati" <gita.n.k@gmail.com>
To: "seafood" <seafood@ucdavis.edu>
Sent: Tuesday, December 11, 2007 2:30 AM
Subject: Phosphate in shrimp
> Dear friends,
>
> My client would like to find information regarding phosphate in shrimp or
> prawns.
>
> Is there any standard or free scientific journals I can have access to in
> regards to the type of natural phosphate (P2O5) within shrimp and the
> method
> for testing phosphate-treated shrimp?
>
> Based on my knowledge that checking phosphate-treated shrimp is not by
> testing the phosphate, instead by testing the moisture content. Is this
> correct? What I want to know is there any official/scientific references
> for
> this matter?
>
> Thank you.
>
> Best regards,
> Gita
>
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