Hi to all
This is the oldest problem in fish technology and we return to it times and
times again. Somebody said that if you do not have published a paper on fish
quality in a peered journal you can not say that you are really a fish
technologist.
TVB and TMA essays are not reliable as decomposition tests in general, unless
you have the reference values for each specie. For instance the TVB basis of
an anchovy or a sardine just taken out of the water could be higher than the
value of TVB at which cod or hake have been already discarded. There are some
seasonal variations too with after spawmming animals showing high TVB values
very quick (short keeping time) . I know our friend Peter Howgate was working
on a paper puting all this information on TVB together.
The initial reason why some limits (e.g. 30 mg of TVB-N/ 100 g of sample in
the case of cod and cod like fish) exist in Europe is because they were
correlated in some way to the production of non-volatile biogenic amines
(like putrescine, cadaverine and spermine) that are of more concern to public
health than volatile amines and that are (or were) more difficult to measure
than TVB-N. Therefore TVB-N is not an absolute indicator of spoilage in
itself, but an indirect indicator of the formation of non-volatile amines in
fish (*).
However, by chance TVB-N could tell us something about fish quality, provided
we have the correlation, for a specific specie, between TVB-N and sensory
quality (before it starts to indicate the possibility of non-volatile
biogenic amines in the fish). But this is a completely different story.
Correlations of that type never were good correlations.
Therefore if we would like to have a refined measure of fish spoilage it
would be possible, along this line, to measure non-volatile biogenic amines.
Again we would need values according to the specie as reference. At
difference of TVB non-volatile amines may (eventually) have an "absolute"
yes/ not value (linked to public health problems starting with allergia). In
this sense putrescine has been indicated by some authors as a promising
indicator (Poli et al, 2000)(**). But this may open the Pandora box because
we risk to transform sharply a fish quality problem in a fish safety problem;
something that nobody really wants.
An alternative way to measure fish "spoilage" is to resort to the Japanese K
value (a ratio based on ATP catabolites content ocurring in the muscle after
death); the K value is an indication of early changes in fish muscle. From
the point of view of the consumer the K value is perhaps the most convenient,
particularly when referring to high priced fish species, because you do not
want to pay for old (even if still edible) fish. Personally, as consumer, I
would prefer the K value in the case of lobsters, shrimp and crab.
Of course it is possible to resort to more modern instrumental methods: "
Intangible but not intractable: the prediction of fish 'quality' variables
using dielectric spectroscopy" Mike Kent et al 2007 Meas. Sci. Technol. 18
1029-1037 (many thanks to the authors that allowed me to cite a 2007 paper
on this subject!)
After saying all that I agree with all that expressed that sensory
assessments are the best and less expensive thing to do the job. I agree with
Klaus with all the limitations he puts regarding sensory assessment in
plants, but, in practice there is little possibility to do ordinary sensory
analysis outside fish plants. Perhaps some of the problems he rightly
mentions could be solved by performing, particularly in the case of doubt
(sensory analysis of raw fish), sensory analysis of cooked samples (tight
wraped in Al foil). Keep your nose near the sample when you open it, and if
there is something wrong definitely you will notice it. In addition the fish
can be tested, and this means that aspects like texture and rancidity changes
could be ascertained too.
Kind regards
Hector M. Lupin
FAO Consultant
(*) Do not ask me for the reference to this. I learned it from late Dr.
Kietzman (Chief Fish Inspector in Hamburg, Germany) , about 35 years ago,
when I was in W. Germany as fellowship student. I got a copy of the
reference paper (from a German journal of the years 20-30, that unfortunately
I lost during one of my movings).
(**) Biosensors applied to biochemical fish quality indicators in
refrigerated and frozen sea bass reared in aerated or hyperoxic conditions.
Poli B.M.; Zampacavallo G.; Parisi G.; Poli A.; Mascini M. Aquaculture
International <http://www.ingentaconnect.com/content/klu/aqui> , Volume 8,
Number 4, 2000, pp. 335-348(14)
-----Original Message-----
From: owner-seafood@ucdavis.edu [mailto:owner-seafood@ucdavis.edu] On
Behalf Of Barbara Blakistone
Sent: 30 March 2007 02:31
To: Surefish Bellingham; Klaus Schallie; Purnendu Vasavada
Cc: seafood@ucdavis.edu
Subject: RE: Decomposition test
I recently spent some time trying to find a quick test for indole. I
did a lot of asking, and no one knew of such a rapid test.
Barbara Blakistone
National Fisheries Institute
-----Original Message-----
From: owner-seafood@ucdavis.edu [mailto:owner-seafood@ucdavis.edu] On
Behalf Of Surefish Bellingham
Sent: Thursday, March 29, 2007 7:35 PM
To: Klaus Schallie; 'Purnendu Vasavada'
Cc: seafood@ucdavis.edu
Subject: RE: Decomposition test
Thanks to all for your input.
I don't know where the crab is being processed. I think what the
client was asking was what to test for if sending samples to an independent
lab for confirm or dispute an FDA detention and also, how to detect decomp in
addition to sensory.
My reply was if sending to an independent lab, test for indole.
According to some given advice, an indole result of 25 to 50 micrograms/gram
would indicate class 2 decomposition and greater than 50 micrograms indicates
class 3.
Regarding a device for rapid detection, I hear there are some in
development, but they need calibration by sensory, and may be expensive and
not convenient.
Any comments regarding any of the above, still welcome.
Thanks!,
Mark
----- Original Message -----
From: Klaus Schallie <mailto:schallie1@shaw.ca>
To: 'Surefish Bellingham' <mailto:Surefish@az.com> ;
'Purnendu Vasavada' <mailto:purnendu.c.vasavada@uwrf.edu>
Cc: seafood@ucdavis.edu
Sent: Thursday, March 29, 2007 4:04 PM
Subject: [Norton AntiSpam] RE: Decomposition test
Hi to all. While I'm a believer in sensory evaluation by
trained analysts and did that for much of my career, doing sensory on a
production line can be very challenging. Proper sensory evaluation should be
done in a controlled environment where air quality, air movement, light and
temperature won't interfere with the assessment.
In a processing plant the air is often saturated with the
odours of all of the product(s) in the area which leads to habituation /
desensitization in the people doing the assessment. Odours from machinery,
steam, detergents, sanitizers, exhaust from internal combustion motors, less
than optimal lighting, lots of noise and all the commotion associated with
the processing operation are additional distractions that may make the job
more difficult if present. While it might be possible to identify very
decomposed product under those situations, less decomposed and borderline
quality could easily escape detection.
Since the original question originated in Bellingham, I'm
guessing the product might be dungeness crabs. Without knowing the exact
circumstances, processing only live crabs would largely eliminate the risk of
processing decomposed product.
Klaus Schallié
18192 Claytonwood Crescent
Surrey, BC Canada V3S 8G8
Tel. (604) 576-1879
e-mail schallie1@shaw.ca <mailto:schallie1@shaw.ca>
This archive was generated by hypermail 2b29 : Fri Mar 30 2007 - 08:01:59 PDT