TVB-N for salmonDear Kate
EU Commission Decision 95/149/EC lays down maximum TVB contents of certain species or families of fish above which the fish is considered unfit for consumption. Note that these limits apply to unprocessed fish. The limit for Salmo salar is 35mgN/100g of flesh. Note that this is the only species of salmon specified in the Decision. The Decision gives the preferred procedure for determining TVB, but other procedures, including the microdiffusion method are permitted. I suppose the requests for statements of TVB contents by buyers in the EU stem from this regulation. The regulation actually states: "Unprocessed fishery products ... shall be regarded as unfit for human consumption where, organoleptic assessment having raised doubts as to their freshness, chemical checks reveal that the following TVB-N limits are exceeded:" In other words TVB measurements should not be used as the first test of freshness, but only where the sensory, (not organoleptic), evaluation is not clear-cut.
TVB is a very poor indicator of freshness of any species of fish and I am not aware of the experimental basis of using TVB at any level as an indicator of fitness of salmon for consumption. In my opinion if the sensory evaluation is equivocal about the fitness for consumption it must be spoiled and a responsible quality assurance programme would reject it. Don't forget, regulatory bodies are concerned with fitness for consumption, not with commercial quality which is a matter for seller and buyer. However it does not matter whether or not the regulatory limit has any experimental or quality basis the regulations require that salmon must meet the requirements. The pH of Salmo salar is quite low and I would expect growth of TMA-producing bacteria, (increase in TVB during storage is due to production of TMA), to be slow and I would expect increase in TVB to be very slow. My guess is more than 20 days in ice before TVB approaches the limit. You could always use the microdiffusion procedure which will give you about 8 units lower than the official procedure to be sure of meeting the requirements of the Decision.
I am not aware of any information on effect of canning on TVB in salmon, but heat processing decomposes TMAO to produce TMA and DMA so I would expect canning to increase TVB content of salmon.
Peter Howgate
----- Original Message -----
From: Kate Abraham
To: List serv (E-mail)
Sent: Friday, February 11, 2005 4:14 PM
Subject: TVB-N for salmon
The request for TVB-N analysis as a freshness indicator has re-surfaced with some buyers in the EU with regard to raw salmon, prior to canning. Other than personal opinions does anyone have any references regarding (a) the unreliability (and impracticality) of testing fresh salmon and (b) the invalidity of testing canned salmon.
Many thanks
Kate Abraham
Quality Assurance Manager,
Canadian Fishing Company.
email kate.abraham@canfisco.com
Tel: (604) 443 0231
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