We have measured TVBN in king/chinook salmon (Oncorhynchus tshawytscha) by the microdiffusion method and found minimal changes during storage at 0°C. In air packs, there were no significant changes from the base level of 8.9 mg/100g over 18 days and in MAP packs levels were below 11 mg/100g during storage of up to 54 days.
Fletcher, G.C.; Summers, G.; Corrigan, V.; Cumarasamy, S.; Dufour, J.-P. 2002: Spoilage of king salmon (Oncorhynchus tshawytscha) fillets stored under different atmospheres. Journal of Food Science 67: 2362-2374.
In collaboration with Food Science Australia we have also recently carried out some yet to be published analyses looking at the effect of high pressure processing on both king and Atlantic (Salmo salar) salmon. Again, during 24 days' storage at 0°C in vacuum packs, TVBN levels only increased from initial levels of 11.6 and 12.5 to maximum mean levels of 15.2 and 14.7 mg/100g in king and Atlantic salmon respectively. This was despite some samples being obviously spoilt according to sensory evaluation. TVBN is a very poor indicator of spoilage in salmon and I doubt that even canning spoilt fish would ever get the levels above the regulatory limit.
Graham C Fletcher
Senior Research Scientist,
Seafood Research Unit,
Crop & Food Research, Private Bag 92169
Auckland, New Zealand
Physical Address:
Mt Albert Research Centre
120 Mt Albert Road, Mt Albert, Auckland
Phone: 64-9-845 9012
Fax: 64-9-845 9029
Email: FletcherG@crop.cri.nz
Website: www.crop.cri.nz
>>> "P Howgate" <phowgate@clara.co.uk> 12/02/2005 8:51 a.m. >>>
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 ab
out 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
>>> <Ron.Tume@foodscience.afisc.csiro.au> 10/02/2005 7:39 p.m. >>>
Hi Graham
I am fairly sure Sieh is on holiday in Vietnam for Chinese New Year. I will get gack to you asap.
Thanks, Ron
-----Original Message-----
From: Graham Fletcher [mailto:FletcherG@crop.cri.nz]
Sent: Thu 10/02/2005 1:11 PM
To: Tume, Ron (FSA, Cannon Hill); Ng, Sieh (FSA, Werribee)
Cc:
Subject: Hi Sieh & Ron
Hi Sieh & Ron
I now have all our data for the HPP salmon shelf-life trial and want
to analyse it before sending it out. However, I don't have the colour
data for the day 1 samples nor the pathogen data for the final sampling
day.
Can you send these to me Sieh or do you have the Minolta data Ron? I
recall that there were problems with the instrument so it may not have
been recorded electronically but may be on the paper printouts. We also
had a breakdown with our Minolta and missed most of the day 23 king
samples.
Did anything happen about the flora identification from day 1? Joseph
is doing the final flora id now.
Cheers
Graham
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