Dear Steve
Many issues here. Let's start with the question ' .. are there frozen
seafood products that will retain better quality at -35ºC than at -29ºC'.
(Why restrict the question to seafoods, don't freshwater products matter?).
As far an I am aware any fish product will retain a particular, (not
'better' as frozen storage will not make quality better), level of quality
for longer at -35ºC that at -29ºC. The quantitative data on effect of
temperature on rates of deterioration of frozen fish is not very large and
not of good quality, but my best estimate of the doubling temperature, that
is the change in temperature that will double, or halve, the rate of
deterioration is 6ºC. Lowering storage temperature from -29ºC to -35ºC then
will double the storage life.
This is relative given some criterion of quality, or change in quality; are
there particular products that will benefit from this extension? You have
answered that question already - oily fish. These are very susceptible to
the development of rancid flavours arising from oxidation of lipids.
Packaging that excludes air - heavy water glazing is the typical technology
for bulk products - will slow down oxidation, but lowering of temperature
additionally has a marked influence. The recommendations of fish technology
laboratories in Europe is to store frozen fish at -30ºC, and generally this
recommendation is followed in the fish processing industry and in public
cold stores in Europe. Typically in Europe and Scandinavia, seasonally
caught pelagic fish such as herring and mackerel are frozen in solid
water-filled blocks and stored at -30ºC. This enables good quality products
to be available for at least a year. An expert assessor would be able to
detect traces of rancidity at this time, but the intensity would probably
not be of commercial significance. It is possible that some companies with
exacting standards of quality would not want even traces of rancidity in
their products and would run their stores below -30ºC. I understand some
companies in Europe are already doing this, but you would be more familiar
with the cold storage situation than I am.
However, you are concerned with temperature of storage during shipping.
Distribution is certainly the weakest link in maintaining quality in the
frozen fish supply chain. At -18ºC frozen fish deteriorates about 4 times as
fast as at -30ºC. You refer to a standard of -29ºC; I don't think this is a
standards, more a recommendation. The EU Directives on frozen fish, and
frozen foods generally, require that they be held below -18ºC. I think the
US regulations also have this temperature, but perhaps someone closer to the
US situation could comment on this. The old ATP agreement on carriage of
frozen foods stipulated -18ºC, (is this agreement still in force, I could
not track it down on the Internet?). As you are well aware shipping
containers typically operate at -18ºC, though I believe some shipping lines
will offer a lower temperature at an increased charge. Reefers, again,
operate at -18ºC. The voyage time on a container ship might be about 2
weeks, but the container will be stuffed at the processing plant or store
before moving to the port, and delays due customs and other port formalities
at both the exporting and importing ends means that products might be 4
weeks or more in the container between cold stores. The quality loss in 4
weeks at -18ºC is equivalent to 16 weeks at -30ºC. Your containers, if they
do hold the product at -35ºC, will reduce this quality loss to the
equivalent of 2 weeks at -30ºC and would retain the quality of the product
during shipping.
Peter Howgate
----- Original Message -----
From: Steve Bryant <Steve_Bryant@thermoking.com>
To: <seafood@ucdavis.edu>
Sent: Tuesday, July 16, 2002 5:01 PM
Subject: Deep Frozen Seafood
> I am Steve Bryant, Global Director Product Marketing for the Thermo King
> Seagoing Container Refrigeration Division. We are a major supplier of
> refrigeration systems to the containerized shipping lines of the world.
We
> have recently developed a refrigeration system capable of maintaining
> transport temperatures for frozen products at -35C. The standard up to
now
> has been -29C, with transport actually taking place at -18C due to varying
> insulating capabilities of older containers. We are researching products
> that will benefit from transport and storage at these lower temperatures.
> We are aware that certain oily fish maintain higher quality for longer
> periods of time at lower temperatures. Our question is, are there frozen
> seafood products that will retain better quality at -35C than -29C? If so,
> what specific species/products are better off? Are there seafood products
> that should not be maintained at -35C?
>
> Your thoughts will be appreciated.
>
> Regards
> Steve Bryant
> Thermo King Corporation
> (952) 887 2203
>
>
>
This archive was generated by hypermail 2b29 : Tue Jul 16 2002 - 13:39:36 PDT