Dear Richard,
I do not have data for salting whole pilchards, however, you could
calculate salting times approximately from the following papers:
(1)Studies on anchovy salting. I Equilibrium considerations and
concentration profiles.
Zugarramurdi, A. and Lupin, H.M.
Lat. am. j. chem. eng. appl. chem. 6: 79-90 (1976) (paper in Spanish and
English)
(2)Studies on anchovy salting. II Dynamics of the process.
Zugarramurdi, A. and Lupin, H.M.
Lat. am. j. chem. eng. appl. chem. 7: 25-38 (1977) (paper in Spanish and
English)
(3) A model to explain observed behavior on fish salting
Zugarramurdi, A. and Lupin, H.M.
J. of Food Science 45(5): 1305-1311 (1980)
The second and third paper contain salting rate constants (1/sec), as it
could be expected it yields "effective" diffusion coefficients lower than
those of NaCl in pure water. Salting "rates" depend on a number of factors
(e.g. presence/ absence of scales and fat layers, fish salted gutted or
whole, dry or wet salting process and if fish is pressed or not during
salting). However, above all for a given situation, the salt content at a
given point (e.g. guts or center of the fish that is the most unfavorable
condition) depends on the thickness (or "diameter") of fish to salt.
There is an important difference between salting of gutted fish and
salting of whole fish. In the case of salting of gutted fish the equilibrium
achieved is an ordinary chemical equilibrium (inside and outside of the
fish), in the case of whole salted fish the equilibrium reached is an
osmotic equilibrium (produced by the fish skin). This has importance in two
main aspects.
The first one is that concentration in the muscle at equilibrium will
not be the same in both cases (even if the external control brine is
saturated). The concentration of NaCl at equilibrium in whole fish (Aw >
0.75) will be higher than in gutted fish (Aw = 0.75). The second aspect is
that the salting rate (due to the difference in overall mechanism) is
quicker in whole fish (equilibrium of charges at both sides of the membrane)
than in gutted fish (equilibrium of chemical species in a "mixture" not
separated by a membrane).
The difference is created by the soluble substances in fish that can not
migrate through the fish skin (we called them in general "proteinates" even
if there is a number of different substances). We found some correlation
between the influence (e.g. partition coefficient at equilibrium) and the
non-protein nitrogen (NNP). Since NNP differ between species the actual Aw
inside whole salted fish can not be predicted beforehand as it is the case
with gutted (or cut) salted fish where Aw= 0.75 at equilibrium (if a
saturated brine is outside the fish).
There is a number of practical implications for all that. The first one
is that whole salted small pelagic tend to spoil, this can be observed in
the surface of the salting bats, because of the development of xerophilic
(black) fungus, a similar problem that can appear in any case when salt is
not enough to assure saturation. Of the possible fungus that can grow in
such a conditions some of them have been proved to have histamine forming
capacity (even if at a reduced rate when compared with bacterial histamine
formation rates at the same temperatures).
An additional point is fish size. If the the whole fish to salt is a
large fish (e.g. hake or cod) then the main diameter is much larger, and
there may be possibility of toxin formation by C. botulinum. I have a seen
some epidemiology reports due to intoxication from toxin of C. botulinum due
to consumption of whole salted hake (this a sort of traditional ethnic fish
product that may be eating without cooking). Large fish, in general when
salted whole spoils before complete salting and you notice it (it is spoiled
fish salted), but hake has a sort of "limit" size and may not appear
spoiled.
An obvious additional factor is temperature. The higher the temperature
the higher the risk in this case.
Formation of toxin of C. botulinum particularly in demersal fish or in
aquaculture fish confined in ponds could happens as result of bad handling
and temperature abuse (lack of hygiene in ponds, etc), if there are not many
problems due to that (particularly in the pre-HACCP era) was (is) due to the
fact that most of this type of fish is cooked before consumption, therefore
the toxin, if there, is destroyed.
However, in the case of the "whole pilchard" you mention I assume that
you are referring to an anchovy "analog" that may be consumed raw (also
cooked if put in pizzas) and from here the hazard of toxin of the C.
botulinum.
I do not know what does it mean "dry" in this case (perhaps pressed?).
If you dry a salted anchovy or pilchard it will finish rancid very quickly.
During salting due to reduction in water, high salt content and change in
configuration properties of the proteins, fish oil tend to be released and
oxidize very easily (NaCl also catalyze the oxidation reaction). Drying,
will reduce the Aw.
Therefore salting time in the point you are asking for would depend on
the main "diameter" of the "pilchard" you mention, and also in the rest of
conditions discussed here. Size is very determinant in this case, and I do
not know the pilchard to which you refer to. I have seen fish called
"sardines" that are salmon size.
To salt whole fish (small or large) is a risky exercise anyway. In
tropical o semi-tropical conditions (above 21 C) it may be unlikely that 3 %
of salt in the water phase in the riskiest point could be reached in less
than 4 hours as suggested in the FDA Fish and Fisheries Products Hazards and
Controls Guide (2nd Edition) (Table#A2).
If you put all the things all together and you continue to have doubts
about your raw material, handling, etc. then the recommendation would be to
salt always gutted fish, in this case salt will be immediately in contact
with the riskiest point inside the fish.
Well, zero risk is a thing that does not exist, but I would not be too
much worried about the risk of toxin of C. botulinum in gutted salted small
pelagic with, say maximum "diameter" about 2.5 cm, or 1.25 cm of saturated
salt to the most unsafe point (e.g. traditional anchovies).
Of course this will be of not help if the toxin has been formed before.
However, this is more likely that happens (or be more riskier) either in
demersal fish (taking C. botulinum from the sea bottom) or in fish from
ponds. Pelagic fish that lives in the surface of the sea should be (in
principle) less prone to present C. botulinum of contamination.
Kind regards.
Hector M. Lupin
Senior Fishery Industry Officer (Quality Assurance)
Fish Utilization and Marketing Service
Fishery Industries Division / FAO of the UN
Viale delle Terme de Caracalla 00100 Rome Italy
Tel.: +39 06 570 56459 Fax: + 39 06 570 55188
E-mail: hector.lupin@fao.org
Please visit our website: http://www.fao.org <http://www.fao.org/>
-----Original Message-----
From: Richard Chivers [mailto:richard@fishonline.co.uk]
Sent: Thursday, May 24, 2001 11:07 AM
To: seafood
Subject: Salt penetration in pilchards
Does anyone have figures on the time taken for salt to penetrate to the gut
of dry salted whole pilchards. I am looking for control over C. botulinum,
so 3.5% in the water phase.
Richard Chivers
Fisheries Consultant
Seafood Audit International
44 (0) 1823 666666
www.fishonline.co.uk <http://www.fishonline.co.uk>
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