ARCHIVES,
FISHERIES AND MARINE SERVICE
Translation Series No. 3734
On the phenomenon of ropiness in marinated
fried herring
by K. Priebe
Original title:
From:
Uber die Erscheinung des Fadenziehens bei Bratherings
marinaden
Allg. Fischwirtschaftsztg. 22(1): 130-133, 1970
Translated by the Translation Bureau( UA )
Multilingual Services Division
Department of the Secretary of State of Canada
Department of the Environment
Fisheries and Marine Service
Biological Station
St. John's, Nfld.
ment 01 FUMert
00. e oeens.
Library
1976
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DEPARTMENT OF THE SECRETARY OF STATE
SECRÉTARIAT D'ÉTAT
TRANSLATION BUREAU
BUREAU DES TRADUCTIONS
MULTILINGUAL SERVICES
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r.
TRANSLATED FROM - TRADUCTION DE
))
re
:373y
INTO - EN
English
German
AUTHOR - AUTEUR
Priebe, K.
TITLE IN ENGLISH - TITRE ANGLAIS
On the Phenomenon of Ropiness in Marinated Fried
Herring
TITLE IN FOREIGN LANGUAGE (TRANSLITERATE FOREIGN CHARACTERS)
TITRE EN LANGUE ÉTRANGÈRE (TRANSCRIRE EN CARACTÉRES ROMAINS)
Uber die Erecheinung des Fadenziehens bel Bratheringsmarinaden
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Allgemeine Fischwirtschaftszeitung
REFERENCE IN ENGLISH - RÉFÉRENCE EN ANGLAIS
Journal of Fish industry
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1970
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130-133
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Allgemeine Fischwirtschaftszeitung (Journal of Fish Industries)
22 (1) : 130-133, 1970
From the State Veterinary Office Bremerhaven,
Director: Veterinary Director Dr. V. Kietzmann
On the Phenomenon of Ro mess in Marinated Fried Herring
by K. Priebe
The principal concern of producers of marinated fried
herring is the occurrence of ropiness in these products.
In 1942, Kachler reported the results of studies
on ropy marinated fried herring. From the ropy product,
various species of aerobic spore-formers were isolated
which were characterized by slimy-ropy growth when cultivated
on various media.
Since that time these microorganisms were
regarded as the cause of ropiness in marinated fried herring.
This assumption of à causal relationship between the aerobic
spore-formers and ropiness in marinated fried herring was
based on the knowledge of ropiness in bread, where it was
considered as proven that aerobic spore-formers are the
cause of ropy bread.
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Kachler determined that theae microolganisms
originated from the mixture used for coating the herrings
before frying.
In order to eliminate spoilage, it was
therefore required when commercially producing marinated
fried herring that the coating equipment be physically
separated from the facilities for frying and filling the
tins.
This served to protect the final product from sub-
sequent contact with flour dust and the bacteria contained
in the flour before the tins were sealed. However, it was
evddent already from Kachler's experiments that it was not
*
always possible to produce artificial ropiness in these
products when using a coating to which aerobic spore-formers,
isolated from ropy marinated fried herring, had been added
or when the contaminated coating mixture was added to the
marinated product after the frying process and before the
tins were sealed.
The increasing and continuing occurrence of this
phenomenon in one production enterprise prompted new studies
on this problem.
In microscopic studies of the ropy infusion liquid
in marinated fried herring, predominantly rod-shaped,
but
also coccal microorganisms are found. However, other
strongly stainable substances, which probably originate
from the coating, interfere to such an extent that accurate
morphological data on the microorganisms present can only
rarely be obtained.
The results of culture examinations on rooy
3
ed.
marinated fried herring regularly show 'the presence of a
large number of lactic acid bacteria and, In addition,
of coccus-shaped microorganisms. Aerobic spore-Corniers
are rar elY
found and then usually only in small numbers.
According to a roueh estimate, the proportion of nonlactobacteria to the total microorganisms contained in ropy
marinated fried herring usually is less than 10 %.
Based on these findings, Kachleris results, which
indicated that aerobic spore-formers cause ropiness of the
infusion liquid in marinated fried herring, seemed questionable, end renewed studies were therefore initiated.
In
these studies the criterion used to assess the ability
.
of microorganisms to produce ropiness in marinated fried
herring was the ropiness observed in fully sterilized
tins of fried herring,which had been inoculated with a
suspension of the species of organism in question and then
incubated. By contrast, Kachler regarded the aerobic
spore-formers, isolated from ropy marinated fried herring,
as the cause of ropiness if they showed slimy-ropy growth
in solid or liquid nutrient media. In our opinion, using
fully sterilized tinned fried herring •for testing a species
of microorganism for its ability to produce ropiness is
more adventageous than using marinated fried herring.
Because the tinned fried herring is sterile, no confounding
influences by other species of microorganisms, which normally occur in marinated fried herring and may affect the
result, would be expected when the tin is inoculated.
4
Fully sterilized tinned fried herring can essentially
be regarded as a product of the same composition as marinated
fried herring. Therefore, bacteria which cause ropiness
In the former product can also be considered as the cause
of ropiness in the latter.
In one experiment 15 strains of bacteria were isolated from various ropy marinated fried herring. Each strain
was increased on the respective medium suitable for its
growth, elutriated with a peptone sodium chloride solution
and inoculated into the tin of fried herring by puncturing
the tin with a hypodermic syringe.
with solder.
The puncture was sealed
The inoculated tins were incubated at 30°C
for 10 days. After inoculation and incubation the contents
of the tins were tested for ropy consistency.
Of the 15
bacterial strains tested, 5 belonged to the aerobic sporeformers, 5 to micrococci, and 5 to lactobacteria.
With all strains of the aerobic spore-formers
and micrococci tested for ropiness,the infusion liquid
of the inoculated tinned fried herring remained watery,
although especially two of the aerobic spore-formers tested
were characterized by viscous growth of the colony on simple
nutrient agar. The inoculum of four of the five strains
of lactobacteria produced a slimy-ropy consistency of the
infusion liquid or coated surface of the herrings. These h
strains of lactobacteria causing ropiness were found to be
homofermentative.
On Parnes agar and sorbic acid agar,
5
moreover, three strains were characterized by a viscous,
ropy consistency of the colonies that were glassy-colourless
or were the colour of the medium. However, one homofermentative lactobacterial strain that caused ropiness lacked
this characteristic consistency of the colonies. Another
lactobacterial strain which did not cause ropiness was found
to be heterofermentative and did not show a slimy consistency
of the bacterial colony which had a whitish-opaque appearance.
During further studios the slimy-ropy consistency of the
colony, which disappears after three days of incubation
on Barnes or sorbic acid agar, and the glassy appearance
of the young colony in most cases were found to be good
rough markers for tentatively distinguishing the ropinesscausing lactobacteria, isolated from marinated herring,
from other lactobacteria.
In further studies it has been demonstrated that
these ropiness-causing, homofermentative lactobacteria
are also present in normal, i.e. non-ropy,marinated fried
herring. This fact indicates that the presence of these
microorganisms alone does not necessarily . indicate ropiness
in the product. Special consideration must be given to
factors of the medium (vinegar, salt, protein content,
carbohydrate content, pH value, other buffer substances,
accompanying flora, temperature). Ropiness never occurs
in all tins of the same production batches and under the
same storage conditions.
.r •
6
Experiments using artificial nutrient media in the
test tube instead of fully sterilized tinned fried herring
or marinated fried herring for testing bacterial strains
for their ability to cause ropiness have not yielded satisfactory results. Therefore, studies on these ropinesscausing microorganisms, when considering the various factors
of the medium which play a role in marinated fried herring,
should best be conducted on the commercial product. The
medium factors can possibly be altered in order to avoid
the occurrence of this defect.
The majority of these hamefermentative lactobacteria,
which regularly produced ropiness in tinned fried herring
inoculated with these bacteria, were shown in the differen-
tiation
*
to be StrutobALtArimn ElmIarum. In one case it
was SIreplobacterium ease i var. alactosus.
It must be
noted that only the colony of Streptobacterium plIntarum
is characterized by a viscous growth on Barnes agar or
other special nutrient media for lactobacteria.
Furthermore it was found in the inoculation experiments with StrfpLobacterium casei var. alactosus that
the degree of ropiness regularly was less pronounced than
with Streptobacterium p1antarum.
Streptobacterium plantarum had been found earlier
in marinated green and fried herring (Lerche 1960, Meyer 1962),
where some of the tins exhibited bulging.
However, no
* The author wishes to thank Prof. Dr. G. Reuter, Berlin,
Institute of Food Hygiene, Proie Universitilt, for his support
in the differentiation of the strains of lactobacteria.
7
statements are found regarding the relationship to ropiness.
Based on yet incomplete studi o s, Meyer (1968) recently
reported that he also succeeded in isolating Streptobacterium
plantarum and other not yet identified homofermentative
lactic acid bacilli from ropy marinated fried herrings,
which he identified as slime-formers. It is not mentioned
by what criterion these microorganisms were recognized as
slime-formers in marinated fried herring.
As the name
Implies, Strlatolut.nim 0a_r_zm, which is widespread
In nature, is a plant microorganism and participates in
many spontaneous acidification processes. It has been found,
besides other species of lactobacteria, in green herrings
which were bought inland (Krause 1961).
Species of micro-
organisms that are closely related to SIrepIonlçterium
EllnlInn et casei are found in slimy ham curing brines
(Deibel and Niven 1957).
Recently the species Streptobac-
ter•um plantarum var. viscosum was described as the cause
of ropiness of the salt brine used in the production of
cottage cheese (Chomakov 1967).
The recognition of these species of microorganisms
as the cause of ropiness in marinated fried herring motivated
studies on the behaviour of these microorganisms in culture
toward the medium factors that are important to the keeping
quality (vinepar content, table salt content, pH value,
preservntives, temperature).
In tests with those medium
factors most easily altered in the production of marinated
8
fried herring in order to suppress growth of these microorganisms, a relatively wide tolerance to table salt was
found, with growth retardation occurring only at
salt.
8 %
table
Mn-Ac fluid medium (Coretti and Somogyi 1965)
was used as a growth substrate. By contrast, no growth
of microorganisms was observed when the acetic acid content
in the Mn-Ac medium
was increased to 1.2 % (corresponding to a pH-value of 3.9).
These two important values for the growth limit of ropinesscausing species of microorganisms must be regarded as reference points.
Different tolerance levels certainly may
occur in other growth substrates and in the marinated fried
Although a much higher vinegar
herring itself.
content than the determined threshold value of 1.2 % is
used in marinated fried herring, the ropiness-causing
microorganisms are certainly still active.
Based on this test, the preservatives permissible
by food law for marinated fried herring do not promise
success in the control of ropiness when used in the allowable
concentration.
Even
twice the allowable concentration of
potassium sorbate and sodium benzoate showed no inhibitory
effect on the growth of these species of microorganisms.
By contrast, twice the allowable concentration of the
sodium salt of the PHB-ethylester and the PHB-propylester
clearly reduced the growth of microorganisms. However,
only the growth of qtreplobleterium easel var. alactosus
was inhibited completely by twice the permitted concentration
9
of the Na-salt of the PHB-propylester.
When testing the
effect of temperature on growth of these microorganisms,
no growth occurred at +10 ° C in the medium used.
In order
to avoid ropiness in marinated fried herring, a storage
temperature of less than +10 ° C, which should be attained
rapidly after the production process, would probably be
adequate.
Extensive inoculation experiments with ropinesscausing species of microorganisms on marinated fried herring
showed that the occurrence of this phenomenon of spoilage
is closely correlated with the weight ratio of fried herrina
to infusion liquid when the tins are filled.
The decrease in vinegar content (or rising pH value)
in the remaining infusion liquid of the finished marinated
fried herring is critically dependent on the amount of fried
herring added, due to swelling of the fried herring and to
protein buffering. Therefore, the.quantity of fried herring
should not exceed a definite ratio to the quantity of fresh
infusion liquid.
The conclusion of these experiments for the production
of marinated fried herring is that the amount of fried
herring added to the tin should not exceed 40 % of the
total volume of the tin when the vinegar content of the
fresh infusion liquid is about 3 % (corresponding to a pH
a-)r)rox.
value of 2.5).
The remainder of he tin should be filled
with infusion liquid. After swelling of the fried herring
/132
.t.
10
in the tin, the weight of the herring would be about equal
to the remaining infusion liquid. Aside from technological
irregularities, the vinegar content of this infusion liquid
would rarely be less than 1.8 % and the pH value rarely
more than 4.2 - )1.3.
In a product of such a composition,
the occurrence of ropiness in the remaining infusion liquid
is extremely rare.
It was also recognized from the results
of the inoculation experiments on marinated fried herring
that the titratable vinegar content in the remaining infusion
liquid in the tin after diffusion and swelling cannot alone
determine the presence or absence of ropiness. When individual experimental tins were compared, it was evident that
the level of vinegar content in the remaining infusion
liquid does not consistently determine the presence or
absence of ropiness.
The absence of ropiness in tins with
a relatively large amount of infusion liquid does not seem
to be due to the lesser dilution of vinegar alone. It is
due,to at least the same degree, to a greater dilution
of the substances which are introduced with the fried
herring in the coating mixture, serving as the origin
for slime formation.
Based on the present state of knowledge, particularly
after identification of the causal bacteria, there are
initially two ways to prevent the occurrence of ropiness
in marinated fried herring.
11
1.
Elimination of the causative streptobacterial
infection in tins of marinated fried herring before the tins
are sealed. Studies on the origin of the microorganisms
are not yet completed. However, previous control checks
at various stages showed that there are no massive sources of inbion
fection during proda' .0f the raw materials for the production of marinated fried herring, only unfried herrings
were found in isolated cases to have a low degree of infestation with streptobacteria.
No microorganisms have
been found tddate
in the remaining raw materials (vinegar,
A
flour, oniOns). Apparently, the phenomenon of ropiness
in the sealed tin can be induced by a minimum 'dose of microorganisms which in this product attains an optimum concentration and thus produces slime. It is quite possible
that a low content of these microorganisms in the air
is sufficient to induce the infection, similar to the
spontaneous lactic fermentations in nature (milk, cucumbers,
sauerkraut). Although it will hardly be feasible to elimi nate these microorganisms completely, it should at least bè
attainable to keep the rate of infection as low as possible,
particularly in the herring, as well as in all other ingredients in the tin after the frying process, by employing
operational measures in the form of continual sterilization,
disinfection of the air etc.
12
2.
Choice of a composition of marinated fried
herring which inhibits the development of the causative
microorganisms or their activity of slime formation.
Based on the studies conducted, the occurrence of ropiness
in marinated fried herring is particularly favoured when
the weight ratio of the content of the tin, fried herring :
infusion liquid, favours the fried herring.
In the final
product, i.e. after swelling of the fried herring in the
tin is complete , the weight ratio of fried herring to infusion liquid should not exceed the factor 1 (fried herring :
infusion liquid = 1 : 1 = 1.0).
If an average weight
gain of 25 % is assumed in the herring due to swelling,
the portion of the fried herring should not exceed 40 %
of the total net weight when the containers are filled;
the remainder (60 %) consisting of infusion liquid.
Example for calculation:
net
The tin has a totaleweight of 200 g. The portion
of fried herring of 40 % is 80 g. The remainder (60 %) then
must consist of infusion liquid (120 g).
After swelling
the weight of the herring has increased by 25 % = 20 g,
by which amount the infusion liquid has decreased.
The
weight of the fried herring now is 80 + 20 = 100 g ' as
compared to the remaining infusion liquid of 120 -. 20 = 100 g
(100:100 = 1 : 1 = 1.0).
Of course, a similar effect
can be attained when sealing of the tins is delayed by a
13
hours after filling.
The level of infusion liquid which
has dropped due to absorption by the herring can then be
refilled to the rim of the tin before the tin is sealed.
In our opinion, this method seems to be the most promising.
To what degree this method is employed, depends on technological and economic viewpoints together with an estimate
of the risk in occurrence of ropiness.
In addition, the
infusion liquid should contain the maximum, organoleptically
acceptable vinegar content, because it was shown that the
causative microorganisms are relatively susceptible to
acetic acid.
Since the vinegar content in the remaining
infuslon liquid of the final product depends essentially
on the weight ratio of the content of the tin, the weight
ratio, primarily, must be regulated. Furthermore,
the
storage temperature for marinated fried herring definitely
must not exceed 1- 10 ° C; it should best be maintained near 0 ° C.
Other aspects which may aid in the prevention of
ropiness Of the infusion liquid in marinated fried herring
are purely speculative at this time.
Spoilage can be elimin-
ated by killing the causative microorganisms by sterilization of the product after the tins are sealed, a method
that is used very successfully in the production of fully
sterilized tinned fried herring.
The development of suitable
and effective preservatives, which are unobjectionable orr,antenticallv and healthwise,
would certainly be of Interest
in the production of marinated fried herrJng.
The development
••
114.
of a coating that is free of carbohydrates or a mixture
which is different from the one presently used should
also be considered, because the activity of the ropinesscausing bacteria identified can be traced with a high degree
of certainty to the polysaccharid-containing substances
which enter the product with the coating.
Literature.
1. Chomak- ov, C. (1967):
Isolation of lactic acid bacteria causing ropiness of white
cheese brine
Milchwissensdraft 22, 569-573
2. Coretti, K. u. A. Somogyi (1965):
Mangansulfat-Natriumacetat-Medium (Mn-Ac-Medium zur
Ziichtung und Differenzierung der in Lebensmitteln vorkco menden Laktobazillen).
Fleischwirtschaft 45, 1176-482
3. Deibel, R. H. u. C. F. Niven, jr. (1957):
Studies on the Microflora of Commercial Ham Curing Brin
and their Significance in Curing
Proceedings II. Intern. Symposium on Food .MicrobiologY
London, Her Majesty's Stationery Office 1958
4. Kraus, J. (1961):
Kurze Mittellung über des Vorkommen von Laktobazill e
au! frischen Heringen
Archiv Lebensmittelhygiene 12, 101-102
•
5 echler, W. (1942):
• Mikrobiologische Untersuchungen über das Fadenziehen bei
Bratmarinaden
z. Fischerei 40, 129-144
l\ l.u
5. Lueormdbrea,g e_
r(s1 ade
9601 ) in Fischprâserven
Berliner Münchener Tierarztliche Wodienschrift 73, 12-14
1, Mey er, V. (1962):
Tiber Milchsi-iurebakterien in Fischrnarinaclen
Zbl. Bakteriologie I. Orig. 184, 296-301
5. Meyer. V. ( 1968 ):
liandbuch der Lebensmitteldremie, III. Band, zweiter Tell,
herausgegeben J. Sdiormüller, Springer Verlag, Berlin, Hei-
delberg, New York
Literature
2. Sulphate of manganese-sodium acetate medium (Mn-Acmedium for cultivating and differentiating lactobacilli
occurring in food)
4. Brief report on the occurrence of lactobacilli in fresh
herrings
5. Microbiological studies on ropiness in marinated fried
herring
6. Cause of bulging in tins of fish
7. On lactic acid bacteria in marinated fish
8. Handbook of Food Chemistry, Vol III, part 2