The Behavior of Taste Ingredients during Desalination of ...
Transcript of The Behavior of Taste Ingredients during Desalination of ...
日本 調 理 科 学 会 誌Vo1.40,No.5,329~336(2007)〔Note〕
The Behavior of Taste Ingredients during Desalination
of Salted Pacific Herring Ovary (Kazunoko)
Atsuko Kasuga Eiko Ogiwara Yasuo Aoyagi
Desalination using salt water of a low concentration is called "Yobi-shio", and many cookbooks recommend the
use of salt to desalt. Analysis of sodium, potassium, magnesium, free amino acids and 5'-nucleotides was carried
out after the desalination using water and NaCl solution, to clarify whether the elution of taste ingredients caused
by diffusion was the only factor affecting the taste and what kinds of taste ingredients were affected during the
desalination of kazunoko. Sodium and magnesium eluted at lower contents in desalination using NaCl solution than
using water, but potassium was not affected. Free amino acids in the soaking solution increased with time and that
of desalted kazunoko decreased. The sum of the total free amino acids in desalted kazunoko and that of the soak-
ing solution with desalination using water after 15 hours was 1.8 times that of kazunoko, but that using 3% NaCl
was not increased at all. Moreover, the contents of total free amino acids in desalted kazunoko using water after
15 hours was twice that using 3% NaCl solution. Among these free amino acids, the hydrophobic amino acids
which are said to be bitter occupied 70%. These results indicate that free amino acids were produced by protease
during the desalination using water.
Key word: kazunoko, Pacific herring, desalination, yobi-shio, taste ingredient
Salted or dried roe of the Pacific herring (Clupea pal-
lasi) is called "kazunoko" in Japan. Salted kazunoko gen-
erally sells well in the market. Kazunoko with its distinc-
tive texture and taste is one of the foods considered to be
indispensable for the New Year holiday in Japan because
it is said to assure prosperity for a long time. The spawn
is generally full of protein and fat. Kazunko contains a
much higher content of Vitamin E, EPA and DHA than
the fish flesh from Pacific herring (Suzuki, 1994). Kazu-
noko, however, is rich in cholesterol. Furthermore, kazu-
noko is usually preserved in salt for storage, and exces-
sive intake of salt is also a concern.
When we make kazunoko with taste, we must first ex-
tract the salt. The desalination method for kazunoko var-
ies in each home. Some homes desalt it by draining the
water for several hours, and some homes desalt it by
changing the water several times overnight. According to
a Japanese cookbook dealing with kazunoko, many books
("Kihon no osechi to syougatsu no omotenashi", 2006 ; "O
syougatsuryouri to nabe", 2006 ; "Kazoku ga yorokobu
osechiryouri", 2006 ; Asada, 2006) recommend the use of
salt to desalt. However expression of the concentration of
salt as "a little" or "appropriate" is not clear. Thus, the to-
tal time of desalination varies from 6 to 48 hours, and the
times for exchanging the soaking solution vary from 0 to
several times. When kazunoko is sold in the market, a de-
salination method using salt water of seawater concentra-
tion is often displayed on the package. Moreover, Kawano
(2006) reported that soaking in salt water removes salt
quickly from the kazunoko. Kazunoko desalted using wa-
ter is sometimes said to taste bitter.
Regarding the salt, desalination using salt water of a
low concentration is called "yobi-shio" or "mukae-shio" in
Japan. "Yobi-shio" has been performed with salted fish
such as salted salmon and salted mackerel, and with ka-
zunoko (Kawano, 2006). However, considering the phe-
nomenon of diffusion, it is unnatural that the desalination
effect is higher in salt water than in water. Shimizu and
Satomi (1933) had already clarified that "Yobi-shio" was
ineffective. Sakai et al. (Sakai and Miki, 1982 ; Sakai and
Suzuki, 1985) also reported that the mechanism of desalt-
ing from fish flesh depends on diffusion. However, "yobi-
shio" generally seems to be a suitable means, as disclosed
in the following reports. Sugita (1977) mentioned that, in
the case of desalination of salted salmon and salted cod-
fish with water, elution of a taste ingredient in addition to
salt occurs earlier in comparison with salt and that only
the surface salt elutes early. Kazunoko desalted using wa-
ter is sometimes said to taste bitter. We wondered
whether, during desalination of kazunoko, the elution
caused by diffusion was the only factor affecting the taste
and what kinds of taste ingredients were affected. There
are few reports of taste ingredients during the desalina-
* Junior College of Kagawa Nutrition University
** Kagawa Vocational College of Nutrition
*** Kagawa Nutrition University
inquiry Junior College of Kagawa Nutrition University
3-24-3 Komagome, Toshima-ku, Tokyo, Japan, 170-8481
TEL 03 (3576) 2964 FAX 03 (3576) 2964
(329)33
J. Cookery Sci. Jpn. Vol. 40 No. 5 (2007)
tion of kazunoko.
In this background, we examined the effect of "yobi-
shio" of kazunoko not only from the viewpoint of desalina-
tion but also from that of taste ingredients such as bitter-
ness and umami ingredients. After the desalination of
kazunoko with water and NaC1 solution, analysis of the
contents of sodium, potassium, and magnesium, free ami-
no acids was carried out. Moreover, sensory evaluation
was carried out to determine whether the panelists could
distinguish the seasoned kazunoko which was immersed
in seasoning solution after desalination with water and
NaCl solution.
Materials and Methods
1. Materials
Kazunoko of about 3 kg was purchased in 2005 and
2006 in a fish shop in Tokyo. All of them were Alaska .
products. They were cut into pieces of about 5 g to re-
move individual differences in form, size and salt concen-
tration and were to be desalted uniformly. They were
put in a plastic bag and stored in a refrigerator before
the experiments and sensory evaluation.
2. Reagents
The hydrochloric acid for the mineral analysis was of
super special grade, and the lanthanum chloride solution
and other mineral standard solutions were used as re-
agents for the atomic absorption analysis. The lithium ci-
trate buffer solution (pH 2.2, lithium ion concentration =
0.25 mol//), the buffer solution for the amino acid analy-
sis and the amino acid standard solutions were the re-
agents for amino acid analysis. All other reagents were of
super grade. These reagents were purchased from Wako
Pure Chemical Industries, Ltd. The water used in this ex-
periment was purified using Milli-Q Lab equipment (Ni-
hon Millipore K. K). The seasonings used for sensory
evaluation were as follows : Seafood flavor of Bonito fillet
extract (Honkatsuodashi, RIKEN VITAMINE Co., Ltd.),
Light soy sauce (Usukuchi shoyu, HIGASHIMARU
SHOYU Co., Ltd.), Alcohol-based seasonings (Takara
Hon-Mirin, TAKARA SHUZO Co., Ltd.), Japanese liquor
(Cooking Sake Fukuizumi, FUKUIZUMI SANGYO Co.,
Ltd.). The composition of the seasoning solution by vol-
ume ratio was Japanese-style broth (10 g seafood flavor
of Bonito fillet extract dissolved in 1,200 ml water) : light
soy sauce : boiling-off of alcohol-based seasonings : boil-
ing-off of Japanese liquor = 6 1 1 1.
3. Desalination methods of kazunoko
1) Investigation to determine how long and how many
timesaresuitableforexchangingthesoakingsolu-
tion,
About20g(4pieces)ofkazunokowereselectedat
randomandputintoa250-mZvolumeplasticbottlewith
100m乙ofwater.Afterlhour,theywereremovedfroln
thewater,placedinastaidessbasketwithoutstacking ,
anddrainedofwaterfor5m.in.Theywerethenplacedin
anotherbottlewithafresh100mZofwater .Rehydration
wascontinued,andtherehydrationprocedurementioned
abovewasrepeatedhourlyafterlto10hours.Another
periodofdesalinationwastriedtofindthemostconve-
nientdesalinationmethod.Onemethodwastochangethe
waterafter3,5,7,andghours,andtheotherwasto
changethewaterafter5and9hoursincomparisonwith
themethodinwhichwaterwasnotchanged.Alldesali-
nationswerecarriedoutatroomtemperaturearound24
℃withoutmovingthebottle.
2)Desalinationmethodforanalysis.
Desalinationofkazun .okowascarriedoutusingO.5%,1
%and3%NaClsolutionsassoakirlgsolutionsforanaly-
sisofsodiurnarldpotassium.Theseconcentrationswere
selectedforthefollowingtworeasonsthatthedesalina-
tlonuslngsaltwaterofseawaterconcentrationisdis-
playedonthepackageofkazunokoandthatHashimoto
andMurakami(2003)mentionedtheuseof1~4%salt
concentrationinthecaseof"Yobi-shio".
Foranalysisofmagnesiumandfreeaminoacids ,water
and3%NaClsolutionwereused・assoakingsolutions .
Eachsolutionwaschangedtwiceafter5and10hours ,
andthetotaldesalinationtimewas15hours.Allother
conditionswerethesameasmentionedabovein1).
4.Mineralcontent$
Thesodium,potassiumandmagnesiumcontentsof
eachsoakingsolutionelutedfromkazunokowerefiltered
withpaper5A(AdvantecTOYO,ToyoRoshiKaisha,
Ltd。)andthesolutionsweredilutedatappropriatetimes
withwater.Theywereanalyzedbythemethodde-
scribedintheStandardTablesofFoodCompositionin .
Japan,fifthrevisionandenlargededition(2005).ASpec-
traA55B(Varian,Ltd.)wasusedfortheatomicabsorp-
tlonspectrophotometeranalysis.Allthemeasurements
werecarriedoutinduplicateorsometimesintriplicate 。
5.Freeaminoacidcontents
Forthefreeaminoacidanalysisofthesolutions ,whole
sOlutionswerepassedthroughacolumn(2φ ×15cm)of
cationexchangeresins(IR120,0reganoCo.).Afterrins-
ingwith100mZofwater,freeaminoacidswereeluted
with2mol/乙ammoniasolution.Lithiumcitratebufferso一
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The Behavior of Taste Ingredients during Desalination of Salted Pacific Herring Ovary (Kazunoko)
lution (pH 2.2) was added up to an appropriate volume,
subsequently evaporating the solution to dryness. For the
free amino acid analysis of the desalted kazunoko, the
sample was homogenized (Polytron PT 10-35, Kinemati-
ka, Inc.) with 70% EtOH and the container filled to
200 ml with 70% EtOH. After being filtered with filter
paper (No. 3, Advantec TOYO) , 20 ml of the filtrate was
evaporated to a few ml and then defatted with diethyl
ether. Lithium citrate buffer solution (pH 2.2) was added
to an appropriate volume. The free amino acids were an-
alyzed using an amino acid analyzer (Hitachi Model 835).
6. Sensory evaluation
Desalination was planned with water and 3% NaC1 so-
lution at room temperature of around 24°C. A 5-times
amount of the solution vs. kazunoko was added to 216 g
(54 pieces) of samples in vinyl bags (32 cm x 38 cm).
Four vinyl bags containing the kazunoko and solution
were prepared, two bags for water and two bags for 3%
NaCl. All other conditions were the same as in the desali-
nation method for analysis. Next, the desalted kazunoko
samples were immersed in seasoning solution for 24
hours. For a sensory evaluation, the kazunoko samples
were separated from the seasoning solutions and were
then served on a plate.
The panel consisted of 18 males and females (1 : 2)
whose ages ranged from 20 to 50. They were the staff of
the cooking laboratory of the Kagawa Vocational College
of Nutrition. Three pieces of the kazunoko were served
in three sets of 54 paper dishes labeled "R", "5", and "T".
The triangle test was used to observe whether the panel-
ist could distinguish the taste of kazunoko which was im-
mersed in seasoning solution after desalination with wa-
ter and 3% NaC1 solution. Booths were used for the
sensory evaluations at 26°C.
7. Statistical analysis
The statistical analysis was carried out with binomial
distribution (p - 3) for the triangle tests and with two-
way layout analysis of variance for mineral and free ami-
no acids.
Results and Discussion
1. Investigation to determine how long and how many
times are suitable for exchanging the soaking solu-
tion.
We first performed this experiment to find which
method should be as easy and efficient as possible for de-
salination of our samples. Fig. 1 shows the sodium con-
tents of the soaking solution eluted from the kazunoko.
Fig. 1 Sodium Contents of Soaking Solutions Eluted from the Kazunoko
Each value shows the sum of the sodium contents of soaking solution eluted from the kazunoko.
0 : water was not changed 0 : water was changed hourly
A : water was changed after 3, 5, 7, 9 hours
U : water was changed after 5, 9 hours
Each value showed the sum of the sodium contents elut-
ed. When the water was changed hourly, sodium was
eluted earliest from the kazunoko, and after 5 hours, the
sodium content reached equilibrium. When the water was
changed after 3, 5, 7 and 9 hours, equilibrium was
reached after 7 hours, and when the water was changed
after 5 and 9 hours, equilibrium was reached after 9
hours. When the water was not changed once, desalina-
tion was not performed sufficiently and equilibrium was
reached after 4 hours. Based on this experiment, a mini-
mum two changes of water and immersion for more than
7 hours is clearly desirable for desalination at 24t . Based
on this result, we decided that the desalination method.
for a later experiment was to change the water twice af-
ter 5 and 10 hours and the total desalination time was to
be 15 hours.
2. Mineral contents
The data showed the mineral contents of the soaking
solution eluted from the 100 g kazunoko, and each value
was the sum of the mineral contents eluted.
Fig. 2 shows the sodium contents eluted with different
NaC1 concentrations. When the desalination was carried
out with water, the highest amount of sodium content
was eluted. The second highest was with 0.5% NaC1 so-
lution and then with 1% and 3% NaC1 solution succes-
sively. From the variance of analysis, there was a signifi-
cant difference (p<0.01) between water and 3% NaC1,
and significant differences (p<0.05) between water and
0.5% NaCl, and between water and 1% NaCl. This result
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Cookery Sci. Jpn. Vol. 40 No. 5 (2007)
Fig. 2 Sodium Contents of Soaking Solutions Eluted by Different NaC1 Concentrations
Each value shows the sum of the sodium contents of soaking solu- tion eluted from the kazunoko.
Li- - - water 0 0.5% NaC1 : 1% NaCl A : 3% NaCI
There were significant differences at p<0.01 between A and L, rho.
There were significant differences at p<0.05 between GI and Gd, 0.
was expected based on the phenomenon of diffusion.
Many kinds of minerals taste bitter in addition to salty
(The Chemical Society of Japan, 1999). Bitter taste
seemed to be related to the sum of the diameter of the
anion and cation (Beets, M. G. J., 1978). Moreover, Ezaki
et al. (2004) reported that the components which affect
the taste of salt were MgC12 and KC1 and that the tastes
of MgC12 and KC1 were bitter. Therefore, we attempted
to measure the contents of potassium and magnesium.
Fig. 3 shows the potassium contents of the soaking solu-
tions eluted by different NaCl concentrations. The elution
curves for potassium were similar regardless of the con-
centration of NaCl. The potassium content of 100 g kazu-
noko was about 50 mg, and all potassium eluted into the
soaking solution after desalination using any solution.
Therefore, potassium did not seem to affect the taste of
desalted kazunoko.
Based on the results of Fig. 2, because there was a sig-
nificant difference (p<0.01) between water and 3%
NaCl, water and 3% NaCl solution were used as the soak-
ing solutions for a later experiment . Fig. 4 shows the
magnesium contents of the soaking solutions eluted with
different NaC1 concentrations. The magnesium content of
the soaking solution desalted using 3% NaC1 was lower
in quantity than that using water. There was a significant
difference (p<0.01) between water and 3% NaCl. This
result was caused by the phenomenon of diffusion, which
was also indicated in the case of sodium. The magnesium
content of kazunoko was about 19 mg. Though other fish-
Fig. 3 Potassium Contents of Soaking Solutions Eluted by Dif-
ferent NaCI Concentrations
Each value shows the sum of the potassium contents of soaking
solution eluted from the kazunoko.
Ll- - - : water • 0.5% NaCl
0- - : 1% NaCl A : 3% NaCl
Fig. 4 Magnesium Contents of Soaking Solutions Eluted by Dif- ferent NaC1 Concentration
Each value shows the sum of the magnesium contents of soak- ing solution eluted from the kazunoko.
111- - - : water A- : 3% NaCl There were significant differences at p<0.01 between 71 and A
ery products include much more magnesium than kazu-
noko, they do not seem bitter. Furthermore , the magne-sium content of desalted kazunoko became lower than
kazunoko. The threshold of bitterness for magnesium sul-
fate, was reported (The Chemical Society of Japan , 1976) to be 4.6 mM, and this corresponds to 55 mg / 100 ml . The form of magnesium of desalted kazunoko was not
clear, but judging from the quantity, it seemed that the
quantity of magnesium in desalted kazunoko was not re-
lated to bitterness.
3. Free amino acid contents
Fig. 5 shows the free amino acid contents of the soak-
ing solution and desalted kazunoko per 100 g of kazunoko
after 5-, 10- and 15-hour desalination with water and 3
36 (332)
The Behavior of Taste Ingredients during Desalination of Salted Pacific Herring Ovary (Kazunoko)
Fig. 5 Effect of Soaking Solution on the Free Amino Acid Contents
kazunoko : solution after 5 hours : solution after 10 hours ni : solution after 15 hours
control : salted kazunoko * : significant difference at p<0. 01
% NaCl. The content of the free amino acids in kazunoko
was 64.5 mg per 100 g, and this was selected as the con-
trol. When the desalination was carried out with water,
the total free amino acid contents of the rehydration wa-
ter increased with time, and that of the kazunoko de-
creased with time. After 15 hours, 50% of the total free
amino acids of the control remained in the desalted kazu-
noko. The sum of the total free amino acid contents of
the solutions and those of the desalted kazunoko after 15
hours was 1.8 times that of the control. This result sug-
gested that the production and elution of free amino acids
from the kazunoko occurred during the desalination.
There are some previous reports (Fujii, 1994 ; Makinod-
an, 1993 ; Kaneko, 1992) on enzyme reactions in food with
a high salt concentration. Fujii et al. (1994) reported that
a self-digestion enzyme produced free amino acids in
squid Shiokara during ripening. Makinodan (1993) re-
ported that the effect of bacteria on the ripening of "shio-kara" seemed to be negligible. Kaneko et al. (1992) also
reported that not only free amino acids but also oligopep-
tides were increased in the ripening of salted preserves
by a self-digestion enzyme. In desalted kazunoko, oligo-
peptides might increase and contribute to its taste in some part.
To prove that the increase in free amino acids was
never caused by microorganisms, we measured the pH
and microbial flora of the soaking solution after 0, 3, 5
hours desalination of kazunoko using water at 24°C. Oth-
er conditions were the same as in the analysis of free
amino acid. As a result, the pH was constant (pH 6.0),
and the viable cell counts were under 30 c. f. u./ m/ of
soaking solution (n = 3). Our experimentation showed
that microorganisms had almost no effect on the desalina-
tion of kazunoko using water at 24°C.
When the desalination using the 3% NaC1 solution was
carried out, the total free amino acid contents of the re-
hydration water decreased with time. The sum of the to-
tal free amino acid contents of the solution and that of
desalted kazunoko was not increased at all. After a 15-
hour desalination with 3% NaCl solution, about 70% of
the total free amino acid contents eluted into the solution,
and only 30% of the total free amino acids remained in
the desalted kazunoko. Comparing the desalination using
water with desalination using 3% NaC1 solution, the con-
tents of total free amino acids remaining in kazunoko de-
salted with water was twice that with 3% NaCl solution.
There was a significant difference (p<0.01) between de-
salted kazunoko using water and 3% NaCl. These results
suggested the effect of a protease during the desalination
with water. The fact that free amino acids were not in.-
creased between desalination with 3% NaC1 solution illus-
trates that the protease could not function in this solution.
Though desalination with 1% NaC1 solution was not tried,
NaC1 might interfere with the reaction of the protease.
Based on the contents of free amino acids, it was clear
that the desalination with water produced a much higher
content of free amino acids. Moreover, too long a desali-
nation time was unfavorable because free amino acids
eluted out of the kazunoko. However, depending on the
taste of the amino acids left in the desalted kazunoko, one
cannot determine how much amino acid is desirable.
Concerning the compositions of free amino acids, Table
1 shows the free amino acid composition of the soaking
solution and desalted kazunoko using water and 3% NaC1
per 100 g of kazunoko. In kazunoko = control) , the total
free amino acid content was 64.5 mg, and the largest con-
tent of amino acid was leucine (13.2 mg) and then valine,
alanine and isoleucine (6.5 mg, 6.3 mg, 6.2 mg). These
hydrophobic amino acids occupied 60% of the total free
amino acids. After 15-hour desalination, the ratio of the
free amino acids in desalted kazunoko using water re-
sembled that using 3% NaCl solution, and leucine, phenyl-
alanine and isoleucine were the main amino acids. The
contents of hydrophobic acids in kazunoko desalted with
water and with 3% NaC1 solution were 22.6 mg and
11.9 mg respectively, and they occupied about 70% of
each of the total free amino acids. When the desalination
was carried out using water, the production and elution
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I Cookery Sci. Jpn. Vol. 40 No. 5 (2007)
Table 1. Free Amino Acid Composition of Soaking Solution and Desalted Kazunoko
mg/100 g of salted kazunoko
Control : salted kazunoko before desalination
of free amino acids from the kazunoko occurred. Espe-
cially, the leucine, phenylalanine, lysine and arginine con-
tents of the sum of the solutions and desalted kazunoko
were 2.3-2.8 times that of the control. Suzuki and
Suyama (1983) reported that taurine and glutamic acid
were major constituents of the free amino acids in fish
eggs, and taurine contents were 27.6-341 mg and glu-
tamic acid contents were 12.2-52.0 mg/100 g eggs.
They also reported that the total amino acids in the eggs
spawned in seawater were two to six times those of oth-
ers. In our examination, we did not show the taurine con-
tents because its retention time was very short. Howev-
er, if any, its content seemed to be only a few mg/ 100 g
in kazunoko. Our results were not consistent with theirs.
The reason seemed to be that kazunoko was, strictly
speaking, not fish eggs but ovaries and that various pro-
cessing methods such as removing blood and preserva-
tion with salt were performed.
As for the taste, especially a bitter taste, the "Amino
Acid Handbook" (2003) reported that the absolute
threshold and the differential threshold for leucine, phe-
nylalanine and isoleucine was 380 mg/100 ml 10%, 150
mg/100 ml 20% and 90 mg/100 ml 15%, respectively.
All analyzed data for kazunoko and desalted kazunoko
were lower than these thresholds. However, kazunoko
desalted with water is sometimes said to taste bitter.
Kawai (2003) reported that bitterness is reduced by so-
dium and is difficult to detect. Because there is scarcely a
salt taste in kazunoko desalted with water, bitterness
may be noticed. Moreover, a mixture of hydrophobic ami-
no acids and minerals such as potassium and magnesium
is expected to have some influence on the bitter taste . As for the Umami taste, the content of glutamic acid in
kazunoko was 2.7 mg, and after 15 hours, that of desalted
kazunoko decreased to 1.1 mg with water desalination
and to 0.3 mg with 3% NaC1 desalination. These contents
were very low compared with the data that the glutamic
acid of "Ikura" (salted roe of salmon or trout) was
18.6 mg/100 g (Fushiki, 2003). As the absolute threshold
of monosodium-glutamate is 30 mg/ d/ ("Amino Acid
Handbook", 2003), desalted kazunoko never has the
Umami taste. Besides, we also analyzed 5'-nucleotides
such as 5'-GMP, 5'-IMP (data are not shown) , but they
could scarcely be found. Fushiki (2003) mentioned the 5'-
IMP contents of various marine products. The 5'-IMP
content of "ikura" was 2.7 mg/100 g, that of sea urchin
was 2 mg and that of shellfish such as scallops and short-
neck clams was scarcely detected. If 5'-IMP might exist
in desalted kazunoko, a synergism with glutamic acid
would be expected. The data for Umami components in
kazunoko and desalted kazunoko have never been report-
ed until now.
4. Sensory evaluation
The triangle test was used to prove whether the panel-
38 (334)
The Behavior of Taste Ingredients during Desalination of Salted Pacific Herring Ovary (Kazunoko)
ists could distinguish the taste of kazunoko which was
desalted with water from that with 3% NaC1 solution.
The panelists who gave the correct answer in the trian-
gle test were only 4 of the 18 people. Most of them could not distinguish the taste of desalted kazunoko by the two
desalination methods. If a significant difference was rec-
ognized, we intended to ask for further discussion regard-
ing which method of desalination was preferable.
To clarify the reason why the panelists could not dis-
tinguish between the two desalination methods, the free
amino acids compositions were analyzed (data are not
shown) . The contents of free amino acids in the season-
ing solution were extremely high, and so, those of the
seasoned kazunoko immersed in that solution increased
more than 10 times after desalination. As a result, it be-
came clear that desalination with or without NaCl did not
have any relation to the taste of the kazunoko samples
which were immersed in seasoning solution.
Conclusions
When the percentage of NaC1 solution was increased in
desalination, less sodium and magnesium were eluted.
This allowed us to reconfirm that "yobi-shio" was ineffec-
tive for quick desalting. However, "yobi-shio" consider-
ably influenced the behavior of free amino acids during
the desalination. The sum of the total free amino acids of
desalted kazunoko and that of the soaking solution with
water after 15 hours was 1 .8 times that of kazunoko be-
fore desalination. However, when using the 3% NaC1, free
amino acids were not increased at all. Moreover, the con-
tent of total free amino acids in kazunoko dessalted with
water after 15 hours was twice that desalted with 3%
NaCl solution. Free amino acids seemed to be produced
during the desalination by protease. Among these free
amino acids, the hydrophobic amino acids which are said
to be bitter occupied 70%. The content of glutamic acid
which is said to have a Umami taste was very low, al-
though the content of glutamic acid during desalination
using water was slightly higher than that with 3% NaCl.
Therefore, the content of glutamic acid of desalted kazu-
noko did not affect the Umami taste without 5'-nucleo-
tides. Other Umami contents, namely 5'-nucleotides, were
scarcely found before and after desalination with any so-
lutions ; in other words, 5'-IMP was not produced during
the desalination.
In conclusion, we could clarify that "yobi-shio" of kazu-
noko did not increase the speed of desalination and that it
not only decreased the amount of elution of taste ingredi-
ents by diffusion but also controlled the action of prote-
ase.
Acknowledgments
We thank Keiko Ryuushi for her skilful assistance.
References
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(Received Nov, 1, 2006 Accepted Jul, 18, 2007)
数 の子の塩抜 き過程 における味成分 の挙動
春 日 敦 子 荻 原 英 子 青 柳 康 夫
和文抄録
低濃度の食塩水を用いた脱塩は"呼 び塩'と 言われ,多 くの料理本では数の子の塩抜 きに塩を用いることを薦めている。
塩漬け数の子の脱塩中に,拡散による味成分の溶出のみが数の子の味に影響する要因であるのか,またどのような味成分
が影響を及ぼされるかを明らかにするために,数の子を水と食塩水を用いて脱塩し,ナトリウム,カリウム,マグネシウ
ム,遊離アミノ酸,5'-ヌクレオチドの分析を行った。ナトリウム,マグネシウムは,水よりも食塩水を用いた脱塩の方
が溶出量は少 なかったが,カ リウムは食塩濃度とは関係がなかった。脱塩中に浸漬液中の遊離アミノ酸は時間と共に増加
し,数の子中の遊離アミノ酸は減少した。水で15時間脱塩した時の,数の子と浸漬液中の総遊離アミノ酸含量の合計は,
脱塩前の塩漬け数の子の総遊離アミノ酸含量より 1 . 8 倍多かったが , 3 % 食塩水を用いて脱塩した時は全く増加していな
かった。さらに ,水で 1 5 時間脱塩した時の数の子中の総遊離アミノ酸含量は , 3 % 食塩水を用いて脱塩したときより 2
倍多かった。これらの遊離アミノ酸の中では ,味が苦いと言われる疎水性アミノ酸が 7 0 % 占めていた。これらの結果は ,,
遊離アミノ酸が水を用いた脱塩中にプロテアーゼによって生成されたことを示唆 している。
キーワード:数の子,ニシン,脱塩,呼び塩,味成分
*女 子栄養大学短期大学 部
亭毒 香川栄養専 門学校
榊 香川栄養専 門学校
§連絡先 女子栄養大学短期大学 部 〒170 -8481東 京都豊島 区駒込3-24-3
TELO3(3576)2964FAXO3(3576)2964
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