History of Natto and Its Relatives (1405-2012 - SoyInfo Center

y prefecture in the Tables of National Consumption, we fi nd
that in 1968 the average amount per capita spent that year on
natto was highest in Sendai at 967 yen, followed by others
such as Sapporo 719 yen, Fukushima 915 yen, Mito 871 yen,
Tokyo 489 yen, Nagoya 177 yen, Kyoto 183 yen, Osaka 98
yen, Hiroshima 139 yen, Matsue 144 yen, Matsuyama 78
yen, and Fukuoka [the furthest south, in northern Kyushu]
217 yen, the national average being 343 yen. While there
exist many large differences between the various in money
spent, we can see clearly that the consumption of natto has
spread nationwide.
8.1.2 Natto bacteria and their characteristics: Although
natto has a history of some 1,000 years, the history of
bacteriological research on the bacteria that produce natto
amounts to less than 100 years. The oldest bacteriological
study on natto-producing bacteria in Japan is thought to be
Yabe’s report in the 15th issue of the Journal of the Japanese
Chemists’ Society (1895) that he had succeeded in isolating
several strains of bacteria from natto.
From that time on, much research was carried out on
natto bacteria, but it was not until 1906 that Sawamura
successfully isolated from those natto bacteria a bacterium
which, when recultured on cooked soybeans, would
consistently produce the characteristic sticky fi laments and
fl avor of natto. Upon researching the morphological and
propagative characteristics as well as the physiological
makeup of this bacterium, he found it to be very similar to
Bacillus mesentericus and named the new strain Bacillus
natto Sawamura. This research ascertained that natto is
produced solely by the fermenting action of the natto
bacteria. The bacteriological characteristics of this strain are
shown in Table 8.1.
However in the 6th edition (1948) of Bergey’s Manual of
Determinative Bacteriology recognized the world over as the
authoritative classifi cation of bacteria, B. natto Sawamura is
listed under B. sublitis, whereas the 7th edition fails to list
it at all. In other words, as far as Bergey’s classifi cation is
concerned a sub-strain of B. subtilis is responsible for natto
fermentation. Be that as it may, culturing any of the bacteria
which closely resemble B. natto, such as B. subtilis, B.
cereus, B. megaterium, or B. mycoides, on cooked beans fails
to produce a product of natto’s sticky fi laments and fl avor.
The choice of strains to be actually used in producing
natto is carried out by testing which successfully produce a
natto with characteristic fi laments and fragrance. Moreover,
common to all natto bacteria chosen in this way are found to
be certain marked differences from other B. subtilis strains.
For example, while natto bacteria can neither germinate nor
grow without biotin, other strains of B. subtilis can. Further,
while a bacteriophage that dissolves natto bacteria has been
discovered, this bacteriophage has no effect on other strains.
Judging from evidence such as this even if natto bacteria
were to be classifi ed under B. subtilis, for all practical
purposes they are clearly a bacterial group having special
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HISTORY OF NATTO AND ITS RELATIVES 196
characteristics distinct from other B. subtilis strains.
8.1.3 Natto bacteria growth and soybean composition:
Natto bacteria grow well on cooked soybeans of course, but
they also grow well on other beans, and other foodstuffs of
plant origin such as grains. They can even grow on animal
foodstuffs such as meat, fi sh, and dairy products. However,
growth on plant protein is greater, as is the production of
sticky fi laments. As exhaustive research has been carried out
on the composition of nutrients needed for the germination
and growth of natto bacteria, and those nutritional
requirements are now clear. The result was that natto bacteria
use sugars, particularly dextrose, sucrose, glucose, etc. as
sources of carbon, and that sucrose was necessary not only
for bacterial growth, but also for the production of the sticky
fi laments. Soybeans are approximately 20% of carbohydrate
in composition, some 30% of that being sucrose, enough for
the growth of natto bacteria.
Protein, that is to say amino acids, are used as nitrogen
sources. Of these amino acids, natto bacteria fi nd glutamic
acid, arginine, aspartic acid, proline, etc. easy to utilize
whereas threonine, tryptophane, phenylalanine, methionine,
etc. are comparatively diffi cult. However of the amino acids
composing the soybean’s protein work better as a nitrogen
source does a culture medium of milk casein.
In regard to vitamins, natto bacteria require biotin, any
culture media lacking in biotin being incapable of causing
spore germination or growth of the nutrient cell (eiyo saibo).
Though certain bacteria classifi ed as belonging to the same
genus, such as B. subtilis, B. megaterium, and B. cereus, do
not require biotin, besides B. natto such other members of
the Bacillus family such as B. mycoides, B. pumilus, and B.
coagulans do not require biotin, while the absolute minimum
density of biotin necessary for natto bacteria growth is
0.18%, complete growth requires at least 18%. Other
vitamins particularly the B group, are useful in creating a
suitable growing medium for natto bacteria, and as shown
in Table 8.2, soybeans contain biotin suffi cient not only for
the germination of natto bacteria spores, but also for the
propagation of the nutrient cell, thus eliminating any need for
adding biotin in the production of natto.
8.1.4 Natto bacteria growth and environment: Beyond
a doubt the single most important thing in the production
of natto is to allow the natto bacteria to grow fully on the
cooked soybeans, however in order to achieve this, it is
also important to know what environmental conditions are
most conductive to the germination and propagation of natto
bacteria. In the production of natto, the natto bacteria used
are in the forms of spores, either in a liquid cells (eiyo saibo)
and fi nally proceed into cell division.
The optimum temperature for natto bacteria spore
germination is approximately 40ºC, most spores having
germinated and begun propagation within 2 hours on
a peptone-glucose culture medium, though at 50ºC the
germination is rather slow, and at 55ºC and above no