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

If mechanical heat drying is to be used, a moisture-tight
container through which dry air with less than 20% moisture
and approximately 40ºC is circulated until the moisture in the
natto reaches 8% or less. If the drying temperature exceeds
60ºC, fl avor and coloration are affected unfavorably.
(b) Natto hishio: Rice koji and table salt are added to
natto and weighted for 2-3 weeks until ripened. Kombu,
ginger, dried daikon, and salt-pickled vegetables are
sometimes also added. The usual ratio of natto to rice koji to
salt is about 5:4:1.
(c) UNICEF Powder: The Japanese Ministry of
Agriculture and Forestry’s Food Research Center under
request from UNICEF for 3 years starting from 1959 cooperated
in research to develop a dried powder form of natto.
It is a “predigested” high soy protein powder in which the
soybean structure has been softened by a short fermentation
by natto bacteria.
The product process is the same as for natto, except
that its fermentation is cut short at 6-8 hours, it is then
press-ground to noodle shape, the moisture level is reduced
to 4% or less at a reduced atmosphere of 30mmHg or less,
and fi nally ground fi nely in impact-type mills. The resultant
product is a powder of light yellow color and comparatively
low moisture sensitivity, it has no soybean smell but rather a
light fragrance and delicate fl avor, and has a relatively great
storability. Table 8.9 compares the composition of UNICEF
Powder and cooked soybeans. A biscuit containing UNICEF
Powder was production- and taste-tested, with the result
reportedly being that the failure rate was high for biscuits
containing 30% or more of the powder, and that the taste was
acceptable up to about 15%. A trial of these 15% UNICEF
Powder biscuits was then run on school children to ascertain
their taste acceptability over a 30 day period and it was
found to be liked by all, regardless of grade level or sex.
Moreover, Kosuge (?), et al. succeeded in isolating
a compound called tetramethylpyradine from natto, a
compound with a strong ability for sublimation and whose
smell at certain strengths greatly resembled that of natto;
it is supposed that it is one component of the natto’s
fragrance. An illustration shows the chemical structure of
tetramethylpyradine.
(b) Natto’s sticky fi laments: Natto’s sticky fi laments are
living compounds made by the action of natto bacteria on
the components of the soybean, mixtures of glutamic acid
polypeptides and furakuton (?) of layered furakutosu (?).
While the comparative amounts may fl uctuate, the former
is said to comprise 60-80% of the whole, strong fi lament
formation being accounted for by the polypeptides and
furakutau (?) contributing towards a normalized level of
stickiness. In investigating these glutamic acid polypeptides,
the surface of the natto was rinsed with approximately its
volume of water, the resulting dilute fl uid was then separated
in a centrifuge, the lighter upper liquid of which was further
passed into a cellophane membrane, and fi nally dropped into
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HISTORY OF NATTO AND ITS RELATIVES 201
methanol, forming sticky particles whose molecular weight
was approximately 15,000; Thus, it is estimated that these
are clusters of some 100 molecules of glutamic acid.
It has been shown experimentally that these sticky
fi laments are made by natto bacteria working on L-glutamic
acid. The glutamic acid that composes these sticky fi laments
includes D-shape glutamic acid, which comprises anywhere
from 20-80% of it. The sticky fi laments make up about
2% of the natto on a dry-weight basis, and at their most
stable level have a pH of 7.2 to 7.4, though the stickiness
becomes weaker at a greater alkalinity or acidity. For
example, on fl avoring natto for the eating, the addition of
table salt, rather than of shoyu, will produce more fi laments.
The greatest reason for natto whose fi lament formation is
weak is contamination by unwanted bacteria or by a natto
bacteriophage, etc.
(c) Natto enzymes: Within each 1 gm of natto there
are approximately 10 million natto bacteria which produce
large amounts of enzymes. Of each type of enzyme, the
strongest are those enzymes for breaking down proteins, and
in particular, alkaline proteinase as has been crystallized by
Mitake, et al. This crystalline proteinase shows the highest
level of activity at pH 8.2 and at 55ºC, and though it is
stable at pH 5-8, if the temperature rises to 55ºC and above
it becomes unstable, and it is destroyed when heated for 10
minutes at 65ºC and above. Its digestive strength on casein
is said to be stronger than that of commercial preparation
pankureachin (?). Also, the action of such enzymes such as
amylase, cellulase and lipase in natto are strong.
(d) Natto’s nutritional and medicinal values: Natto
enjoys the reputation of being high in nutritional value,
perhaps the greatest reason given is that in a rice-centered
diet like that of Japan, such soyfoods as natto are of great
importance as protein sources. Though the main nutritional
components are that of the soybean itself, as was previously
stated in natto, the breakdown of the soybean structure
and digestion of the protein are fairly accomplished, thus
the digestibility is increased. According to the research of
Hayashi et al., the digestion and absorption rate of white
mice fed a diet of 68 parts white rice and 28 parts natto and 4
parts inorganic salt was 93.2% broken down compositionally
to 86.8% protein, 89.8% fat, and 97.4% sugars, much higher
than for cooked soybeans. In vitamins, a notable increase of
vitamin B-2 to a level 5-10 times that before fermentation
or approximately 1 mg per 100 gm of natto is found. Also,
30% of the vitamin B-1 inactivated during pressure cooking
is reactivated during fermentation. Further, there is much
discussion about the effects of the digestive enzymes stored
in natto, however, we have not been able to locate any
research as to whether these enzymes produce benevolent
effects within the body. Although there is much tentative
evidence and basic research to the effect that natto is helpful
in the prevention and cure of such contagious diseases as
dysentery and intestinal typhus, at present it is still uncertain