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

acteria fermentation progresses the components of the
soybean break down and its structure softens, thus making
it easier to digest and absorb. Concerning the changes
occurring throughout this period (as shown in Table 8.5),
we fi nd that among the carbohydrates, the complete sugars
those reduced sugars released by 205% hydrochloric acid
hydrolysis, decrease from the beginning to the middle of
fermentation. From the start of heat production during the
fourth hour of natto’s fermentation when protein reduction
begins to the completion of ripening at 16-18 hours, we fi nd
that nearly 60% of the protein has been changed into water
soluble nitrogenous compounds, though only a relatively
minor approximate 10% have been reduced to amino acids.
The progressive stages of protein reduction are shown in
Table 8.6. After the sixteenth hour at which natto’s ripening
is generally thought to be complete, there is an increase
in ammonia production, bringing an increase in a distinct
ammonia smell.
(b) Changes in soybean structure caused fermentation:
Although the main changes in protein are as described above,
the changes in soybean structures brought about by the action
of natto bacteria are as in the summarized observations
reported by Iguchi, et al. While both uncooked and cooked
soybeans stained to a uniform brick color throughout by
Millon’s reagent (miron shikiyaku), it was clearly found that
natto is broken down progressively from the outer surface,
and on staining fat with Sudan III, both uncooked and
cooked soybeans showed a distribution of fat globules of
uniform size throughout the cell, but in natto’s outer cells,
the breakdown of the protein causes these fat globules to
fuse together into large clusters. Further, in the outer surface
of the soybean, it was shown that when the intercellular
material breaks down the state of decomposition has begun.
Note: Sudan III is a lysochrome (fat-soluble dye) diazo
dye used for staining of triglycerides in frozen sections,
and some protein bound lipids and lipoproteins on paraffi n
sections.
Saio et al. have observed under the electron microscope
the structural changes undergone by the embryonic leaf
of the soybean during the natto production process, and
according to their fi ndings, the components of the soybean
do not exist uniformly throughout the soybean; for example,
the bean becomes natto the protein bodies themselves are
broken up and fat droplets spill out into the intercellular
areas, though upon staining with osmium tetroxide (shisanka
osumiumu) stain it was found that the fat had already lost
the ability to maintain a droplet state and had permeated the
cellular structure itself.
8.1.7 Special components of natto: (a) Natto fl avor: The
fl avor of natto being produced by natto bacteria fermentation,
it is said that the main fl avor comes from substances broken
down from soybean proteins. As stated under the heading
of Compositional Changes During Fermentation, the
breaking down of soybean proteins under the action of natto
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HISTORY OF NATTO AND ITS RELATIVES 200
bacteria turns 50-60% of those proteins into water soluble
nitrogenous compounds, of which 10% are amino acids.
Table 8.7 on the distribution and isolability (ability to be
isolated) of the amino acids in natto shows that each amino
acid is different and that glutamic acid, said to be directly
related to fl avor, has a isolability of 11%, with a rather strong
0.36 gm per 100 gm of natto. In addition, such other amino
acids as threonine, tryptophan, leucine, valine, etc. have high
isolability.
Organic acids are also related to fl avor. As shown in
Table 8.8, acetic and lactic acids are in abundance, although
the same amounts are present in cooked beans. Those organic
acids that increase in fermentation are butyric, propionic,
and succinic (kohaku-san) acids, the production of butyric
acid being greatest in rice straw-wrapped natto. Occasionally
there will be a bitter taste or strong smell to natto, or a
mold-like spotting on its surface, the bitter taste coming
from a peptide having isoleucine at its nitrogen extremity,
and the mold-like spotting often being a crystallization
of tyrosine. Further, the main causal component of the
unpleasant smell, commonly referred to as “lazy fragrance”
(fushoko), is said to be isovaleric acid. That which known
as the smell of natto is related to the presence of the abovementioned
ammonia, organic acids, fatty acids, etc., as
well as to diacetyl (jiasechiru; IUPAC systematic name:
butanedione or 2,3-butanedione). Diacetyl increases along
with natto ripening, though it decreases with the storage of
the fi nal product. Note: Diacetyl is a natural by-product of
fermentation.
Tables show: 8.5 Compositional changes in natto during
fermentation (after 0, 4, 8, 12, 16, and 18 hours).
8.6 Morphological changes in nitrogenous compounds
(percentage of dry material, percentage of total nitrogen)
after 0, 4, 8, 12, 16, and 18 hours.
8.7 Amino acids in natto (per 100 gm) (total amino acid,
gm), isolable amino acid (gm, isolability %).
8.8 Organic acids in natto (Kibara et al.) (After 0, 3, 6,
9, 12, 15, 16 hours of fermentation, and after 1 or 2 days of
storage). For each time is given: Moisture (%), valeric acid
(or pentanoic acid), butyric acid, propionic acid, acetic acid,
levulinic acid (reburin-san), succinic acid (kohaku-san),
lactic acid. Note: Formation of sticky fi laments begins after
3-6 hours of natto fermentation. A strong smell is emitted
after 2 days of storage. Address: National Food Research
Inst., Tokyo.
582. Watanabe, Tokuji; Ebine, Hideo; Ohta, Teruo. eds.
1971. Nattô [Natto]. In: Tokuji Watanabe, H. Ebine and T.
Ohta, eds. 1971. Daizu Shokuhin [Soyfoods]. Tokyo: Korin
Shoin. 271 p. See p. 123-38. [Jap; eng+]
• Summary: Continued. 8.1.8 Natto-related products: (a)
Dried natto: Natto is either soaked in strong saltwater, or
sprinkled with table salt and left for 15-20 hours, at which
time it is spread out thinly in a container and sun-dried.