Natural food and beverage flavour enhancers - Natural Food Additives, Ingredients and Flavourings - page 83

author's laboratory have found no signifi cant differences in levels of glutamate
extracted after different soaking times (2, 6 or 12 hours), or from different water
types (soft versus hard). Extraction effi ciencies may be improved by pre-grinding
the seaweed before soaking.

Fermented soy products
Fermented soybeans are another traditional source of glutamic acid, in the form of
either miso (soybean paste) or soy sauce. Traditionally miso and soy sauces are
prepared from the fermentation of soy beans with no direct addition of fl avour
enhancers (such as MSG), fl avour or colour. In the Japanese soy sauce (shoyu),
traditionally the soy beans are fi rst mixed with wheat before undergoing a two-
stage fermentation process, the fi rst of which involves koji mould fermentation to
yield koji, followed by a brine fermentation to yield moromi (Lioe et al. 2007).
The koji fermentation utilises Aspergillus species that have high proteolytic
activity. The specifi c enzymes leading to the proteolysis are, to some extent,
species-specifi c. In the second stage of fermentation wild bacterial fermentation
also occurs, with Lactobacillus and Bacillus species.
There are three main types of shoyu, of which the umami taste intensities of
those of koikuchi and tamari shoyu were found to be twice as large as that of shiro
shoyu. Koikuchi is produced from equal amounts of soybeans and wheat, tamari
is produced using soybeans as the main ingredient, and shiro is made using
a relatively high ratio of wheat to soybeans. Shoyu fermentation takes at least
6-8 months, and during this fermentation it is likely that most of the proteins
(soybean and wheat) are hydrolysed into free amino acids and short peptides with
a molecular weight (MW) of less than 500 Da (Lioe et al. 2007). The Lioe study,
which compared the three types of shoyu, found no signifi cant contribution
of peptides to the umami taste and that the level of free glutamic acid, as well
as several sweet amino acids and sodium salt, were the key contributors to the
high intensity of umami taste (Lioe et al. 2007). Soy sauces will vary in levels
of glutamic acid, aspartic acid and other amino acids; this is largely dependent on
the species of Aspergillus mould and lactic acid bacteria favoured in the
fermentation.
Originally, miso and soy sauce would have been prepared from the same
soybean fermentation, the solid cake being pressed for the miso and the aqueous
solution pressed from the cake being the soy sauce. In this case, you would expect
the glutamate levels to be higher in soy sauce than the miso, as it is very water-
soluble. However, it should not be oversimplifi ed in this way as microbial strains
and fermentation conditions will now be specifi cally chosen to yield either miso
or soy sauce most effectively.
The level of glutamic acid in a range of soy sauces and fermented bean pastes
are given in Table 4.1. In the selection of soy sauces to utilise for fl avour
enhancement, or perhaps for salt reduction, as recommended by Kremer (2009),
the total sodium content of the sauce must be considered. In the experience of the
author, the sodium content of soy sauces sold in UK can vary from 3.6 to 7.2%
(w/w).

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