Natural food and beverage flavour enhancers - Natural Food Additives, Ingredients and Flavourings - page 77

genetic difference is unlikely to be the cause of discrepancies in umami-salt
enhancement. It is perhaps more likely that the tasters in the West, who are less
accustomed to the umami taste, may detect an overall increase in savoury taste of
a product that contains umami tastants but accredit this to salt taste rather than to
umami taste. Perhaps the basis of increasing umami taste to compensate for salt
reduction is founded more upon the reduction of 'blandness' through use of
umami rather than true enhancement of salt taste perception by umami stimulants.
In addition to the effect of umami taste as a fl avour enhancer, it can also
increase the liking of fl avour, by means other than increased perception. In a study
by Prescott (2004) using three separate consumer groups (total n = 69), liking for
a novel fl avour was signifi cantly increased when that fl avour was paired with
glutamate and the combination was ingested, in comparison to the groups which
tasted the fl avour alone, or with glutamate but expectorated. This study suggests
a reward mechanism for glutamate, perhaps as glutamate signals for essential
amino acids or for protein. However, from a food manufacturer's perspective this
can double the benefi t of using a savoury fl avour enhancer to boost the savoury
fl avour and to result in a 'moreish' product.

4.2.1 Umami amino acids
The two amino acids that impart umami taste are glutamic acid and aspartic acid.
However, aspartic acid has only 0.077 times the relative umami taste compared
with glutamic acid (Yamaguchi et al. 1971). They are both non-essential amino
acids that are present in abundance as free amino acids in many foods. Approximate
levels found in various food ingredients are given in Table 4.1.

Seaweed
As can be seen in Table 4.1, the levels of glutamate in seaweed vary substantially,
with levels being highest in Japanese kombu ( Laminaria japonica or Saccharina
japonica ). It is not clear why the levels vary between genus and species. Within
the kombu family, the glutamate level in Japanese kombu has been found to be
higher than in Irish kombu ( Laminaria digitata ); although this may be due to
species difference, it could also be due to environmental factors.
Other factors that may affect the glutamate levels in seaweed are the time at
which the kelp is harvested; it is likely that the free amino acids will be utilised or
accumulate during different stages of the seaweed lifecycle, from either the
reproductive or growth stages for example. In addition, post-harvest and drying
conditions of the seaweed vary, and anything which might cause proteolysis of the
seaweed, such as fermentation, might alter glutamate level. In Japan, kombu can
either be sun-or air-dried; is often left to mature for up to one year and can be
further matured in cellars for up to 10 years (Blumenthal et al. 2009).
The manner in which the seaweed is utilised within food preparations will also
affect the available glutamate. Traditionally, Japanese chefs soak kombu for
varying lengths of time (1-12 hours), at varying temperatures, and have a
preference for soft water (Blumenthal et al. 2009). However, experiments in the

￿ ￿ ￿ ￿ ￿