Natural food and beverage flavour enhancers - Natural Food Additives, Ingredients and Flavourings - page 76

within two areas of the cortex (medial orbitofrontal and pregenual cingulated)
than could be achieved by the sum of the activations produced by the taste or
odour components when presented separately. Their paper also highlighted that
this enhancement only occurred with consonant odours, i.e. with fl avours
perceived as savoury not sweet. Although such a supralinear effect could also be
found with salt and savoury fl avours, the effects were substantially less than the
effect found with glutamate.
Whether the umami taste acts synergistically or not with other basic tastes is
still under debate. At threshold levels and in pure solutions, the presence of 5mM
monosodium glutamate (MSG) had no effect on taste thresholds for sweet
(sucrose), salt (NaCl) or bitter (quinine sulfate); however, a 5mM solution of the
umami 5′-nucleotide, IMP, slightly raised the bitter threshold (Yamaguchi and
Kimizuka 1979). Both MSG and IMP raised the sour threshold (tartaric acid),
though this would have been due to the subsequent rise in pH as the system was
unbuffered. At suprathreshold levels, the same authors found additional effects.
The umami intensity of MSG was substantially suppressed by sweetness (sucrose)
and bitterness (quinine sulphate), but less affected by salt (NaCl) and slightly
lowered by sourness (tartaric acid). Conversely, high levels of MSG slightly
suppressed the perception of sweetness, sourness, more substantially suppressed
bitterness and had a very slight effect on increasing salt perception at high MSG
levels.
Within real foods the situation becomes more complex, but there is gaining
acceptance that umami can increase salt perception (Kremer et al. 2009; Methven
et al. 2010), and utilisation of umami taste to combat salt reduction in foods is a
strategy that has been promoted to the food industry (CTAC 2009). The Kremer
study was based on using soy sauce as a salt replacer in three food types; salt was
reduced by 17-50% depending on the food, without any signifi cant loss in overall
taste intensity as perceived by over 50 consumers. The authors proposed two
potential mechanisms, either salt enhancement by the glutamate in the soy sauce
or by odour-induced saltiness enhancement (OISE) by a salty congruent odour.
The latter hypothesis had been previously explored in model water/salt/fl avour
systems by Djordjevi et al. (2004) and Lawrence et al. (2009). However, Mojet, a
co-author on the soy sauce paper, had previously found umami tastants to enhance
salt perception in chicken broth (Mojet et al. 2004).
The study by Methven (2010) found that increasing umami tastants, through
use of natural ingredients, within a minced beef formulation at maintained sodium
level, signifi cantly increased salt perception of the products by a trained sensory
panel. One reason for this apparent discrepancy between studies could be the
experience, ability and ethnicity of the tasters. Firstly, there are genetic differences
in the ability to taste glutamate. Lugaz et al. (2002) described three types of
people: glutamate tasters, non-tasters and hypotasters. Non-tasters can taste the
sodium in MSG but not the glutamate, and hypotasters have taste detection
thresholds for sodium chloride and MSG at the same molarity so it is not possible
to determine whether they are tasting the glutamate or the sodium. However, as
the sodium levels were kept constant in the Kremer and Methven studies, this

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