Natural food and beverage flavour enhancers - Natural Food Additives, Ingredients and Flavourings - page 84

Tomato
Tomatoes are a rich natural source of glutamic and aspartic acids. In fact the
ripening of tomatoes is believed by some to be partly determined by achieving the
ideal ratio of glutamic acid to aspartic acid of 4:1 (Ajinomoto 2003). Fresh
tomatoes vary in their glutamate content and this is partly determined by variety
(Oruna-Concha et al. 2007) and by stage of ripening (Inaba et al. 1980). The part
of the tomato is also important, with the central pulp (locular) containing higher
levels than the outer fl esh (pericap) (Inaba et al. 1980; Oruna-Concha et al. 2007).
Inaba et al. (1980) found the glutamic acid level in the pulp to increase from
20 mg/100 g in a green tomato to 74 mg in a pink tomato and 175 mg/100 g in a
fully ripe tomato. Similarly in the outer pericarp, the levels increased from 18
mg/100 g to 30 and 110 mg/100 g over the same ripening stages. As the amino
acids are water-soluble they can easily be removed from the non-aqueous parts of
the tomato such as the skin and fi brous material. This was shown experimentally
in the Oruna-Concha paper, where the aqueous taste fraction of the tomatoes was
separated from the non-soluble fraction by centrifugation. A similar approach is
taken commercially in preparing concentrated tomato taste extracts, such as the
manufacture of the Santé™ product by Lycored Ltd (Lycored 2005).

Cheese
Glutamic acid has recently been shown to be one of the most important drivers of
umami taste in fractions extracted from mature cheddar cheese (Andersen et al.
2010). The maturation of cheese involves proteolysis, which leads to an increase
in free glutamic acid. The highest levels are usually found in the Italian Parmesan
(the regional Parmigiano-Reggiano or Grana Padano), where the cheeses are
matured for 24-30 months. Typical levels of glutamic acid in Parmigiano-
Reggiano are 1200-1600 mg/100 g (Ninomiya 1998); at such high levels it is no
wonder that parmesan is typically fi nely grated and added as a seasoning in its
own right. Within cheddar cheese the level of glutamic acid has been found to
increase from 10 to over 180 mg/100 g over eight months of ripening. A later
study by Drake et al. (2007) analysed glutamate, IMP, GMP, sodium chloride,
lactic acid, propionic acid and succinic acid in cheddar and Swiss cheeses. Sensory
evaluation of the cheeses found that glutamic acid played the largest role in umami
taste, whilst organic acids, particularly succinic and to a lesser extent propionic,
also contributed to the umami taste. At subthreshold concentrations the
5′-nucleotides lowered the threshold of succinic acid (Drake et al. 2007).

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Pure monosodium glutamate
In 1908 Dr Ikeda patented the manufacturing process for monosodium glutamate
and started production at the Ajinomoto factory. Today Ajinomoto produces
monosodium glutamate in many parts of the world, starting with local raw
materials ranging from sugar cane and beet, to cassava, wheat, rice and corn.
Sugar is pressed or, in the case of cereals, starch is extracted and saccharised.
Resulting sugars are then fermented with glutamic acid producing microorganisms
such as Corynebacterium glutamicum , Brevibacterium lactofermentum

or