food chemistry / Kimia Pangan - Umami

FOOD CHEMISTRY
KIMIA PANGAN

Flavor Enhancement—Umami
Perasa Makanan - Umami 

A number of of compounds have the ability to enhance or improve the flavor of foods. It has often been suggested that these compounds do not have a particular taste of their own. Evidence now suggests that there is a basic taste response to amino acids, especially glutamic acid. This taste is sometimes described by the word umami, derived from the Japanese for deliciousness (Kawamura and Kare 1987). It is suggested that a primary taste has the following characteristics:

• The receptor site for a primary taste chemical is different from those of other primary tastes.

• The taste quality is different from others.

• The taste cannot be reproduced by a mixture of chemicals of different primary tastes.

From these criteria, we can deduce that the glutamic acid taste is a primary taste for the

following reasons:

• The receptor for glutamic acid is different from the receptors for sweet, sour, salty, and bitter.

• Glutamic acid does not affect the taste of the four primary tastes.

• The taste quality of glutamic acid is different from that of the four primary tastes.

·                     Umami cannot be reproduced by mixing any of the four primary tastes.

Monosodium glutamate has long been recognized as a flavor enhancer and is now being considered a primary taste, umami. The flavor potentiation capacity of monosodium

glutamate in foods is not the result of an intensifying effect of the four primary tastes. Glutamate may exist in the L and D forms and as a racemic mixture. The L form is the naturally occurring isomer that has a flavor-enhancing property. The D form is inert. Although glutamic acid was first isolated in 1866, the flavor-enhancing properties of the sodium salt were not discovered

until 1909 by the Japanese chemist Ikeda. Almost immediately,' commercial production of the compound started and total production for the year 1954 was estimated at 13,000,000 pounds. The product as first described by Ikeda was made by neutralizing a hydrolysate of the seaweed Laminaria japonica with soda. Monosodium glutamate is now produced from wheat gluten, beet

sugar waste, and soy protein and is used in the form of the pure crystallized compound.

It can also be used in the form of protein hydrolysates derived from proteins that contain

16 percent or more of glutamic acid. Wheat gluten, casein, and soy flour are good sources of glutamic acid and are used to produce protein hydrolysates. The glutamic acid content of some proteins is listed in Table 7-8 (Hall 1948). The protein is hydrolyzed with hydrochloric acid, and the neutralized hydrolysate is used in liquid form or as a dry powder. Soy sauce, which is similar to these hydrolysates, is produced wholly or partially by enzymic hydrolysis. This results in the

formation of ammonia from acid amides; soy sauce contains ammonium complexes of amino acids, including ammonium glutamate.

The flavor of glutamate is difficult to describe. It has sometimes been suggested that glutamate has a meaty or chickeny taste, but it is now generally agreed that glutamate flavor is unique and has no similarity to meat. Pure sodium glutamate is detectable in concentrations as low as 0.03 percent; at 0.05 percent the taste is very strong and does not increase at higher concentrations. The taste has been described (Crocker 1948) as a mixture of the four tastes. At about 2 threshold

values of glutamate concentration, it could be well matched by a solution containing 0.6

threshold of sweet, 0.7 of salty, 0.3 of sour, and 0.9 of bitter. In addition, glutamate is said to cause a tingling feeling and a marked persistency of taste sensation. This feeling is present in the whole of the mouth and provides a feeling of satisfaction or fullness. Apparently glutamate stimulates our tactile sense as well as our taste receptors. The presence of salt is required to produce the glutamate effect. Glutamate taste is most effective in the pH range of 6 to 8 and

decreases at lower pH values. Sugar content also affects glutamate taste. The taste in a

complex food, therefore, depends on a complex interaction of sweet, sour, and salty, as well as the added glutamate.

Monosodium glutamate improves the flavor of many food products and is therefore widely used in processed foods. Products benefiting from the addition of glutamate include meat and poultry, soups, vegetables, and seafood. For many years glutamate was the only known flavor enhancer, but recently a number of compounds that act similarly have been discovered. The 5'-nucleotides, especially 5'-inosinate and 5'-guanylate, have enhancement properties and also show a synergistic

effect in the presence of glutamate. This synergistic effect has been demonstrated by determining the threshold levels of the compounds alone and in mixtures. The data in Table 7-9 are quoted from Kuninaka (1966). The 5'-nucleotides were discovered many years ago in Japan as components of dried bonito (a kind of fish). However, they were not produced commercially and used as flavor enhancers until recently, when technical problems in their production were solved.

The general structure of the nucleotides with flavor activity is presented in Figure 7-21.

There are three types of inosinic acid, 2'-, 3'-,and 5'-isomers; only the 5'-isomer has flavor

activity. Both riboside and S'-phosphomonoester linkages are required for flavor activity,

which is also the case for the OH group at the 6-position of the ring. Replacing the OH group with other groups, such as an amino group, sharply reduces flavor activity but this is not true for the group at the 2-position. Hydrogen at the 2-position corresponds with inosinate and an amino group with guanylate; both have comparable flavor activity, and the effect of the two compounds is additive. The synergistic effect of umami substances is exceptional. The subjective taste intensity of a blend of monosodium glutamate and disodium 5'-inosinate was found to be 16 times stronger than that of the glutamate by itself at the same total concentration (Yamaguchi

1979).