GENERAL INTRODUCTION

I. GENERAL INTRODUCTION

A. Definitions

A flavor enhancer is a substance that is added to a food to supplement or enhance its original taste or flavor. The term flavor potentiator has also been used with the same meaning.

The most commonly used substances in this category are monosodium L-glutamate (MSG), disodium 5 ′-inosinate (IMP), and disodium 5′-guanylate (GMP).

B. Historical Background

Dried seaweed for the preparation of soup stock was registered even in the oldest record on foods written on narrow strips of wood in the 8th century in Japan. The seaweed kombu (Laminaria japonica) has been an important item of trade from the northern islands to central Japan ever since. It became an offering for the divine service and a sacred gift at the formal engagement ceremony. Dried fermented bonito, katsuobushi, has also been used and was thought to be in the same category. (Kombu connotes delight, and katsuo- bushi connotes victory.)

Cooks around the world have known how to prepare good soup using vegetables and meat or bones from time immemorial. Ancient Romans loved Garme, fermented fish sauce. In Japan soups were prepared with the unique raw materials mentioned. This may

be the reason why Professor Kikunae Ikeda tried and succeeded in isolating the essence of ‘‘tastiness’’ of soup. In 1908, he isolated glutamic acid from kombu bouillon and named be the reason why Professor Kikunae Ikeda tried and succeeded in isolating the essence of ‘‘tastiness’’ of soup. In 1908, he isolated glutamic acid from kombu bouillon and named

Commercialization of glutamate began in 1909 with its isolation from wheat gluten. Today about 640,000 tons (Anonymous, 1993) of MSG are manufactured annually in some 14 countries throughout the world.

In 1913 the investigations of Ikeda’s protege Shintaro Kodama into dried bonito led to a second important realization: the discovery that inosinic acid, known since German scientist Justus Freiherr’s mid–19th century experiments on beef broth, was another typi- cal umami substance (Kodama, 1913).

Clarification of the full configuration of umami was not achieved until 1960, when Akira Kuninaka recognized the role of 5 ′-guanylate as another key component. The shii- take mushroom (Lentinus edodus) has been used as an invigorant. In 1960, guanylic acid— which in 1898 had been first introduced to the scientific community by British researcher Ivar Bang in his work on pancreatic nucleic acid—was extracted from the broth of the common shiitake mushroom (Kuninaka, 1960).

Many other flavor enhancers are reported and listed in Tables 6 and 7 . Ibotenic and tricholomic acids were isolated from the mushrooms Amanita strobiliforms and Tricho- loma muscarium , respectively. However, these two compounds are not commercially pro- duced.

C. Food Occurrence

It is important to note that both compounds comprising umami, that is, glutamate (salts of glutamic acid) and nucleotides, are key components of living organisms.

Glutamate is naturally present in virtually all foods, including meat, fish, poultry, milk (human milk), and many vegetables. It occurs in bound form when linked with other amino acids to form protein, and also in free form when it is not protein bound or in peptides.

Therefore, protein-rich foods such as human milk, cow’s milk, cheese, and meat contain large amounts of bound glutamate, while most vegetables contain little. De- spite their low protein content, many vegetables, including mushrooms, tomatoes, and peas, have high levels of free glutamate. The glutamate content in foods is shown in Table 1 .

It has been noted that glutamate is an important element in the natural and traditional ripening processes that allow the fullness of taste in food to be achieved. Perhaps this is why foods naturally high in glutamate, such as tomatoes, cheese, and mushrooms, have become important to the popular cuisines of the world.

Nucleotides are specifically distributed as shown in Tables 2 and 3 . Disodium 5 ′- inosinate (IMP) is dominant in meat, poultry, and fish, whereas adenosine monophosphate (AMP) is dominant in crustaceans and mollusks; furthermore, almost all vegetables con- tain AMP.

The GMP content of mushrooms is particularly high, especially in the shiitake spe- cies, which is a traditional cooking ingredient in Japan and China.

Table 1 Glutamate Content in Foods Protein

Glutamate

Protein-bound Free

glutamate glutamate Food

in food a in protein

(g/100 g) a (mg/100 g) Cow’s milk

2.9 19.3 0.560 1.9 b Human milk

1.1 15.5 0.170 22 b Camembert cheese

17.5 c 27.4 4.787 c 390 d Parmesan cheese

36.0 c 27.4 9.847 c 1400 e Cheddar cheese

5.092 f 1 month

21.8 g 8 months

182 g Gruyere

5.981 f Appenzel

460 e Beaufort

910 e Comte

630 e Blue cheese

5.189 f Roquefort

1230 e Eggs

12.8 12.5 1.600 23 h Chicken

22.9 16.1 3.700 44 i Beef

18.4 13.5 2.500 33 i Pork

20.3 15.7 3.200 23 i Green peas

7.4 14.8 1.100 75 j Sweet corn

3.3 15.1 0.500 100 k Tomato

0.7 37.1 0.260 246 k Tomato green

20.0 l red

143.3 l Canned tomato

0.343 m 202 n Tomato juce

0.303 m 109 n Tomato paste

1.510 m 556 n Onion

0.190 m 102 n Potato

0.347 m 180 n Broccoli

0.375 m 115 n Spinach

3.3 9.1 0.300 47 k a Resources Council, Science and Technology Agency, Japan (1986).

b Rassin et al. (1978). c The Glutamate Association. d Giacometti (1979). e Orsan (1993).

f USDA (1976). g Weaver (1978). h Maeda et al. (1961).

i Maeda et al. (1958). j Suzuki et al. (1976). k Kiuchi and Kondo (1984). l Inaba (1980). m USDA, (1984). n Skurray (1988).

Table 2 Distribution of Nucleotides in Animal Foods Nucleotides content (mg/100 g) Food

Horse mackerel

Sweet fish

Common sea bass

Black sea bream

Pike mackerel

Keta salmon

Globefish

Dried benito 630–1310

Common octopus

Spiny lobster

Hairy crab

Common abalone

Round clam

Common scallop

Short-neck clam

Source : Nakajima et al. (1961); Ohara et al. (1964); Saito (1961); Hashida (1963); Fujita and Hashimoto (1959).