- Email: [email protected]
Sensory and preference aspects of umami
15 16
17 18 19
Lareo,C., Tucker, G.S. and Fryer, P.J. EUROMECH307 Proc. (in press) Lenn,CP., Sanderson,M.L., Spence, L. and Richardson, P.S, (1989) Technical Memo 540, Campden Food and Drink ResearchAssociation, Chipping Campden, UK Dutla, B. and Sastry,S.K. (1990) I. FoodScL 55, 1448-1453 Hong,C.W., Sun Pan, B., Toledo, R.T. and Chiou, K.M. (1991) I. Food Sci. 56, 255-256, 259 Lee,J,H. and Singh, R.K.(1991) I. Food Sci. 56, 869-870
20 21 22 23 24
Yang,B.B. and Swarlzel, K.R. (lqql)]. FondSci. 56: 1076-1081, 1086 Alcairo,E.R.and Zuritz, C.A. (1990) Trans. ASAE 33, 1621-1628 Segner,W.P., Ragusa,T.I., Marcus, C.L. and Soutter, E.A. (1989) J. Food Prec. Pres. 13, 257-274 Tucker,G.S. and Withers, P.M. (1992) Technical Memo 667, Campden Food and Drink ResearchAssociation, Chipping Campden, UK Tucker,G.S., Lareo, C. and Fryer, P.J.EUROMECH 301 Prec. (in press)
Review
Sensoryand preference°V aspectsof umami
has been with us for centuries in the stocks or bouillons ~ of Europe, bcefteaand Worcestershire sauce in the UK, !! the pizzas and tomato sauces of Italy, the 'tan broth of ~'~ China and the fish sauces of Southeast Asia. The intensity of umami taste in foods is produced by the coexistence of glutamate and 5'-ribonucleotides such as 5'-inosinate or 5'-guanylate, which have a synergistic taste effect. The taste produced by these substances is definitely different from the so-called four 'basic tastes': Glutamic acid was first identified as the essence of 'tastiness' sweet, sour, salty and bitter. Umami taste, produced by the mixture of glutamate and nucleotides, is further in a Japanese seaweed stock in 1908, and its characteristic enhanced by sulfur-containing substances isolated from taste was named 'umami'. The umami taste appears to be garlic4, which is widely used in Italian, French, Korean independent of the four traditional 'basic' tastes, and plays a and other dishes. major role in the acceptability of many foods; when low levels of umami substances are added to foods, salt levels can Food and its taste components Amino acids and 5'-ribonucleotides be reduced wilhout affecting palatability. Nutritional studies The tastes of amino acids have traditionally been repin rats suggest that a preference for the umami taste is a resented by one dominant basic taste, such as sweet marker of adequate protein intake. (Ala, Gly, Pro, Ser, etc.), bitter (Arg, Phe, His, Val, Trp, etc.) or sour (Glu and Asp)"~. The sodium salts of Glu and Asp elicit the umami taste, so they have been classified as umami amino acids". Glu is naturally present in Umami is defined as the taste of monosodium glutamate virtually all foods. Several groups have reported the free (MSG) and 5'-ribonucleotides such as sodium salts of Glu contents of various foods (expressed below as mg 5'-inosine monophosphate (IMP) and 5'-guanosine per 100g of food), such as meats (chicken, 44rag; monophosphate (GMP), which are widely used as flavor beef, 33mg, pork, 23rag) 7, cheeses (Parmesan, enhancers to improve the taste of foods throughout the 1200rag; Gruy6re de Comte, 1050rag; Camembert, world. 390 mg)s and vegetables (e.g. tomato, 292 mg; potato, in 19(18, Dr K. ikeda isolated glutamic acid as the 180mg; broccoli, 115 mg)'L Human breast milk is also essence of 'tastiness' in the Japanese stock prepared rich in Giu (22 mg), with more than ten times the Glu from konbu seaweed, and he named its distinct taste content of cow's milk (I.9 rag)'". "umami". In 1913, Ikeda's prot6g6, S. Kodama, isolated Among the 5'-ribonucleotides, IMP, 5'-adenosine 5'-inosinic acid from dried skipjack as another key com- monophosphate (AMP) and GMP contribute to the ponent of the stock:. In 1960, A. Kuninaka isolated umami taste in natural foods. IMP is dominant in meats 5'-guanylate and recognized its role in the broth of dried (chicken, ll5mg; beef, 163rag; pork, 186mg)and shiitake mushroom". Although these umami substances fish (tuna, 286mg: salmon, 154mg), whereas AMP is happened to be discovered as important taste com- dominant in shellfish or molluscs (scallop, l l6mg; ponents by three Japanese scientists, the umami taste squid, 184rag; lobster, 82mg)'L GMP is generally abundant in mushroom species. Dried shiitake mushShinyaFuEeis at lhe Facultyof Education,TokyoGakugeiUniversity, Nukui- room is often used for Chinese and Japanese stocks and kilama(hi 4-1.1, Koganei, Tokyo 184, lal)an. Telsuji Shimizu is with lhe dishes. The GMP content of dried shiitake (156.5mg) h)od Researchand Development Laboratories,Ajinomolo Co., Inc., 1-1 is three times greater than that of fresh shiitake Suzuki-Cho,Kawasaki-ku,Kawasaki210, Japan. ( 16-45 mg)':.
ShinyaFukeand TetsujiShimizu !!
24h
,,,n,J,~~.t,,,,,,., ,,,,,,,,,,I',,I,ti,h,.r,0t,i.~(7~, ,,24 -.'.tq4/,p~/$.,,.,,.
Trends in Food Science & Technology August 1993 lVol. 41
.
Synergistic taste effects The tastes of foods are usually made up of the sum of the several taste components in the foods. Moreover, certain taste components have a taste-enhancing effect. For example, NaC! has been shown to enhance the sweet taste of Aia in an electrophysiological study of dog chorda tympani nerve ~3. When both glutamate and a 5'-ribonucleotide coexist in a food, the umami taste of the food increases by more than the sum of the umami taste intensities of glutamate and the 5'-ribonucleotide. This taste enhancement is called a synergistic effect 14. Figure ! demonstrates the typical synergistic effect between MSG and IMP. in the case of MSG alone, the taste intensity increases linearly with concentration, but the taste intensity of the mixture of MSG and IMP increases exponentially. This synergistic taste effect has also been recognized in various soups prepared from seafoods, meats, cereals, beans and vegetables L~. The levels of MSG or IMP in the soups were all lower than their threshold taste concentrations, but the umami taste of the soups was increased by adding less than the threshold amount of MSG or IMP. Although the synergistic effect between AMP and MSG is one fifth as strong as the effect between IMP and MSG, AMP strongly enhances the sweetness of boiled prawn'. Succinic acid, recognized as one of, the taste components in short-necked clam and hard clam, has no synergistic taste effect with IMP ~7. A synergistic taste effect has also been detected among three taste components (ct-amino acids, a mixture of IMP and GMP, and Asp or Glu) in a !~, NaCI solution ~'~.However, no synergistic effect was recognized between (t-amino acids and Asp or Glu, or between (t-amino acids (other than Asp and Glu) and the nucleotide mixture. The synergistic effect was observed among Ala, Cys, Gly, His.HCI, Pro, Ser, Thr, Tyr and Val. Although the tastes of amino acids were different from each other, the taste imparted by this synergism was the same.
Umami and basic tastes Until recently, it was assumed that there are only four basic tastes: sweet, sour, salty and bitter. The theory of four basic tastes was originally proposed by a German psychologisP", who proposed the psychological explanation that the four basic tastes were located at the corners of a tetrahedron. All tastes experienced could be made up from mixtures of the four basic tastes, and were located somewhere on the surface of the tetrahedron. This theory was accepted for a long time without sufficient scientific data to support it. Recent psychometric, biochemical and neuroelectrophysiological studies indicate the following: • as demonstrated by multidimensional scaling analysis
of human sensory tests, the umami taste is located outside the tetrahedron of the traditional four basic tastes, and the taste quality is distinctly different from those of the other basic tastes:"'2~; Trends in Food Science & Technology August 1993 IVol. 4]
i
¢~
"
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
I
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
t=4o/.
I o.s
.
I
"--"
/ -
t=2%
/
1 / / / //
,ooj / / / / l u 0I
Concentration of MSG-IMP mixture (g/dl) Fig. 1 Relationship between the taste intensitiesof MSGalone and mixtures of MSG and IMP (t is the proportion of IMP in the mixture). Points on the curves corm'late the concentrations of MSG alone and of the MSG-IMP mixtures giving an equivalent taste intensity. Adapted from Ref. 14. • the taste quality of umami is not produced by mixing
any of the other four basic tastes-'": • the taste bud receptor site for glutamate is different
from those for the traditional four basic tastes -'-''-'3. The most recent electrophysiological studies in primates and histological studies in rodents suggest that specific gustatory cells are responsible for the taste stimuli of umami substances such as MSG and GMP, and that there is a single taste nerve in the chorda tympani and a secondary taste cortex in the brain that are specifically activated by umami taste stimuli -'4--''. in this sense, it could be said that umami is a basic taste, independent of the four traditional basic tastes. The acceptability of foods is decided by many factors, such as taste, smell, color, temperature and overall appearance, as well as by physiological or mental conditions (Fig. 2). Among these factors, the most
SweetneSs~ Sourness Saltiness Bitternes
~
Umami m m m m Spicy taste , ~ =
1
Metallic taste ~ - Astringent taste == Amplitude tomb Continuity ~ , Aroma Texture ~ , Temperature Color ShaDe m Personal condition (mood & healtl~) Other factors ~ m r (environment, habituation, social situation,culture)
Fig. 2 Umami and other factors involved in food acceptability.
247
Table 1~-Taste-active ................................................................................... ocm sponet in seafoods(mg/100 gP'u Short-necked
Component
Abalone Seaurchin Snowcrab Scallop
clam
Glu Gly Ala Val
109 174 98 37
103 842 261 154
19 623 187 30
140 1925 256 8
90 180 74 4
Met Arg Tau
13 299 946
47 316 105
19 579 243
3 323
3 53 555
AMP IMP
90 ND ND 975 ND
10 2
32
2
-
-
K+
-
-
4 357 9 191 197
10 73 218
CI PO4)-
-
-
336
95
-
-
217
213
GMP Bet Suc Na•
7 1.2
5
784 172 ND ND
339
28 ND ND 42 65 244
273 322 74
aTaste.activecomponentsare indicatedin boldtype bAdaptedfromRef.30 ND, Not detected;-, not analysed Bet,Glycinebetaine;Suc,succinicacid;Tau,taurine
important direct factors are the basic tastes of sweet, sour, salty, bitter and umami. During the past two decades, a number of studies have investigated the umami taste from various perspectives: food science, biochemistry, psychophysics, neurophysiology, physiology, nutrition, etc. The results of many of these interdisciplinary studies were presented at two international symposia on umami: one was held in Kauai, Hawaii in 1985 and the other in Sicily, Italy in 1990. The proceedings of both of these symposia have been published (see Retg 27 and 28, respectively). Role of umami components in the taste of foods
Seafoods Foods are usually extracted by ethanol or hot water in order to analyse their taste components, in the case of seafoods, more than 90% of extracted nitrogen compounds can be accounted for by free and combined amino acids, nucleotides and related substances, organic bases, trimethylamine and trimethylamine oxides, ereatine and creatinine, and betaines. Non-nitrogenous compounds such as sugars and organic acids are also listed
as taste components -''),~". A synthetic extract can be prepared by mixing the various chemical components according to their known ratios in the food and adjusting the pH to that of the natural extract. The synthetic extract thus prepared usually reproduces well the taste of the natural extracP )..~:. To investigate the role of each component in a food, an omission test is often used. In an omission test, synthetic extracts with and without one or a group of components are prepared. The differences between pairs of extracts are then evaluated by the triangle difference test or paired difference test. Taste panelists are asked to determine differences between the two synthetic extracts and to evaluate the differences using five-point rating scales for specific taste components (i.e. sweet248
ness, sourness, saltiness, bitterness and umami) and flavor characteristics (e.g. complexity, thickness, overall preference). The results are analysed statistically and the taste-active components are disclosed. When the significance of each taste component was assessed in seafoods, umami compounds were found to be crucial in determining the distinctive taste of each type of seafood-". Table 1 shows the results of omission taste tests using synthetic extracts of seafoods 3". Both Glu and Gly were taste active in all five kinds of seafoods studied, irrespective of their levels. Furthermore, Glu in synthetic extracts not only elicited umami taste but also improved overall preference as a result of imparting continuity, thickness, complexity and mildness. An elevation of sweetness by Glu was recognized in all the synthetic extracts except for sea urchin, in which the extract without Glu was sweeter than that with Giu -~. Giy imparted sweetness in all the synthetic extracts. Ala was taste active only in sea urchin, snow crab and scallop 3", in which its level was relatively high. Arg was taste active in snow crab, scallop and short-necked clam. Although Arg is a bitter amino acid, it contributed to enhancing overall preferences such as continuity, thickness, complexity and mildness. Sodium and chloride ions are also important in producing the tastes of snow crab, scallop and short-necked clam. The common feature of synthetic extracts lacking Na ÷ was a remarkable decrease in sweetness, umami and characteristic overall flavor, and an increase in bitterness. Omission of CI- caused a dramatic change in the extract, creating an almost tasteless solution. The potassium ion was also taste active in the same three seafoods. Omission of K ÷ made the synthetic solutions watery, but the solutions retained a little umami and characteristic overall flavor. The phosphate ion was taste active only in snow crab. Its omission from the synthetic extract decreased saltiness, sweetness and umami. Thus, the taste-active components of the seafoods listed in Table 1 resembled each other even though the overall tastes of each of the seafoods were different. This suggests that not only the combinations of tasteactive components but also their relative amounts are important to produce the characteristic flavor of each seafood. Although the Glu content in snow crab extract is rather low compared with levels in the other seafoods, Glu makes a remarkable contribution to the distinct flavor characteristics of snow crab. Meats The extractive components of aged beef, pork and chicken have been analysed and the tastes of synthetic extracts consisting of free amino acids, IMP and NaCI have been evaluated -'7. Synthetic extracts containing free amino acids, including Glu, in addition to IMP and NaCI reproduced well the intensity of brothy, umami and salty tastes of natural soups. Thus, free amino acids and IMP contributed to the brothy and umami tastes of the meats. Trends in Food Science& TechnologyAugust 1993 lVol. 41
Evaluationscore Added MSG (0.2%, w/w)
Aroma/flavor characteristic
Tomatoes The contents of free amino acids, sugars and organic acids, which are dependent mostly on the ripeness and species, are related to the taste of tomatoes 34.35. Synthetic extracts have been prepared containing citric acid (4g), glucose (35g), KH2PO 4 (0.31 g), MgSO4-7H_,O (0.25g) and CaCi2"2H20 (0.22g) in l litre of watera*. Glu and Asp were added to the extracts in various proportions. Sensory tests showed that when the weight ratio of Glu (2.8 g) to Asp (0.7 g) was 4 in the synthetic extract, the taste was very similar to that of tomato. The appropriate ratio of Glu to Asp and the coexistence of both components were the most important factors in reproducing tomato flavor (Table 2). Citric acid was preferable to other organic acids such as lactic, malic and tartaric acids. AMP is the dominant nucleotide in tomato -~4,but the role of AMP as well as the synergistic effect between Glu and AMP are yet to be investigated.
Potatoes Free amino acids and 5'-nucleotides are known to contribute to the taste of potato. Raw potatoes contain only very small amounts of 5'-nucleotides, but the enzymatic hydrolysis of ribonucleic acids (RNA) in the potatoes during heat processing produces 5'-nucleotides in boiled potatoes. Boiled potatoes contain AMP (3mg/100g raw potato) and GMP (2.11 mg/100g raw potato). Taste tests using a synthetic mixture have shown that Glu (73.8mg/100g raw potato), Asp (46.8mg/100g raw potato) and 5'-nucleotides are consistently important in conveying an agreeable potato taste, though different potato species have different taste characters ~7.
Aroma
-1 '
Overall aroma Meaty
0 | :
~
Double-concentrated beef broth 0 +1 +2
+1 ' ;
I
'
!
I
Vegetable-like Acceptability
'
: -" "
_ ~L L " [
Basic taste
Overall taste
/
Satty
~
Sweet Sour Bitter
~ ~l .
" : :
:
.
~
-
:
- ]
Flavor characteristic
Continuity Mouthfulness Impact
|
. : : I : : • : : •
I I
Mildness
~
Thickness
I
.
. :
:
1
:
./1.~
Other flavor Spicy
Oily Meaty Vegetable-like
. I,i ~
Overall preference
l
--.-,=i,.4
Palatability I -1
0
+1
0
I
I
+1
+2
Fig. 3 Effectsof adding MSGand doubling the concentraliion of beef broth on the flavor profileof beefconsomme. A score of 0 indicates no effect; a positive score indicates an enhancement and a negative score a reduction in a given aroma/flavor characteristic. Adapted from Ref. 12.
Umami in broth
0
280
0
Similar in sweetness and sourness
280
0
-
Increase in umami; not similar
280
5.6
50
Taste flat; not similar
14
20
Good similarity
280
70
4
Best similarity; taste balance good
280
280
1
Good similarity
The function of umarni in dishes has been confirmed by sensor), evaluation ~:. Figure 3 shows the effects of added MSG on the flavor profile of beef consomm6. Added MSG had no effect on aroma but increased the overall taste intensity, while sweetness, sourness, saltiness and bitterness did not significantly increase. The addition of MSG also increased flavor characteristics such as continuity, 'mouthfulness', impact, mildness and thickness. Meaty flavor and the overall preference also increased. Doubling the concentration of beef broth in consomm6 gave a similar overall pattern of change in the flavor profile as the addition of MSG, and in addition increased the intensity of aromas and the four basic tastes.
280
560
0.5
Similar, but sourness strong
Sodium intake reduction
280
1120
0.25
Not similar and very i strong sourness t
Glu Asp (mg/lO0 ml) (mg/lO0 ml)
280
Similarity to natural extract
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
'~AdaptedfromRef.36 ...................................................................
Trends in Food Science & Technology August 1993 [Vol. 4]
:
:
/
Table L Effect on taste of the Glu: Asp ratio in synthetic tomato extracts a Weight ratio (Glu : Asp)
_.
: .
The umami taste itself is not palatable in its water solution, but it does convey palatability and improve taste when applied to food systems. Sensory tests in humans have shown that as the NaC! level in a food is ! reduced, acceptability of the food decreases. However, J
249
when a small amount of MSG is added, NaC! intake can be reduced without changing the acceptability of the food, in Japanese clear soup, levels of O.81% NaC! and 0,38% MSG gave optimal palatability ~s. The optimal NaCI concentration without using MSG was 0.92%. Thus, salt intake was reduced by 12% by using MSG in Japanese clear soup. MSG has also been reported to improve the palatability of an NaCl-restricted diet served in a hospital in Korea 3".
ology and the regulatory mechanism of umami preference are being presented in the l lth International Symposium on Oifaction and Taste (ISOT XI) held in Sapporo, Japan in July 1993. Another symposium, on 'umami taste and food intake', is being held at the 1 lth International Conference on the Physiology of Food and Fluid Intake (ICPFF! 11) in Oxford, UK in July 1993, covering the effects of umami on human appetite and the mechanism of umami preference.
Preference for umami
Acknowledgement
Nutritional
studies have s h o w n that the p r e f e r e n c e o f
rats for the umami taste is altered by changes in protein nutritional status, either a change in total protein intake or an alteration of the amino acid balance in the diet. Rats in a state of protein deficiency preferred NaC! and Gly solutions over umami (MSG or a mixture of MSG and GMP) solutions. A preference for NaC! may maintain electrolyte and body fluid balances. When the diet contained sufficient protein, rats preferred the umami solutions. Another study showed that rats have the ability to select a diet with a balanced amino acid content. When a Lys-deficient diet was offered, rats were able to distinguish a Lys solution from 15 other amino acids in solution. Once the amino acid balance in the diet was improved by the intake of a Lys solution, a preference for the umami solutions appeared ~". This means that a preference for the umami taste was induced when the level of dietary protein was within the normal range, but that a preference for NaCI was induced in a state of marginal protein deficiency. The regulatory mechanisms for this change of preference are currently being studied by behavioral and neurophysiological approaches. A recent study suggests that umami taste perception plays an important role in protein metabolism and in maintaining amino acid homeostasis within normal limits4~.
Conclusions Umami is the characteristic taste of glutamate and 5'-nucleotides. Psychophysical and electrophysiological studies indicate that umami is a taste sensation independent of the four basic tastes of sweet, sour, salty and bitter. Nutritional studies in rats suggest that a preference for the umami taste may be a taste marker for adequate protein intake.
Umami plays a major role in improving the palatability and acceptability of many foods. This could explain why tbods containing high levels of umami substances, such as tomato, cheese, fish sauces, etc., are often used for their flavorful qualities. When low levels of umami substances are added to a food, NaCI levels can be reduced without changing the palatability. 'Healthy eating' is a hot issue in many countries, and many people have a great interest in reducing their daily sodium intake. The salt-reduction effect of umami substances could be used to make a low-sodium diet more palatable. The most advanced researches on umami in the fields of food science, psychophysics, neurophysiology, physi250
We thank Mrs K. Ninomiya, of The Umami Manufacturers" Association of Japan, for kind assistance.
References 1 2 3 4 5 6 7 II
Ikeda, K. c! 9091 J. Tok~,'oChem. 5oc. 30, 820-8 36 Kodama,S. (19 ! 3 ~I. Tokyo Chem. 5oc. 24, 751-75 3 Kuninaka, A. ~1911(]!I. Agric. Chen~. Soc. lapan .34,487-4q2 Ueda, Y., Saka~,uchi, M., Hirayama, K.. Miyajima, R. and Kimizuka, A. ( l qqO) Agric. Biol. Chem. 54, 1613-16() Birch, G.G. and Keml), S.E. l lqBC)) Chem. Senses 14, 249-258 Kato, H. t1987)in UmamilKawamura, Y. and Kimura, S., eds), pp. 175-201, Eidai Sehsho, Tokyo, Japan Maeda, S., Eguchi, S. and Sasaki, H. (1958) I. Home Econ. Ilapam 9, 163-167 Giacometti, T. ~107c)~in Glutamic Acid: Advances in Biochemistry and Physiology IFiler,L.I.,Jr, Garatlini,S., Kare,M.R.,Reynolds,W.A.and
Wurtman,R.I.,edsJ. t)P. 25-]4. RavenPress Skurray,G.R.and Pucar, N. (1988)Food Chem. 27. 177-180 10 Rassin,E.R.,Sturma,I.A.and Gaull,G.E. tlC]78)Earh' HumanDe~. 2. 1-1 II Ma~a, I.A.I198It CRC (Trit. Rel . Food Sc i. Ntttr. 18~13L 2 ] I-312 12 Komata,Y. (Iq86~C)i~hi,~ato Ali~,l~a./tic)K,~gaktt, NikkanKogyo Shinhun,lapan 9
13 Ul4awa, T. and Kurihara, K. Am. I. Physiol. fin IIress~ 14 Yamagu(hi. ft. and Kimizuka, A. ~It)TCl~in C;h&tmi( Acid: Ad~ ante.~ in
15 15
l~iochemL~tr~and lqwsic)lo,t~r IFiler, L.I.. It, Garatlini. S.. Kate. M.R., Revmd(Is, W.A. antl Wurlman. R.I,, eds). lip. 35-54. Raven Pre~s Ikecla, S. l lqbSl Neu Food Ind. 7t12L 41-46 Fake, S. and Watanabe,K. (It)~]21in Um,imi Forum IqO2
IKawamura,Y,, ed.I, p. 5, Socielvfor Researchon UmamiTaste, Tokyo, lal)an Furukawa,H. (1qc]I I Nippon Nogeik,lgaku kaishi 65, 1(13-16q Yokotsuka,T., Sailo,N., Okuhara,A, and Tanaka,K. ~1q691Nippon No,v,eikagaku Kaishi 413,165-17(] I-lenning,H. II91O)Z. Pslz'hol. 74, 20J-21t) Yanlaguchi,S. I1()871ill Umami: A Basic Taste IKawamura,Y. and Kare,M.R.,edsL Pl).41-713,MarcelDekker Ninomiya,Y.and Funakoshi,M. (1987)illUmami: A BasicTaste (Kawamura,Y. and Kare,M.R.,etls),pp. 365-1385,MarcelDekker 22 Ohno, T., Yoshii,K. and Kurihara,K. 119841Bn~in Res. 1310,13-22 23 Kumazawa,T., Nomura,T. and Kurihara.K.~1t1881Bk~c'hemistn'27, 123t) 24 Yoshie,S., Wakasugi,C., Teraki,Y., Kanazawa,H., Iwanaga,T. and Fujita, T. I I qgl) Physiol. Behav. 4t), 887-880 Hellekanl, G. and Ninomiya, Y. (Iqqll PhysioL Beha~,.4q, g27-q34 26 Bavlis, L.L, and Roils, E.T. Ilqqll Physiol. Beha~. 4~1,~)73-~)7q 27 Kawamura, Y. and Kare, M.R., edsll c)871 Umami: A Basic Tasle, Marcel Dekker 28 Kawamura, Y., Kurihara, K., Nicolaidis, S., Oomura, Y. and Wayner, M.I, (lt)91) Plwsiol. Behav. 49(5)ISpecial Issue: Umami, Proceedings of the Second International Symposium on Umamil, PergamonPress 29 Watanabe, K,, Lan, H.L.,Yamaguchi,K.and Konosu,S. (19901Nihon Shokuhin Kogvo Gakkaishi 37, 439-445
Trends in Food Science & Technology August 1993 IVol. 41
30 31 32 33 34 35 36
Fuke,S. and Konosu, S. (1991) Physiol. Behav. 49, 863-868 Komala,Y. (1964) Nippon Suisan Gakkaishi 30, 749-756 Hayashi,T., Yamaguchi,K. and Konosu,S. (1981) I. Food Sci. 46, 479-483,493 Watanabe,K. and Konosu,S. (1987)in Umami(Kawamura, Y. and Kimura, S., eds), pp. 140-171, Eidai Sensho,Tokyo, lapan Inaba,A., Yamamoto,T., Ito, T. and Nakamura,R. ~1980)I, Ipn. Soc. Holt. Sci. 49, 425-441 Kader,A.A., Stevens,M.A., Albright, M. and Morris, I_.L.(1978) I. Am. Soc. Hort. Sci. 103,541-544 Okumura,S., Eguchi, S., Ogawa, W. and Suzuki, K. (1968)lapanese Patent Publication (Kokoku) No. 43-11731
37 Solms,I. and Wyler,R.(1979)in FoodTasteChemistrytAmerican ChemicalSocielySymposiumSeries115;,pp. 175-184,American ChemicalSociety 38 Yamaguchi,S. and Takahashi,C. (1984)Agric.Biol.Chem.48, 1077-1081 39 Kimura,S., Kim,C.H.,Otomo,M.I.,Yokomukai,Y., Komai,M.and Morimatsu,F. (1990)in Abstractof the SecondInternational Symposiumon Umami(Kawamura,Y.,ed.), pp. 52-53, Societyfor 40
41
Researchon Umami Taste,Tokyo, Japan Torii, K., Mimura, T. and Yugari,Y. i1987) in Umami: A Basic Taste (Kawamura,Y. and Kare,M.R., eds), pp. 513-563, Marcel Dekker Tabuchi,E., Ono, T., Hishijo, H. and Torii, K. (1991) Physiol. Behav. 49, 951-964
Review
:i Fungal starter cultures Mould-fermented foods are produced with the help of fungal starter cultures, which are added to the foods as spore suspensions to ensure predictable fermentation results. Most
!!
fungal strains used today are screened and isolated from the native pool of organisms found in the food habitat. These strains do not always meet the requirements of modern food production. Few strains are toxicologically unobjectionable,
for fermented foods: molecular aspects
!i
and methods for developing new strains with new characteristics would be advantageous. This article discusses the cur-
ii Rolf Geisen
rent status of gene technology methods to improve fungal starter cultures for the production of mould4ermented foods.
An isolated strain for use as a starter culture should fulfil several requirements: • it should not be toxinogenic:
Mould-fermented foods play an important role in the human diet, especially in Asian countries. Shoyu, miso, katsuobushi, tempeh, sufu, oncom and ankak are just some of the Asian fermented foods produced by strains from the genera Aspergillus, Rhizopus, Actinomucor, Neurospora and Monascus'. Within the European market a limited number of mould-fermented foods are produced. Only a few fungal species are used for the production of these foods, all belonging to the genus Penicillium: P. camemberti for the production of white cheeses (Brie and Camembert), P. roqueforti for the production of blue cheeses (Roquefort, Gorgonzola, Stilton and Gammelost), and P. nalgiovense and P. cluysogenum for the production of meat products (salami-type sausages). Fungal starter cultures contribute to a large extent to the flavour and texture of the fermented food due to the action of various exoenzymes ~. Excreted proteases produce flavour-active peptides and amino acidsL Lipases produce free fatty acids, which can be converted to methyl ketones, alcohols or aldehydes, important for flavour formation 4. Rolf Geisen is at the Federal Research Centre for Nutrition, Institute of
Hygiene and Toxicology, Engesserstr.20, 76131 Karlsruhe,Germany. Trends in Food Science & Technology August 1993 IVol. 41
• it should not produce an antibiotic: • it should be adapted to the food product: • it should produce the appropriate amounts of proteases and lipases: • it should be antagonistic against pathogenic or spoilage bacteria characteristic of the fermented product: • iit should not produce any off-flavours. By far, most naturally isolated strains do not cover all of these requirements. However, using gene technology methods it should be possible to improve the characteristics of these strains.
Benefits of gene technological modification of fungal starter cultures Due to the ability of most Penicillium spp. to produce mycotoxins -~, only a limited number of strains arc available that are nontoxinogenic and can be regarded as GRAS ('generally recognized as safe'). Fungal starter cultures should not produce any mycotoxin or antibiotic. However, these requirements are not fulfilled even by currently used strains. All strains of P. camemberti ©1,),~L FlsvvierS(it.me Publishers Lid.dJKt (~q24-2244")I.'$(1(,.(111
251
17 18 19
Lareo,C., Tucker, G.S. and Fryer, P.J. EUROMECH307 Proc. (in press) Lenn,CP., Sanderson,M.L., Spence, L. and Richardson, P.S, (1989) Technical Memo 540, Campden Food and Drink ResearchAssociation, Chipping Campden, UK Dutla, B. and Sastry,S.K. (1990) I. FoodScL 55, 1448-1453 Hong,C.W., Sun Pan, B., Toledo, R.T. and Chiou, K.M. (1991) I. Food Sci. 56, 255-256, 259 Lee,J,H. and Singh, R.K.(1991) I. Food Sci. 56, 869-870
20 21 22 23 24
Yang,B.B. and Swarlzel, K.R. (lqql)]. FondSci. 56: 1076-1081, 1086 Alcairo,E.R.and Zuritz, C.A. (1990) Trans. ASAE 33, 1621-1628 Segner,W.P., Ragusa,T.I., Marcus, C.L. and Soutter, E.A. (1989) J. Food Prec. Pres. 13, 257-274 Tucker,G.S. and Withers, P.M. (1992) Technical Memo 667, Campden Food and Drink ResearchAssociation, Chipping Campden, UK Tucker,G.S., Lareo, C. and Fryer, P.J.EUROMECH 301 Prec. (in press)
Review
Sensoryand preference°V aspectsof umami
has been with us for centuries in the stocks or bouillons ~ of Europe, bcefteaand Worcestershire sauce in the UK, !! the pizzas and tomato sauces of Italy, the 'tan broth of ~'~ China and the fish sauces of Southeast Asia. The intensity of umami taste in foods is produced by the coexistence of glutamate and 5'-ribonucleotides such as 5'-inosinate or 5'-guanylate, which have a synergistic taste effect. The taste produced by these substances is definitely different from the so-called four 'basic tastes': Glutamic acid was first identified as the essence of 'tastiness' sweet, sour, salty and bitter. Umami taste, produced by the mixture of glutamate and nucleotides, is further in a Japanese seaweed stock in 1908, and its characteristic enhanced by sulfur-containing substances isolated from taste was named 'umami'. The umami taste appears to be garlic4, which is widely used in Italian, French, Korean independent of the four traditional 'basic' tastes, and plays a and other dishes. major role in the acceptability of many foods; when low levels of umami substances are added to foods, salt levels can Food and its taste components Amino acids and 5'-ribonucleotides be reduced wilhout affecting palatability. Nutritional studies The tastes of amino acids have traditionally been repin rats suggest that a preference for the umami taste is a resented by one dominant basic taste, such as sweet marker of adequate protein intake. (Ala, Gly, Pro, Ser, etc.), bitter (Arg, Phe, His, Val, Trp, etc.) or sour (Glu and Asp)"~. The sodium salts of Glu and Asp elicit the umami taste, so they have been classified as umami amino acids". Glu is naturally present in Umami is defined as the taste of monosodium glutamate virtually all foods. Several groups have reported the free (MSG) and 5'-ribonucleotides such as sodium salts of Glu contents of various foods (expressed below as mg 5'-inosine monophosphate (IMP) and 5'-guanosine per 100g of food), such as meats (chicken, 44rag; monophosphate (GMP), which are widely used as flavor beef, 33mg, pork, 23rag) 7, cheeses (Parmesan, enhancers to improve the taste of foods throughout the 1200rag; Gruy6re de Comte, 1050rag; Camembert, world. 390 mg)s and vegetables (e.g. tomato, 292 mg; potato, in 19(18, Dr K. ikeda isolated glutamic acid as the 180mg; broccoli, 115 mg)'L Human breast milk is also essence of 'tastiness' in the Japanese stock prepared rich in Giu (22 mg), with more than ten times the Glu from konbu seaweed, and he named its distinct taste content of cow's milk (I.9 rag)'". "umami". In 1913, Ikeda's prot6g6, S. Kodama, isolated Among the 5'-ribonucleotides, IMP, 5'-adenosine 5'-inosinic acid from dried skipjack as another key com- monophosphate (AMP) and GMP contribute to the ponent of the stock:. In 1960, A. Kuninaka isolated umami taste in natural foods. IMP is dominant in meats 5'-guanylate and recognized its role in the broth of dried (chicken, ll5mg; beef, 163rag; pork, 186mg)and shiitake mushroom". Although these umami substances fish (tuna, 286mg: salmon, 154mg), whereas AMP is happened to be discovered as important taste com- dominant in shellfish or molluscs (scallop, l l6mg; ponents by three Japanese scientists, the umami taste squid, 184rag; lobster, 82mg)'L GMP is generally abundant in mushroom species. Dried shiitake mushShinyaFuEeis at lhe Facultyof Education,TokyoGakugeiUniversity, Nukui- room is often used for Chinese and Japanese stocks and kilama(hi 4-1.1, Koganei, Tokyo 184, lal)an. Telsuji Shimizu is with lhe dishes. The GMP content of dried shiitake (156.5mg) h)od Researchand Development Laboratories,Ajinomolo Co., Inc., 1-1 is three times greater than that of fresh shiitake Suzuki-Cho,Kawasaki-ku,Kawasaki210, Japan. ( 16-45 mg)':.
ShinyaFukeand TetsujiShimizu !!
24h
,,,n,J,~~.t,,,,,,., ,,,,,,,,,,I',,I,ti,h,.r,0t,i.~(7~, ,,24 -.'.tq4/,p~/$.,,.,,.
Trends in Food Science & Technology August 1993 lVol. 41
.
Synergistic taste effects The tastes of foods are usually made up of the sum of the several taste components in the foods. Moreover, certain taste components have a taste-enhancing effect. For example, NaC! has been shown to enhance the sweet taste of Aia in an electrophysiological study of dog chorda tympani nerve ~3. When both glutamate and a 5'-ribonucleotide coexist in a food, the umami taste of the food increases by more than the sum of the umami taste intensities of glutamate and the 5'-ribonucleotide. This taste enhancement is called a synergistic effect 14. Figure ! demonstrates the typical synergistic effect between MSG and IMP. in the case of MSG alone, the taste intensity increases linearly with concentration, but the taste intensity of the mixture of MSG and IMP increases exponentially. This synergistic taste effect has also been recognized in various soups prepared from seafoods, meats, cereals, beans and vegetables L~. The levels of MSG or IMP in the soups were all lower than their threshold taste concentrations, but the umami taste of the soups was increased by adding less than the threshold amount of MSG or IMP. Although the synergistic effect between AMP and MSG is one fifth as strong as the effect between IMP and MSG, AMP strongly enhances the sweetness of boiled prawn'. Succinic acid, recognized as one of, the taste components in short-necked clam and hard clam, has no synergistic taste effect with IMP ~7. A synergistic taste effect has also been detected among three taste components (ct-amino acids, a mixture of IMP and GMP, and Asp or Glu) in a !~, NaCI solution ~'~.However, no synergistic effect was recognized between (t-amino acids and Asp or Glu, or between (t-amino acids (other than Asp and Glu) and the nucleotide mixture. The synergistic effect was observed among Ala, Cys, Gly, His.HCI, Pro, Ser, Thr, Tyr and Val. Although the tastes of amino acids were different from each other, the taste imparted by this synergism was the same.
Umami and basic tastes Until recently, it was assumed that there are only four basic tastes: sweet, sour, salty and bitter. The theory of four basic tastes was originally proposed by a German psychologisP", who proposed the psychological explanation that the four basic tastes were located at the corners of a tetrahedron. All tastes experienced could be made up from mixtures of the four basic tastes, and were located somewhere on the surface of the tetrahedron. This theory was accepted for a long time without sufficient scientific data to support it. Recent psychometric, biochemical and neuroelectrophysiological studies indicate the following: • as demonstrated by multidimensional scaling analysis
of human sensory tests, the umami taste is located outside the tetrahedron of the traditional four basic tastes, and the taste quality is distinctly different from those of the other basic tastes:"'2~; Trends in Food Science & Technology August 1993 IVol. 4]
i
¢~
"
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
I
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
t=4o/.
I o.s
.
I
"--"
/ -
t=2%
/
1 / / / //
,ooj / / / / l u 0I
Concentration of MSG-IMP mixture (g/dl) Fig. 1 Relationship between the taste intensitiesof MSGalone and mixtures of MSG and IMP (t is the proportion of IMP in the mixture). Points on the curves corm'late the concentrations of MSG alone and of the MSG-IMP mixtures giving an equivalent taste intensity. Adapted from Ref. 14. • the taste quality of umami is not produced by mixing
any of the other four basic tastes-'": • the taste bud receptor site for glutamate is different
from those for the traditional four basic tastes -'-''-'3. The most recent electrophysiological studies in primates and histological studies in rodents suggest that specific gustatory cells are responsible for the taste stimuli of umami substances such as MSG and GMP, and that there is a single taste nerve in the chorda tympani and a secondary taste cortex in the brain that are specifically activated by umami taste stimuli -'4--''. in this sense, it could be said that umami is a basic taste, independent of the four traditional basic tastes. The acceptability of foods is decided by many factors, such as taste, smell, color, temperature and overall appearance, as well as by physiological or mental conditions (Fig. 2). Among these factors, the most
SweetneSs~ Sourness Saltiness Bitternes
~
Umami m m m m Spicy taste , ~ =
1
Metallic taste ~ - Astringent taste == Amplitude tomb Continuity ~ , Aroma Texture ~ , Temperature Color ShaDe m Personal condition (mood & healtl~) Other factors ~ m r (environment, habituation, social situation,culture)
Fig. 2 Umami and other factors involved in food acceptability.
247
Table 1~-Taste-active ................................................................................... ocm sponet in seafoods(mg/100 gP'u Short-necked
Component
Abalone Seaurchin Snowcrab Scallop
clam
Glu Gly Ala Val
109 174 98 37
103 842 261 154
19 623 187 30
140 1925 256 8
90 180 74 4
Met Arg Tau
13 299 946
47 316 105
19 579 243
3 323
3 53 555
AMP IMP
90 ND ND 975 ND
10 2
32
2
-
-
K+
-
-
4 357 9 191 197
10 73 218
CI PO4)-
-
-
336
95
-
-
217
213
GMP Bet Suc Na•
7 1.2
5
784 172 ND ND
339
28 ND ND 42 65 244
273 322 74
aTaste.activecomponentsare indicatedin boldtype bAdaptedfromRef.30 ND, Not detected;-, not analysed Bet,Glycinebetaine;Suc,succinicacid;Tau,taurine
important direct factors are the basic tastes of sweet, sour, salty, bitter and umami. During the past two decades, a number of studies have investigated the umami taste from various perspectives: food science, biochemistry, psychophysics, neurophysiology, physiology, nutrition, etc. The results of many of these interdisciplinary studies were presented at two international symposia on umami: one was held in Kauai, Hawaii in 1985 and the other in Sicily, Italy in 1990. The proceedings of both of these symposia have been published (see Retg 27 and 28, respectively). Role of umami components in the taste of foods
Seafoods Foods are usually extracted by ethanol or hot water in order to analyse their taste components, in the case of seafoods, more than 90% of extracted nitrogen compounds can be accounted for by free and combined amino acids, nucleotides and related substances, organic bases, trimethylamine and trimethylamine oxides, ereatine and creatinine, and betaines. Non-nitrogenous compounds such as sugars and organic acids are also listed
as taste components -''),~". A synthetic extract can be prepared by mixing the various chemical components according to their known ratios in the food and adjusting the pH to that of the natural extract. The synthetic extract thus prepared usually reproduces well the taste of the natural extracP )..~:. To investigate the role of each component in a food, an omission test is often used. In an omission test, synthetic extracts with and without one or a group of components are prepared. The differences between pairs of extracts are then evaluated by the triangle difference test or paired difference test. Taste panelists are asked to determine differences between the two synthetic extracts and to evaluate the differences using five-point rating scales for specific taste components (i.e. sweet248
ness, sourness, saltiness, bitterness and umami) and flavor characteristics (e.g. complexity, thickness, overall preference). The results are analysed statistically and the taste-active components are disclosed. When the significance of each taste component was assessed in seafoods, umami compounds were found to be crucial in determining the distinctive taste of each type of seafood-". Table 1 shows the results of omission taste tests using synthetic extracts of seafoods 3". Both Glu and Gly were taste active in all five kinds of seafoods studied, irrespective of their levels. Furthermore, Glu in synthetic extracts not only elicited umami taste but also improved overall preference as a result of imparting continuity, thickness, complexity and mildness. An elevation of sweetness by Glu was recognized in all the synthetic extracts except for sea urchin, in which the extract without Glu was sweeter than that with Giu -~. Giy imparted sweetness in all the synthetic extracts. Ala was taste active only in sea urchin, snow crab and scallop 3", in which its level was relatively high. Arg was taste active in snow crab, scallop and short-necked clam. Although Arg is a bitter amino acid, it contributed to enhancing overall preferences such as continuity, thickness, complexity and mildness. Sodium and chloride ions are also important in producing the tastes of snow crab, scallop and short-necked clam. The common feature of synthetic extracts lacking Na ÷ was a remarkable decrease in sweetness, umami and characteristic overall flavor, and an increase in bitterness. Omission of CI- caused a dramatic change in the extract, creating an almost tasteless solution. The potassium ion was also taste active in the same three seafoods. Omission of K ÷ made the synthetic solutions watery, but the solutions retained a little umami and characteristic overall flavor. The phosphate ion was taste active only in snow crab. Its omission from the synthetic extract decreased saltiness, sweetness and umami. Thus, the taste-active components of the seafoods listed in Table 1 resembled each other even though the overall tastes of each of the seafoods were different. This suggests that not only the combinations of tasteactive components but also their relative amounts are important to produce the characteristic flavor of each seafood. Although the Glu content in snow crab extract is rather low compared with levels in the other seafoods, Glu makes a remarkable contribution to the distinct flavor characteristics of snow crab. Meats The extractive components of aged beef, pork and chicken have been analysed and the tastes of synthetic extracts consisting of free amino acids, IMP and NaCI have been evaluated -'7. Synthetic extracts containing free amino acids, including Glu, in addition to IMP and NaCI reproduced well the intensity of brothy, umami and salty tastes of natural soups. Thus, free amino acids and IMP contributed to the brothy and umami tastes of the meats. Trends in Food Science& TechnologyAugust 1993 lVol. 41
Evaluationscore Added MSG (0.2%, w/w)
Aroma/flavor characteristic
Tomatoes The contents of free amino acids, sugars and organic acids, which are dependent mostly on the ripeness and species, are related to the taste of tomatoes 34.35. Synthetic extracts have been prepared containing citric acid (4g), glucose (35g), KH2PO 4 (0.31 g), MgSO4-7H_,O (0.25g) and CaCi2"2H20 (0.22g) in l litre of watera*. Glu and Asp were added to the extracts in various proportions. Sensory tests showed that when the weight ratio of Glu (2.8 g) to Asp (0.7 g) was 4 in the synthetic extract, the taste was very similar to that of tomato. The appropriate ratio of Glu to Asp and the coexistence of both components were the most important factors in reproducing tomato flavor (Table 2). Citric acid was preferable to other organic acids such as lactic, malic and tartaric acids. AMP is the dominant nucleotide in tomato -~4,but the role of AMP as well as the synergistic effect between Glu and AMP are yet to be investigated.
Potatoes Free amino acids and 5'-nucleotides are known to contribute to the taste of potato. Raw potatoes contain only very small amounts of 5'-nucleotides, but the enzymatic hydrolysis of ribonucleic acids (RNA) in the potatoes during heat processing produces 5'-nucleotides in boiled potatoes. Boiled potatoes contain AMP (3mg/100g raw potato) and GMP (2.11 mg/100g raw potato). Taste tests using a synthetic mixture have shown that Glu (73.8mg/100g raw potato), Asp (46.8mg/100g raw potato) and 5'-nucleotides are consistently important in conveying an agreeable potato taste, though different potato species have different taste characters ~7.
Aroma
-1 '
Overall aroma Meaty
0 | :
~
Double-concentrated beef broth 0 +1 +2
+1 ' ;
I
'
!
I
Vegetable-like Acceptability
'
: -" "
_ ~L L " [
Basic taste
Overall taste
/
Satty
~
Sweet Sour Bitter
~ ~l .
" : :
:
.
~
-
:
- ]
Flavor characteristic
Continuity Mouthfulness Impact
|
. : : I : : • : : •
I I
Mildness
~
Thickness
I
.
. :
:
1
:
./1.~
Other flavor Spicy
Oily Meaty Vegetable-like
. I,i ~
Overall preference
l
--.-,=i,.4
Palatability I -1
0
+1
0
I
I
+1
+2
Fig. 3 Effectsof adding MSGand doubling the concentraliion of beef broth on the flavor profileof beefconsomme. A score of 0 indicates no effect; a positive score indicates an enhancement and a negative score a reduction in a given aroma/flavor characteristic. Adapted from Ref. 12.
Umami in broth
0
280
0
Similar in sweetness and sourness
280
0
-
Increase in umami; not similar
280
5.6
50
Taste flat; not similar
14
20
Good similarity
280
70
4
Best similarity; taste balance good
280
280
1
Good similarity
The function of umarni in dishes has been confirmed by sensor), evaluation ~:. Figure 3 shows the effects of added MSG on the flavor profile of beef consomm6. Added MSG had no effect on aroma but increased the overall taste intensity, while sweetness, sourness, saltiness and bitterness did not significantly increase. The addition of MSG also increased flavor characteristics such as continuity, 'mouthfulness', impact, mildness and thickness. Meaty flavor and the overall preference also increased. Doubling the concentration of beef broth in consomm6 gave a similar overall pattern of change in the flavor profile as the addition of MSG, and in addition increased the intensity of aromas and the four basic tastes.
280
560
0.5
Similar, but sourness strong
Sodium intake reduction
280
1120
0.25
Not similar and very i strong sourness t
Glu Asp (mg/lO0 ml) (mg/lO0 ml)
280
Similarity to natural extract
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
'~AdaptedfromRef.36 ...................................................................
Trends in Food Science & Technology August 1993 [Vol. 4]
:
:
/
Table L Effect on taste of the Glu: Asp ratio in synthetic tomato extracts a Weight ratio (Glu : Asp)
_.
: .
The umami taste itself is not palatable in its water solution, but it does convey palatability and improve taste when applied to food systems. Sensory tests in humans have shown that as the NaC! level in a food is ! reduced, acceptability of the food decreases. However, J
249
when a small amount of MSG is added, NaC! intake can be reduced without changing the acceptability of the food, in Japanese clear soup, levels of O.81% NaC! and 0,38% MSG gave optimal palatability ~s. The optimal NaCI concentration without using MSG was 0.92%. Thus, salt intake was reduced by 12% by using MSG in Japanese clear soup. MSG has also been reported to improve the palatability of an NaCl-restricted diet served in a hospital in Korea 3".
ology and the regulatory mechanism of umami preference are being presented in the l lth International Symposium on Oifaction and Taste (ISOT XI) held in Sapporo, Japan in July 1993. Another symposium, on 'umami taste and food intake', is being held at the 1 lth International Conference on the Physiology of Food and Fluid Intake (ICPFF! 11) in Oxford, UK in July 1993, covering the effects of umami on human appetite and the mechanism of umami preference.
Preference for umami
Acknowledgement
Nutritional
studies have s h o w n that the p r e f e r e n c e o f
rats for the umami taste is altered by changes in protein nutritional status, either a change in total protein intake or an alteration of the amino acid balance in the diet. Rats in a state of protein deficiency preferred NaC! and Gly solutions over umami (MSG or a mixture of MSG and GMP) solutions. A preference for NaC! may maintain electrolyte and body fluid balances. When the diet contained sufficient protein, rats preferred the umami solutions. Another study showed that rats have the ability to select a diet with a balanced amino acid content. When a Lys-deficient diet was offered, rats were able to distinguish a Lys solution from 15 other amino acids in solution. Once the amino acid balance in the diet was improved by the intake of a Lys solution, a preference for the umami solutions appeared ~". This means that a preference for the umami taste was induced when the level of dietary protein was within the normal range, but that a preference for NaCI was induced in a state of marginal protein deficiency. The regulatory mechanisms for this change of preference are currently being studied by behavioral and neurophysiological approaches. A recent study suggests that umami taste perception plays an important role in protein metabolism and in maintaining amino acid homeostasis within normal limits4~.
Conclusions Umami is the characteristic taste of glutamate and 5'-nucleotides. Psychophysical and electrophysiological studies indicate that umami is a taste sensation independent of the four basic tastes of sweet, sour, salty and bitter. Nutritional studies in rats suggest that a preference for the umami taste may be a taste marker for adequate protein intake.
Umami plays a major role in improving the palatability and acceptability of many foods. This could explain why tbods containing high levels of umami substances, such as tomato, cheese, fish sauces, etc., are often used for their flavorful qualities. When low levels of umami substances are added to a food, NaCI levels can be reduced without changing the palatability. 'Healthy eating' is a hot issue in many countries, and many people have a great interest in reducing their daily sodium intake. The salt-reduction effect of umami substances could be used to make a low-sodium diet more palatable. The most advanced researches on umami in the fields of food science, psychophysics, neurophysiology, physi250
We thank Mrs K. Ninomiya, of The Umami Manufacturers" Association of Japan, for kind assistance.
References 1 2 3 4 5 6 7 II
Ikeda, K. c! 9091 J. Tok~,'oChem. 5oc. 30, 820-8 36 Kodama,S. (19 ! 3 ~I. Tokyo Chem. 5oc. 24, 751-75 3 Kuninaka, A. ~1911(]!I. Agric. Chen~. Soc. lapan .34,487-4q2 Ueda, Y., Saka~,uchi, M., Hirayama, K.. Miyajima, R. and Kimizuka, A. ( l qqO) Agric. Biol. Chem. 54, 1613-16() Birch, G.G. and Keml), S.E. l lqBC)) Chem. Senses 14, 249-258 Kato, H. t1987)in UmamilKawamura, Y. and Kimura, S., eds), pp. 175-201, Eidai Sehsho, Tokyo, Japan Maeda, S., Eguchi, S. and Sasaki, H. (1958) I. Home Econ. Ilapam 9, 163-167 Giacometti, T. ~107c)~in Glutamic Acid: Advances in Biochemistry and Physiology IFiler,L.I.,Jr, Garatlini,S., Kare,M.R.,Reynolds,W.A.and
Wurtman,R.I.,edsJ. t)P. 25-]4. RavenPress Skurray,G.R.and Pucar, N. (1988)Food Chem. 27. 177-180 10 Rassin,E.R.,Sturma,I.A.and Gaull,G.E. tlC]78)Earh' HumanDe~. 2. 1-1 II Ma~a, I.A.I198It CRC (Trit. Rel . Food Sc i. Ntttr. 18~13L 2 ] I-312 12 Komata,Y. (Iq86~C)i~hi,~ato Ali~,l~a./tic)K,~gaktt, NikkanKogyo Shinhun,lapan 9
13 Ul4awa, T. and Kurihara, K. Am. I. Physiol. fin IIress~ 14 Yamagu(hi. ft. and Kimizuka, A. ~It)TCl~in C;h&tmi( Acid: Ad~ ante.~ in
15 15
l~iochemL~tr~and lqwsic)lo,t~r IFiler, L.I.. It, Garatlini. S.. Kate. M.R., Revmd(Is, W.A. antl Wurlman. R.I,, eds). lip. 35-54. Raven Pre~s Ikecla, S. l lqbSl Neu Food Ind. 7t12L 41-46 Fake, S. and Watanabe,K. (It)~]21in Um,imi Forum IqO2
IKawamura,Y,, ed.I, p. 5, Socielvfor Researchon UmamiTaste, Tokyo, lal)an Furukawa,H. (1qc]I I Nippon Nogeik,lgaku kaishi 65, 1(13-16q Yokotsuka,T., Sailo,N., Okuhara,A, and Tanaka,K. ~1q691Nippon No,v,eikagaku Kaishi 413,165-17(] I-lenning,H. II91O)Z. Pslz'hol. 74, 20J-21t) Yanlaguchi,S. I1()871ill Umami: A Basic Taste IKawamura,Y. and Kare,M.R.,edsL Pl).41-713,MarcelDekker Ninomiya,Y.and Funakoshi,M. (1987)illUmami: A BasicTaste (Kawamura,Y. and Kare,M.R.,etls),pp. 365-1385,MarcelDekker 22 Ohno, T., Yoshii,K. and Kurihara,K. 119841Bn~in Res. 1310,13-22 23 Kumazawa,T., Nomura,T. and Kurihara.K.~1t1881Bk~c'hemistn'27, 123t) 24 Yoshie,S., Wakasugi,C., Teraki,Y., Kanazawa,H., Iwanaga,T. and Fujita, T. I I qgl) Physiol. Behav. 4t), 887-880 Hellekanl, G. and Ninomiya, Y. (Iqqll PhysioL Beha~,.4q, g27-q34 26 Bavlis, L.L, and Roils, E.T. Ilqqll Physiol. Beha~. 4~1,~)73-~)7q 27 Kawamura, Y. and Kare, M.R., edsll c)871 Umami: A Basic Tasle, Marcel Dekker 28 Kawamura, Y., Kurihara, K., Nicolaidis, S., Oomura, Y. and Wayner, M.I, (lt)91) Plwsiol. Behav. 49(5)ISpecial Issue: Umami, Proceedings of the Second International Symposium on Umamil, PergamonPress 29 Watanabe, K,, Lan, H.L.,Yamaguchi,K.and Konosu,S. (19901Nihon Shokuhin Kogvo Gakkaishi 37, 439-445
Trends in Food Science & Technology August 1993 IVol. 41
30 31 32 33 34 35 36
Fuke,S. and Konosu, S. (1991) Physiol. Behav. 49, 863-868 Komala,Y. (1964) Nippon Suisan Gakkaishi 30, 749-756 Hayashi,T., Yamaguchi,K. and Konosu,S. (1981) I. Food Sci. 46, 479-483,493 Watanabe,K. and Konosu,S. (1987)in Umami(Kawamura, Y. and Kimura, S., eds), pp. 140-171, Eidai Sensho,Tokyo, lapan Inaba,A., Yamamoto,T., Ito, T. and Nakamura,R. ~1980)I, Ipn. Soc. Holt. Sci. 49, 425-441 Kader,A.A., Stevens,M.A., Albright, M. and Morris, I_.L.(1978) I. Am. Soc. Hort. Sci. 103,541-544 Okumura,S., Eguchi, S., Ogawa, W. and Suzuki, K. (1968)lapanese Patent Publication (Kokoku) No. 43-11731
37 Solms,I. and Wyler,R.(1979)in FoodTasteChemistrytAmerican ChemicalSocielySymposiumSeries115;,pp. 175-184,American ChemicalSociety 38 Yamaguchi,S. and Takahashi,C. (1984)Agric.Biol.Chem.48, 1077-1081 39 Kimura,S., Kim,C.H.,Otomo,M.I.,Yokomukai,Y., Komai,M.and Morimatsu,F. (1990)in Abstractof the SecondInternational Symposiumon Umami(Kawamura,Y.,ed.), pp. 52-53, Societyfor 40
41
Researchon Umami Taste,Tokyo, Japan Torii, K., Mimura, T. and Yugari,Y. i1987) in Umami: A Basic Taste (Kawamura,Y. and Kare,M.R., eds), pp. 513-563, Marcel Dekker Tabuchi,E., Ono, T., Hishijo, H. and Torii, K. (1991) Physiol. Behav. 49, 951-964
Review
:i Fungal starter cultures Mould-fermented foods are produced with the help of fungal starter cultures, which are added to the foods as spore suspensions to ensure predictable fermentation results. Most
!!
fungal strains used today are screened and isolated from the native pool of organisms found in the food habitat. These strains do not always meet the requirements of modern food production. Few strains are toxicologically unobjectionable,
for fermented foods: molecular aspects
!i
and methods for developing new strains with new characteristics would be advantageous. This article discusses the cur-
ii Rolf Geisen
rent status of gene technology methods to improve fungal starter cultures for the production of mould4ermented foods.
An isolated strain for use as a starter culture should fulfil several requirements: • it should not be toxinogenic:
Mould-fermented foods play an important role in the human diet, especially in Asian countries. Shoyu, miso, katsuobushi, tempeh, sufu, oncom and ankak are just some of the Asian fermented foods produced by strains from the genera Aspergillus, Rhizopus, Actinomucor, Neurospora and Monascus'. Within the European market a limited number of mould-fermented foods are produced. Only a few fungal species are used for the production of these foods, all belonging to the genus Penicillium: P. camemberti for the production of white cheeses (Brie and Camembert), P. roqueforti for the production of blue cheeses (Roquefort, Gorgonzola, Stilton and Gammelost), and P. nalgiovense and P. cluysogenum for the production of meat products (salami-type sausages). Fungal starter cultures contribute to a large extent to the flavour and texture of the fermented food due to the action of various exoenzymes ~. Excreted proteases produce flavour-active peptides and amino acidsL Lipases produce free fatty acids, which can be converted to methyl ketones, alcohols or aldehydes, important for flavour formation 4. Rolf Geisen is at the Federal Research Centre for Nutrition, Institute of
Hygiene and Toxicology, Engesserstr.20, 76131 Karlsruhe,Germany. Trends in Food Science & Technology August 1993 IVol. 41
• it should not produce an antibiotic: • it should be adapted to the food product: • it should produce the appropriate amounts of proteases and lipases: • it should be antagonistic against pathogenic or spoilage bacteria characteristic of the fermented product: • iit should not produce any off-flavours. By far, most naturally isolated strains do not cover all of these requirements. However, using gene technology methods it should be possible to improve the characteristics of these strains.
Benefits of gene technological modification of fungal starter cultures Due to the ability of most Penicillium spp. to produce mycotoxins -~, only a limited number of strains arc available that are nontoxinogenic and can be regarded as GRAS ('generally recognized as safe'). Fungal starter cultures should not produce any mycotoxin or antibiotic. However, these requirements are not fulfilled even by currently used strains. All strains of P. camemberti ©1,),~L FlsvvierS(it.me Publishers Lid.dJKt (~q24-2244")I.'$(1(,.(111
251