Amino acid derivatives of creatinine as seasoning material

Abstract: The invention provides novel amino acid derivatives represented by formula (1) as well as their structural isomers and their hydrolysates In this formula X and Y are each N or NH, Z is O or OH, (1) when X=N and Y=NH, Z=0, and *1 and *3 are double bonds, (2) when X=NH and Y=N, Z=0, and *2 and *3 are double bonds, (3) when X=N and Y=N, Z=OH, and *2 and *4 are double bonds, and R is a side chain derived from a naturally occuring amino acid. These amino acid derivatives are useful as a component of a seasoning material which gives foods a "thick sour taste" in the neutral pH region.

Description: Field of the Invention The present invention relates to amino acid derivatives that give foods a "thick sour taste" in a neutral pH region. Prior Art Natural extracts such as meat extract, chicken extract, extract of fishes and shells and vegetable extract have been widely used commercially as basic seasonings of foods. It is considered that these natural extracts serve to give foods a complicated, deep, substantial taste, making up for an insufficient taste of food materials. Problems to be Solved by the Invention However, since these natural extracts are costly and hard to obtain, processed products and substitutes using part of these natural extracts have been produced and marketed. Basic stocks of a dried bonito, dried small sardines, sea weed and Cortinellus shiitake and flavor seasonings obtained by adding salt, sugar, flavor, amino acid and the like to these natural materials have been also widely used. These commercial processed products and substitutes of the natural extracts are made up of low-molecular substances such as amino acids (mainly sodium glutamate), nucleic acids and organic acids. Accordingly compared with the natural extracts, these are defective in that the taste is plain and flat. In order to improve this defect, the substantial, complicated taste has been given so far by adding hydrolyzed vegetable protein (HVP), hydrolyzed animal protein (HAP), yeast extract and the like. However, HVP and HAP have an odor caused by hydrolysis, and the yeast extract has an odor peculiar to the yeast. Accordingly, the amounts of these materials used are naturally limited, and clearly different in taste and flavor from the natural extracts as a model. Therefore, these materials are not satisfactory, especially with respect to the "thick sour taste" and the "sharp, deep taste" by which the whole taste of foods is improved. Means for Solving the Problems The present inventors have conducted investigations to increase the seasoning power of the natural extract substitutes and basic stocks and to give the "thick sour taste". As a result, they have collected fractions that give the "thick sour taste" from a beef extract obtained by the treatment with hot water through a dialysis membrane, electrodialysis membrane, gel filtration chromatography, partition chromatography and reverse-phase chromatography, and have finally succeeded in isolating novel amino acid derivatives having the below mentioned properties. Further, they have also succeeded in obtaining the novel amino acid derivative by using commercial reagents as starting materials through a chemical synthesis method. Summary of the Invention This invention relates to a group of new compounds having excellent characteristics when used as a seasoning material, i. e. a novel amino acid derivative represented by formula (1) and/or an analogue thereof wherein X and Y are each N or NH, Z is O or OH, (1) when X is N and Y is NH, Z is O and *1 and *3 are double bonds, (2) when X is NH and Y is N, Z is O and *2 and *3 are double bonds, (3) when X is N and Y is N, Z is OH and *2 and *4 are double bonds, and R is a side chain of a naturally occuring amino acid, wherein the analogue is represented by formula (2) which is a structural isomer of the compound of formula (1) wherein X and Y are each N or NH, Z is O or OH, (1) when X is NH and Y is N, Z is O and *1 and *4 are double bonds, (2) when X is N and Y is NH, Z is O and *2 and *4 are double bonds, (3) when X is N and Y is N, Z is OH and *1 and *3 are double bonds, and R is a side chain of a naturally occuring amino acid, formula (3) which is a hydrolyzate of the compound of formula (1) wherein X and Y are each NH 2 or NH, (1) when X is NH 2 and Y is N, *2 is a double bond, (2) when X is NH and Y is NH, *1 is a double bond, and R is a side chain of a naturally occuring amino acid; or formula (4) which is a hydrolyzate of the compound of formula (1) wherein X and Y are each NH 2 or NH, (1) when X is NH 2 and Y is N, *2, is a double bond, (2) when X is NH and Y is NH, *1 is a double bond, and R is a divalent residue of a naturally occuring amino acid. The invention further relates to a seasoning material comprising one or more of the compounds of formulae (1) to (4) as a component. In the formulae of these compounds the residue R preferably represents in formulae (1) to (3): H (glycine), -CH 3 (alanine), -CH 2 CH 2 COOH (glutamic acid) or-CH 2 CH 2 CH 2 CH 2 NH 2 (lysine); and in formula (4): -COCH 2 - (asparagine), -COCH 2 CH 2 -(glutamine), -C(NH)NHCH 2 CH 2 CH 2 - (arginine) or -CH 2 CH 2 CH 2 CH 2 -(lysine). In the following, examples of the novel amino acid derivatives useful as components of a seasoning material are represented by formulae (5) to (12). One example of the amino acid derivatives having the basic structure of formula (1) and isolated from beef extract has the following characteristics: Molecular weight: 185 Molecular formula: C 7 H 11 N 3 O 3 Structural formula: 1) N-C1-methyl-4-oxo-2-imidazolin-2-yl)alanine Structural formula: 2) N-(1-methyl-4-oxo-imidazolidin-2,2-iridene) alanine Structural formula: 3) N-(1-methyl-4-hydroxy-3-imidazolin-2,2-iridene)guanine Further, the isolated fraction of the novel amino acid derivative was concentrated, and an alcohol was then added thereto. The mixture was allowed to stand at room temperature. It was observed that colorless transparent laminar crystals were formed. As a result of X-ray crystal structure analysis thereof, it was found that the compound of the present invention was converted into the structural isomer [structural formulas (4), (5) and (6)] by crystallization. Structural formula: 4) N-(5-methyl-4-oxo-1-imidazolin-2-yl)sarcosine Structural formula: 5) N-(4-methyl-5-oxo-1-imidazolin-2-yl)sarcosine Structural formula: 6) N-(4-methyl-5-hydroxy-2,5-imidazol-2-yl)sarcosine It was confirmed that in solution, part of the compound was ring-opened by hydrolysis to form a substance of structural formula (11) or (12). Structural formula: 7) N-[1-(N-carboxymethyl-N-methyl)amino-1-iminomethyl] alanine. Structural formula: 8) N,N-[1-(N-carboxymethyl-N-methyl)amino-1-aminomethylidene]alanine. The novel amino acid derivatives of the present invention, represented by formula (1) may be synthesised by reacting creatinine with an α-halogeno carboxylic acid and/or its ester according to the following general synthesis scheme to produce the corresponding carboxylic acid and/or ester compound and if necessary, cleaving off the ester group by general methods of hydrolysis such as treatment with an alkaline reagent. wherein R represents a residue derived from a naturally ocurring amino acid, R' is H or an alkyl, preferably methyl and Y' denotes a halogen atom, preferably Br or Cl. Some examples of reagents and the resulting amino acid residues are given in the following table: Residue Reagent alanine methyl 2-bromopropionate glycine ethyl bromoacetate lysine methyl ε-benzoylamino-α-chlorocaprate glutamic acid methyl α-chloroglutarate leucine methyl α-bromoisocaprate The reaction between creatinine and the α-halogeno carboxylic acid or its ester may be carried out in a suitable solvent, for example dimethyl formamide, and in a broad temperature range from room temperature up to the reflux temperature of the solvent. A preferred temperature range is from about 30 to 80 °C. In order to obtain the structural isomers represented by formula (2) the compounds of formula (1) are dissolved under heating in a suitable solvent, for example a mixture of a lower alcohol and water and the compound is crystallized. According to a preferred example of the crystallization process the compound of formula (1) is dissolved in a mixture of methanol and water under heating. The obtained solution is set aside for several hours, preferably overnight, at room temperature to precipitate crystals having the structure of formula (2). The formed crystals are isolated by filtration and washed with methanol. The compounds represented by formulae (3) and (4) can be produced by hydrolysis under alkaline conditions. For example, the compound of formula (2) is converted into the compound of formula (3) by leaving the compound to stand in 1N NaOH-solution overnight at room temperature. The present inventors have found that the compound of the present invention, unlike other known organic and inorganic acids, gives the sour taste even in the neutral pH region, and that if the compound of the present invention is added to the processed products and substitutes of the existing natural extracts or to the basic stocks, it is possible to increase the seasoning power thereof, to improve the whole taste and to give the "thick sour taste" and the "deep taste". These findings have led to the completion of the present invention. Further, the compound of the present invention can decrease a heavy aftertaste and change it into a light taste by being added to foods having an unpleasant aftertaste. That is, the present invention relates to a seasoning material containing a novel amino acid derivative represented by formula (1), (2), (3) or (4) [for example, structural formula (1), (2), (3), (4), (5), (6), (7) or (8)]. The novel amino acid derivative of the present invention is added to the above-mentioned processed products and substitutes of the natural extracts or to the basic stocks to give the existing seasonings the "thick sour taste". The present invention also provides a process for producing the processed products and substitutes of the natural extracts having the high-quality taste similar to those of the natural extracts, as well as a process for producing a high-quality basic stock. The "thick sour taste" here refers not to a sour taste that sharply stimulates a tongue, this sour taste being provided by organic acids (for example, citric acid, succinic acid, lactic acid and phosphoric acid) ordinarily used in food processing, but to a mild sour taste peculiar to the natural extracts that spreads throughout the mouth. The materials of the sour taste such as these organic acids and acidic amino acids, needless to say, do not exhibit the sour taste in the neutral pH region and cannot give the "thick sour taste". Moreover, anserine, carnosine, creatine, creatinine, nucleic acids and saccharides which are known to have a seasoning property do not exhibit the sour taste in the neutral pH region. The animals and vegetables which are used in the present invention are not particularly limited. Those ordinarily used in the food industry, such as beef, pork, chicken, fish and the like can be optionally used. The substance that gives the "thick sour taste" even in the neutral pH region can be also obtained by treating the yeast extract in like manner. The novel amino acid derivative that gives the "thick sour taste" in the present invention can be formed, for example, by removing remains, precipitates, fats and oils from beef water extract or hot water extract through a centrifugal separator or filter, then charging the extract into a commercial cellulose-type dialysis membrane, dialyzing the extract against water to remove high-molecular substances, and treating the dialyzate with an electrodialysis membrane or a column for gel filtration, partition chromatography, reverse-phase chromatography or the like. Of course, the novel amino acid derivative of the present invention can be obtained by a synthesis method using creatinine, alanine or the like as a starting material. It has been found that the thus-obtained novel amino acid derivative of the abovementioned structure which has the molecular weight of 185 and which gives the "thick sour taste" to a stock of a Japanese food, for example, a stock of a dried bonito, chicken, fishes, shells, beef or Cortinellus shiitake, a soup stock of a Western food, for example, a stock of beef, chicken, pork, fishes or shells, or a soup of a Chinese food, for example, a stock of beef, chicken, pork, ham, eyes of scallop, ear shell, shrimp, dried cuttlefish, Cortinellus shiitake, Chinese cabbage or celery to increase the taste. Further, when the novel amino acid derivative is added to the processed products and substitutes of the natural extracts, especially, HVP, HAP and yeast extract which can be used as the amino acid mixture at relatively low cost, or to inexpensive beef extract, it deepens the whole taste, gives the "thick sour taste" and increases the taste, providing the high-quality taste. The optimum concentration of the novel amino acid derivative that gives the "thick sour taste" varies depending on foods and seasonings to which it is added. In either case, the compound of the present invention is added such that the concentration of it in solution becomes from 0.01 to 0.5% by weight (in terms of a solids content), whereby it is possible to provide the "thick sour taste" which is lacking in the conventional stocks, to arrange the whole taste and to suppress the flat taste. Further, the compound of the present invention can effectively decrease the heavy aftertaste and change it into a light taste by being added to foods having an unpleasant aftertaste. The novel amino acid derivative that gives the "thick sour taste" in the present invention has a strong function of imparting the taste, and it can be used as a seasoning, added to processed foods, nutritious foods and medical foods and further effectively utilized as resources of marine products. This compound may be added as such or after having been dissolved in water. The process for producing the abovementioned amino acid derivative that gives the "thick sour taste", results of analysis of the structure thereof, and results of addition thereof in the present invention are illustrated by referring to the following Examples. However, the present invention is not at all limited to these Examples. Preparation Example 1 : Extraction Approximately 6 kg of a beef shank meat were cut to a square of from approximately 5 to 10 cm, charged into a 30-liter cylindrical aluminum pot, and boiled at from 90 to 95°C for approximately 7 hours with the addition of 8 liters of water to obtain approximately 5 liters of a hot water extract. The beef and precipitate formed were removed from the hot water extract, and the residual extract was then refrigerated overnight. The oils, fats and precipitate formed during the refrigeration were further removed through a 60-mesh sieve. Further, the fine precipitate and solids were removed by a Sharples type ultra-centrifuge (15,000 rpm, manufactured by Nakamura Denki Seisakusho). The brown transparent supernatant obtained by the centrifugation was freeze-dried. The freeze-dried powder was dissolved in water to a concentration of 8 g/dl, and a high-molecular substance was fully removed by means of an ultrafiltration membrane (fraction molecular weight=10,000). The thus-obtained low-molecular fraction solution was treated with an electrodialysis membrane (microdialyzer G3 manufactured by Asahi Chemical Industry Co., Ltd., membrane pore diameter molecular weight=approximately 1,000). The obtained outer solution (molecular weight=approximately 1,000 or less) was further treated with an electrodialysis membrane (membrane pore diameter molecular weight=approximately 100) to obtain an inner solution fraction which was a fraction of a beef hot water extract having a molecular weight of from approximately 100 to 1,000. The resulting solution was powdered by freeze-drying. In the treatment with the electrodialysis membrane, a point at which the conductivity and the current value of the dialyzate became zero was defined as a final point. The thus-obtained fraction of the beef hot water extract having the molecular weight of from approximately 100 to 1,000 was subjected to various methods such as gel filter chromatography (Sephadex G-25 column, 50 x 540 mm, manufactured by Pharmacia Biotek, eluent: 20mM-ammonium acetate),partition chromatography (HPLC, TSKgel Carbon 500 column, 21.5 x 150 mm, manufactured by Tosoh Corp., eluent: 0.05% TFA → 0.05% TFA/acetonitrile = 50/50 gradient), and reverse-phase chromatography (HPLC, Capcellpak C18 UG120 column, 20 x 250 mm, manufactured by Shiseido Co., Ltd., eluent: 0.05% TFA → 0.05% TFA/acetonitrile = 50/50, gradient) to collect a substance that gives the "thick sour taste". The purity of the collected substance was measured by reverse-phase chromatography (HPLC, Ultron VX-ODS column, 4.6 x 250 mm, manufactured by Shinwa Kako K.K., eluent: 0.05% TFA → 0.05% TFA/acetonitrile = 50/50 gradient). As a result, the substance was found to be almost a single substance. Analysis Example The physicochemical properties of the substance that gives the "thick sour taste" as obtained in the abovementioned Preparation Example are as follows. Results of analysis of the molecular weight: The novel amino acid derivative obtained from the beef hot water extract by the abovementioned method has the following properties. The molecular weight of the compound was found to be 185 as measured by fast atom bombardment analysis (hereinafter abbreviated as "FAB-MS"). Results of analysis of the molecular formula: The molecular formula of the compound was determined to be C 7 H 11 N 3 O 3 as measured by 1H-NMR and 13C-NMR. Results of analysis of the structural formula: From the results of measurement by 1H-NMR and 13C-NMR, it was presumed that the skeleton of alanine or lactic acid was present and the skeleton similar to that of creatinine was present. The novel amino acid derivative was deemed to be a condensed structure of the abovementioned two moieties as measured by heteronuclear mutual remote bonding correlation (HMBC) analysis, and the abovementioned structures (5), (6) and (7) were presumed. Incidentally, the compound of the present invention was found to be a set of structural isomers as measured by NMR spectrum. Results of analysis of X-ray crystal structure: Methyl alcohol was added to the concentrated solution of the compound of the present invention in an amount of approximately 4 times, and the mixture was allowed to stand at room temperature. A few days later, colorless transparent laminar crystals were precipitated, and then filtered under reduced pressure to collect crystals. The crystals were subjected to X-ray crystal structure analysis. As a result, the crystals were found to have the abovementioned structures (8), (9) and (10). That is, it was found that the structures (5), (6) and (7) were changed into the structures (8), (9) and (10) of the structural isomers by the crystallization. Evaluation of a function of imparting the "thick sour taste": The function of imparting the "thick sour taste" which was provided by the thus-obtained novel amino acid derivative was evaluated by adding the novel amino acid derivative to a commercial consomme soup such that the solids content became 0.05% by weight in terms of a solids content. Profile evaluation of the function was conducted by five panelists. As a result, it was found that the sample containing the novel amino acid derivative imparted the "thick sour taste" to the commercial consomme soup. Further, in order to measure the suitable amount of the novel amino acid derivative added, the novel amino acid derivative was added to the commercial consomme soup in an amount of 0.01% by weight, 0.03% by weight, 0.05% by weight, 0.1% by weight, 0.2% by weight or 0.5% by weight (in terms of a solids content). The suitable amount of the novel amino acid derivative added was evaluated by the panelists. As a result, it was found that the sample containing the novel amino acid derivative increased the substantial, thick taste without changing the flavor of the commercial consomme soup as a control, and that it deepened the whole taste and gave the "thick sour taste". However, with the addition of 0.2 % or more of the novel amino acid derivative, no big difference was found. From the economical standpoint, the amount of approximately 0.05% by weight was estimated to be sufficient. In this manner, the novel amino acid derivative was added to the commercial consomme soup, and the organoleptic evaluation was conducted. The mixing ratio was as follows. That is, hot water was added to one cube (5g) of the commercial consomme soup and 0.3 g of the novel amino acid derivative powder of the present invention such that the total amount was 300 ml. As a control, a consomme soup not containing the novel amino acid derivative was prepared. The two types of the soups were subjected to the organoleptic evaluation by 20 taste panelists through a 2-point comparison method. The results are shown in Table 1. Soup containing the novel amino acid derivative Control soup Preferable flavor 13 7 Preferable taste 12 8 "Thick sour taste" which is stronger. 18 2 Lighter aftertaste 18 2 More complicated taste 17 3 Preferable as a whole 17 3 Remarks Unpleasant aftertaste is decreased and the taste becomes light. Nothing particular. Preparation Example 2 : Chemical synthesis Seventy grams of reagent creatinine (made by Nacalai Tesque Co.) and 114 ml of reagent methyl-2-bromopropionate (made by Merck Japan) were used as starting materials, and approximately 15 grams of the abovementioned novel amino acid compound were obtained as schematically shown below. The structure of the obtained compound was analyzed by the abovementioned FAB-MS, 1H-NMR and 13C-NMR, and was then found to be the same as the structure of the compound obtained from the beef hot water extract. At this time, the yield of the compound was approximately 12 mol%. Example 3 : A 0.5-M solution of reagent creatinine (made by Nacalai Tesque Co.,) and a 0.5-M solution of alanine (made by Ajinomoto Co., Inc.) were heated at a pH of 10 for 30 hours. The obtained reaction solution was treated with a DEAE TOYOPEARL (11.2 cm x 20 cm) column to remove unreacted creatinine and alanine. At this time, the eluent was 20-mM ammonium acetate, the flow rate was 18.5 ml/min, and the detection was conducted with absorbance at 280 nm. The content of the novel amino acid derivative in each fraction was analyzed by a Carbon 500 column. Further, the fraction containing this novel amino acid derivative was collected and concentrated. Subsequently, the novel amino acid derivative was singly collected by means of a Carbon 500 column for collection. The structure of the obtained compound was analyzed by the abovementioned FAB-MS, 1H-NMR and 13C-NMR, and it was found to be the same as that of the compound obtained from the beef hot water extract. Evaluation of a function of imparting the "thick sour taste": It was confirmed that both of the novel amino acid derivatives prepared by the chemical synthesis and the heat-formation had the same function of imparting the "thick sour taste" as the novel amino acid derivative isolated from the beef hot water extract. Effects of the Invention The seasoning material containing the novel amino acid derivative of the present invention is added to processed products and substitutes of natural extracts or basic stocks, whereby the "thick sour taste" can be given to these existing seasonings to provide the processed products and substitutes of the natural extracts or the basic stocks that give the high-quality taste similar to the taste of the natural extracts. Brief Description of the Drawings Fig. 1 is a Ultron VX-ODS column chromatography chart of an isolated sample obtained in Preparation Example. Fig. 2 is an FAB-MS chart of the isolated sample obtained in Preparation Example. Fig. 3 is a 1H-NMR chart of the isolated sample obtained in Preparation Example (pH=approximately 2). Fig. 4 is a 13C-NMR chart of the isolated sample obtained in Preparation Example (pH=approximately 2).

Claims: A novel amino acid derivative represented by formula (1) and/or an analogue thereof wherein X and Y are each N or NH, Z is O or OH, (1) when X is N and Y is NH, Z is O and *1 and *3 are double bonds, (2) when X is NH and Y is N, Z is O and *2 and *3 are double bonds, (3) when X is N and Y is N, Z is OH and *2 and *4 are double bonds, and R is a side chain of a naturally occuring amino acid, wherein the analogue is represented by formula (2) which derivative is a structural isomer of the compound of formula (1) wherein X and Y are each N or NH, Z is O or OH (1) when X is NH and Y is N, Z is O and *1 and *4 are double bonds, (2) when X is N and Y is NH, Z is O and *2 and *4 are double bonds, (3) when X is N and Y is N, Z is OH and *1 and *3 are double bonds, and R is a side chain of a naturally occuring amino acid, formula (3) which derivative is a hydrolyzate of the compound of formula (1) wherein X and Y are each NH 2 or NH, (1) when X is NH 2 and Y is N, *2 is a double bond, (2) when X is NH and Y is NH, *1 is a double bond, and R is a side chain of a naturally occuring amino acid, or formula (4) which derivative is a hydrolyzate of the compound of formula (1) wherein X and Y are each NH 2 or NH, (1) when X is NH 2 and Y is N, *2 is a double bond, (2) when X is NH and Y is NH, *1 is a double bond, and R is a divalent residue of a naturally occuring amino acid. The amino acid derivative of claim 1, wherein the R represents H (glycine), CH 3 (alanine), CH 2 CH 2 COOH (glutamic acid), or CH 2 CH 2 CH 2 CH 2 NH 2 (lysine). The amino acid derivative of claim 1, wherein R represents -COCH 2 - (asparagine), -COCH 2 CH 2 - (glutamine), -C(NH)NHCH 2 CH 2 CH 2 -(arginine) or -CH 2 CH 2 CH 2 CH 2 -(lysine). A seasoning material comprising as a component an amino acid derivative of any of the claims 1 to 3.

Inventors: HARADA TSUTOMU, HONDA YUTAKA, SHIMA KEIGO, SUZUKI EIICHIRO, HARADA, TSUTOMU, HONDA, YUTAKA, SHIMA, KEIGO, SUZUKI, EIICHIRO, Harada, Tsutomu, c/o Food Research &amp; Development, Honda, Yutaka c/o Central Research Laboratories, Shima, Keigo, c/o Food Research &amp; Development, Suzuki, Eiichiro c/o Central Research Laboratories
Applicants: AJINOMOTO KK, AJINOMOTO CO., LTD.
Application year: 1995
Main classification: C07D233
IPC codes: A23L1, C07C229, C07C279, C07D233