Process for the preparation of a savory flavor

A process for preparing a savory flavor, the process comprising reacting a compound of general formula X with hydrogen sulphide and/or cystein, wherein ##STR1## in which R.sup.1 represents an alkyl group having 1 or 2 carbon atoms or hydrogen, R.sup.2 represents an alkyl group having from 1 to 4 carbon atoms or hydrogen, R.sup.3 represents an alkyl group having from 1 to 5 carbon atoms or hydrogen and R.sup.4 represents hydrogen or an organic radical consisting of from 1 to 6 carbon atoms, hydrogen and from 0 to 2 oxygen atoms. X is preferably 4-hydroxy-2,5-dimethyl-2-(2-hydroxy-3-oxo-2-butyl)-3(2H)-furanone, and is formed from the reaction of 4-hydroxy-2,5-dimethyl-3(2H)-furanone and diacetyl. 2,5-dimethyl-4-mercapto-3(2H)-furanone is a flavor compound obtainable by this process.

FIELD OF THE INVENTION 
The present invention relates to savoury flavours, processes for their 
preparation, and their use in the flavouring of foodstuffs. In particular, 
this invention is concerned with savoury flavours which resemble that of 
roast, fried or boiled meat. 
Flavouring is understood to be the incorporation of compounds having 
flavouring characteristics per se, as well as the incorporation of 
precursor compounds which may not themselves possess flavouring 
characteristics, but which during the preparation of foodstuffs release or 
are converted into products having flavouring characteristics. 
BACKGROUND ART 
Processes for the preparation of savoury flavours are known in the art: 
GB 1256462 discloses meat-like flavouring compositions and methods of 
preparing them. The flavouring compositions comprise organic 
oxygen-containing heterocyclics wherein the second carbon atom from the 
oxygen atom contains a sulphur substituent. 
GB 1434194 describes the preparation of addition compounds from the 
reaction of mono- or dialkylfurenidones (e.g. 
2,5-dimethyl-4-hydroxy-3-(2H)-furanone) with carbonyl compounds, such as 
ketones. These addition compounds are stable upon storage and, since they 
are precursors of furenidones, they can be incorporated into foodstuffs 
where, upon heating of the foodstuffs, they revert to free furenidones, 
which have flavouring properties. 
GB 1283912 and GB 1283913 describe processes for preparing meat-like 
flavouring substances; the processes comprise reacting certain 
heterocyclic ketones, such as 
4-hydroxy-2,5-dimethyl-2,3-dihydrofuran-3-one or 
4-hydroxy-5-methyl-2,3-dihydrofuran-3-one, with hydrogen sulphide or other 
sulphur-containing compounds (e.g. cysteine) in the presence of water. 
Although, these processes permit the synthesis of interesting savoury 
mixtures, they are not very specific, so do not form high yields of key 
meat flavours (eg. see Examples B1 and B2 of GB 1283912). 
EP-A-571031 discloses a process for the preparation of a savoury flavour 
which comprises reacting mono- and/or di-methyl-3(2H)-furanone, or 
precursors thereof, with cystein and/or hydrogen sulphide. No hydroxy 
group is carried in the four position. A suitable precursor is 
2,5-dimethyl-2-(2-hydroxy-3-oxo-2-butyl)-3(2H)-furanone, which is a 
diacetyl oligomer. The process results in high yields of certain key 
compounds, namely methyl-substituted furanthiols, their disulphides and 
methyl-substituted furanthiolacetates. The reaction of 
2,5-dimethyl-2-(2-hydroxy-3-oxo-2-butyl)-3(2H)-furanone with H.sub.2 S and 
cystein results in a 32% yield of 2,5-dimethyl-furan-3-thiol (see example 
8 of EP 571031 and comparative example D of the present application): FIG. 
2 of the present application is a chromatograph of the resultant savoury 
flavour mixture showing that this key sulphur-containing flavour compound 
(peak 8) is present. 
The present invention seeks to provide a new process for preparing a 
savoury flavour mixture, the process preferably providing a good yield of 
a number of key flavour compounds. 
SUMMARY OF THE INVENTION 
According to the present invention there is provided a process for the 
preparation of a savoury flavour, the process comprising reacting a 
compound of general formula X with hydrogen sulphide and/or cystein, 
wherein 
X is: 
##STR2## 
in which R.sup.1 represents an alkyl group having 1 or 2 carbon atoms or 
hydrogen, R.sup.2 represents an alkyl group having from 1 to 4 carbon 
atoms or hydrogen, R.sup.3 represents an alkyl group having from 1 to 5 
carbon atoms or hydrogen and R.sup.4 represents hydrogen or an organic 
radical consisting of from 1 to 6 carbon atoms, hydrogen and from 0 to 2 
oxygen atoms. 
Compound X occurs in two stereo-isometric forms; both forms are suitable as 
flavour precursors for the purpose of this invention. 
Preferably, compound X is formed by reacting a compound of general formula 
Y with a compound of general formula Z where Y is: 
##STR3## 
and Z is: 
##STR4## 
Preferred examples of compound Y are 4-hydroxy-2,5-dimethyl-3(2H)-furanone, 
4-hydroxy-2-methyl-3(2H)-furanone, 4-hydroxy-5-methyl-3(2H)-furanone, 
3-hydroxy-2,5-dimethyl-4(5H)-furanone, 3-hydroxy-2-methyl-4(5H)-furanone, 
and 3-hydroxy-5-methyl-4(5H)-furanone. 
Preferred examples of compound Z are diacetyl, butanal, hexanal, pyruvic 
aldehyde, pyruvic acid, acetoin, acetol, ethylene glycol aldehyde, 
pentanedione and glyceraldehyde. 
In a particularly preferred embodiment, Y is 
4-hydroxy-2,5-dimethyl-3(2H)-furanone, i.e. 
##STR5## 
Z is diacetyl, i.e. 
##STR6## 
and the adduct formed from the reaction of Y and Z is 
4-hydroxy-2,5-dimethyl-2-(2-hydroxy-3-oxo-2-butyl)-3(2H)-furanone, which 
is X. 
Preferably, compound X is reacted with both cystein and hydrogen sulphide. 
Hydrogen sulphide may be generated by a hydrogen sulphide donor. Suitable 
hydrogen sulphide donors can be any organic or inorganic compound which is 
capable of generating hydrogen sulphide either in the gaseous or nascent 
form under reaction conditions. Suitable examples are: peptides containing 
cystein such as glutathione, cystine, mercaptoaceetamide, thioaceetamide, 
or salts thereof, for example: potassium or sodium salts, hydrochlorides, 
esters or simple derivatives of other simple derivatives of the 
sulphur-containing compound. Suitable inorganic sulphur-containing 
compounds are sulphides or hydrosulphides of alkali metals, alkaline earth 
metals or ammonia, such as sodium sulphide, potassium sulphide, ammonium 
sulphide, calcium sulphide, and the corresponding hydrosulphides. Also 
other metal sulphides, for example ferrous sulphide may be used. The use 
of hydrogen sulphide donors obtained from animal, vegetable or 
microbiological sources is preferred. 
In another preferred embodiment of the invention the molar ratio of 
compound X: cystein: hydrogen sulphide available for reaction is within 
the range 1:5-15:0-10, preferably within the range 1:7-9:3-5. 
A flavour compound obtainable by this process is 
2,5-dimethyl-4-mercapto-3(2H)-furanone. 
In order to obtain higher yields of flavour compounds the process according 
to the present invention is preferably carried out in a medium comprising 
a polar solvent, preferably an organic polar solvent. In an aqueous 
medium, it is usual to obtain lower yields than in a polar organic medium. 
As the presence of water may negatively affect the yield, the present 
reaction medium contains preferably less than 20%, more preferably less 
than 5%, of water. Many organic polar solvents are suitable in principle, 
but preferred are those whose presence is allowed in foods by the various 
food regulations, such as propylene glycol or glycerol. Commercial grades 
thereof often contain about 1% of water and can be used as such. 
Preferably the process is carried out at a pH below 7, preferably from 2 to 
6. The pH of the reaction mixture is conveniently determined after adding 
90% (w.w.) of water to 10% of the organic polar medium. Usually the pH of 
the reaction medium increases somewhat as the reaction proceeds. 
The process according to the present invention is preferably carried out at 
a temperature between 60 and 180.degree. C. for 0.5 to 4 hours, preferably 
between 90 and 120.degree. C. for 1 to 3 hours. The use of higher reaction 
temperatures tends to lead to savoury flavours with a roast meat note, 
whereas those prepared at lower temperatures tend to lead to a more sweet 
meaty note. Lower temperatures (eg 100.degree. C.) are preferred. 
The process according to the present invention is preferably carried out in 
an autoclave at superatmospheric pressure, preferably from 100 to 2,500 
KPa, optionally in the presence of air. The use of an autoclave is 
convenient, especially when using hydrogen sulphide, and it may be 
desirable to effect some air oxidation so as to form the corresponding 
disulphides. Carrying out the process in the presence of oxygen (ie. in a 
system open to the atmosphere) results in aroma compounds which may be 
different to those formed by carrying out the process in the absence of 
air (eg. in a system closed to the atmosphere ie. in an autoclave). 
In another embodiment of the invention, there is provided a flavour 
precursor mixture, generating a savoury flavour upon heating, and 
comprising compound X (as defined earlier), cystein and/or a hydrogen 
sulphide donor. 
Such flavour precursor mixtures are very useful because the flavour is 
developed upon heating of the foodstuff to which the precursor mixture is 
added. Such heating is often done only a few minutes before the foodstuff 
is ingested so that flavour degeneration and flavour losses are kept to a 
minimum. However, when aqueous systems are involved lower conversions into 
flavour compounds may occur and an appropriately higher level of the 
flavour precursor mixture may be required. The use of such flavour 
precursor mixtures can also be useful in dry soup mixes and canned meat 
products, where the flavour is developed upon sterilizing the closed cans. 
Sometimes it is advantageous to have heated the flavour precursor mixture 
under mild conditions before incorporating it in a foodstuff; some of the 
precursor mixture is then already converted into flavour compounds and at 
the same time the flavour precursor mixture is still present to develop 
the full flavour at a later stage. 
The flavours and flavour precursor mixtures according to the invention may 
be added to products to be flavoured, either as such, or as part of a 
flavouring composition. The term flavouring composition as used herein 
means a mixture of flavours or flavour components, if desired dissolved in 
a suitable solvent or mixed with a powdered substrate or carrier or 
processed to form a powdered product. Such a flavouring composition is 
used to impart a flavour impression to a product or to improve or alter 
the existing flavour impression of a product. 
Thus, in a further embodiment of the invention there is provided a 
flavouring composition comprising flavours and flavour components known in 
the art and in addition one or more flavours obtained by the process of 
the invention and/or flavour precursor mixtures according to the 
invention. 
Examples of products the flavour precursor mixtures according to the 
invention may be added to, either as such or as part of a flavour 
composition, are ingredient mixes for products which are prepared by 
extrusion, frying or baking. 
Flavours or flavour components which may be advantageously combined with 
the flavours or flavour precursor mixtures according to the invention into 
flavouring compositions are: natural products such as extracts, essential 
oils, absolutes, resins, concretes, fruit juices, etc., but also synthetic 
components such as hydrocarbons, alcohols, aldehydes, ketones, esters, 
ethers, acetals, ketals, acids, etc., including saturated and unsaturated 
compounds, aliphatic, alicyclic and heterocyclic compounds. 
Auxiliary substances and solvents which can be used in flavouring 
compositions containing the flavours and flavour precursor mixtures 
according to the invention are, for example: ethanol, isopropanol, 
diethyleneglycol monoethyl ether, glycerol, triacetin etc. Powdered 
substrates or carriers may include salt, starch derivatives and the like. 
Processing into a powdered product may include spray-drying and other 
techniques of micro-encapsulation. 
The savoury flavour mixture of this invention, and/or the flavour precursor 
mixture, can be used in sauces and stock cubes, for example.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention will now be described, by way of example only, with 
reference to the accompanying FIGS. 1, 2, 3 and 4. 
EXAMPLE 1 
104 mmol of 90% 
4-hydroxy-2,5-dimethyl-2-(2-hydroxy-3-oxo-2-butyl)-3(2H)-furanone per kg 
of glycerol and 954 mmol of cysteine per kg of glycerol were added to a 
300 ml autoclave. 
After closing the autoclave to the atmosphere, the total mixture was 
stirred and the air/oxygen was removed by flushing with nitrogen after 
which 644 mmol of hydrogen sulphide gas (15-16 bar) per kg of glycerol was 
added to the autoclave. The amount of gas added was determined by weighing 
the gas cylinder. After addition of the hydrogen sulphide, the autoclave 
was heated to 120.degree. C. 
During the reaction, samples of the reaction mixture were taken from the 
autoclave to determine the formation of flavour compounds. 
The samples of reaction mixture were extracted and then analysed by gas 
chromatography. 
Extraction Procedure 
Approx 2.7 grams of the crude reaction mixture were diluted with approx 7 
grams glycerol, and added to approx 70 ml water. This mixture was 
extracted by means of a mini Likens Nickerson extraction unit (available 
from Chrompack) in 2 ml dichloromethane. To prevent foam formation, 3 
drops of anti-foaming agent were added to the distillation. 
Extraction Conditions 
Solvent: 2 ml dichloromethane 
Cooling cold finger: -1.degree. C. using a cryostat 
Temperature oil bath solvent: 70.degree. C. 
Control unit heating mantle: position 3 (140.degree. C.) 
Extraction time: 5 mins post `initial` solvent reflux 
240 mins extraction 
20 mins `post` solvent reflux 
To determine quantitatively the amount of flavour compounds formed, 
C.sub.12 -methylester was added as an internal standard to the 
dichloromethane extract of the reaction mixture. This internal standard is 
marked 2 in the relevant figures. 
The dichloromethane extract obtained was analysed by gas chromatography 
using the following conditions: 
Gas Chromatograph: Hewlett Packard 5890 series II 
Column: CPsil05-CB,1=25 m, i.d.=0.32 mm, df=1.2 .mu.m 
P.sub.in : 8 psi 
T.sub.injector : 240.degree. C. 
Detection: FID and FPD (HP accessory 19256A) 
T.sub.FID : 260.degree. C. 
T.sub.FPD : 250.degree. C. (range 2) 
oven temperature program: 50.degree. C.--2.5.degree. C./min--250.degree. C. 
The column effluent was split to the two detectors using a splitter at the 
end of the GLC column. 
The injector is split and the split ratio is 1:30 ie. 1 part in 30 of the 
sample enters the column and the rest of the sample is ejected. 
Where: 
CPsil05-CB is the trade name for a 100% dimethylsiloxane chemically bonded 
column available from Chrompack. 
1: length of column 
i.d.: internal diameter of column 
df: thickness of the film of the stationary phase in the column 
P.sub.in : inlet pressure 
T.sub.injector : temperature of split/splitless injector 
FID: Flame Ionisation Detector 
FPD: Flame Photometric detector 
T.sub.FID : Temperature of FID 
T.sub.FPD : Temperature of FPD 
HP: Hewlett Packard 50.degree. C.--2.5.degree. C./min--250.degree. C. means 
that the rate of increase of the temperature of the oven is 2.5.degree. C. 
per min, starting at a temperature of 50.degree. C. and finishing at a 
temperature of 250.degree. C. 
LTP (Linear Temperature Programme) indices were calculated using an alkanes 
mix (C5-C20). 
The yields of the flavour compounds were calculated on the assumption that 
their response factor was 1 compared to the internal standard, and that 
the extraction recovery was 60%. 
FIGS. 1a and 1b are gas chromatographs (FID and FPD respectively) of the 
resultant savoury flavour mixture after a reaction time of 1 hour 
indicating the presence of a number of key flavour compounds, including 
2,5-dimethyl-4-mercapto-3(2H)-thiophenone (yield 0.35%) and 
2,5-dimethyl-4-mercapto-3(2H)-furanone (yield 4.6%). 
After a reaction time of 2 hours, the yields were: 
2,5-dimethyl-4-mercapto-3(2H)-thiophenone 6.4% 
2,5-dimethyl-4-mercapto-3(2H)-furanone 0.4% 
The LTP Index for 2,5-dimethyl-4-mercapto-3(2H)-thiophenone is 1262, and 
the LTP Index for 2,5-dimethy-4-mercapto-3(2H)-furanone is 1120. Their 
peaks are marked 4 and 6 respectively in the figures. 
COMATIVE EXAMPLE A 
95 mmol of 95% 4-hydroxy-2,5-dimethyl-3(2H)-furanone per kg of glycerol and 
954 mmol of cysteine per kg of glycerol were added to a 300 ml autoclave. 
The experimental procedure of Example 1 was followed, except that 686 mmol 
of hydrogen sulphide gas per kg of glycerol was added. 
FIGS. 3a and 3b are gas chromatographs (FID & FPD respectively) of the 
resultant savoury flavour mixture after a reaction time of 1 hour. The 
yield of 2,5-dimethyl-4-mercapto-3(2H)-furanone (6) after 1 hour was 0.4% 
(and after 2 hours was 0.2%). The yield of 
2,5-dimethyl-4-mercapto-3(2H)-thiophenone (4) after 1 hour was 0% (and 
after 2 hours was 1.5%). 
COMATIVE EXAMPLE B 
95 mmol of 95% 4-hydroxy-2,5-dimethyl-3(2H)-furanone per kg of glycerol, 
100 mmol of diacetyl per kg of glycerol and 954 mmol of cysteine per kg of 
glycerol were added to a 300 ml autoclave. The experimental procedure of 
Example 1 was followed, except that 630 mmol of hydrogen sulphide gas per 
kg of glycerol was added. 
FIGS. 4a and 4b are gas chromatographs (FID & FPD respectively) of the 
resultant savoury flavour mixture after a reaction time of 1 hour. The 
yield of 2,5-dimethyl-4-mercapto-3(2H)-furanone (6) was 0.4 after 1 hour 
(and was 0% after 2 hours). The yield of 
2,5-dimethyl-4-mercapto-3(2H)-thiophene (4) was 0% after 1 hour (and 1.3% 
after 2 hours). 
EXAMPLES 2 to 4 
COMATIVE EXAMPLES C TO H 
For examples 2, 3 and 4, the experimental procedure of Example 1 was 
repeated, but using the component amounts and conditions specified in 
Table 1. 
For comparative example C, the experimental procedure of Example 1 was 
repeated, but using the component amounts and conditions specified in 
Table 1 and replacing 
4-hydroxy-2,5-dimethyl-2-(2-hydroxy-3-oxo-2-butyl)-3(2H)-furanone with 
2,5-dimethyl-3(2H)-furanone. This experiment corresponds to example 9 of 
EP 571031. 
For comparative example D, the experimental procedure of Example 1 was 
repeated, but using the component amounts and conditions specified in 
Table 1 and replacing 
4-hydroxy-2,5-dimethyl-2-(2-hydroxy-3-oxo-2-butyl)-3(2H)-furanone with 
2,5-dimethyl-2-(2-hydroxy-3-oxo-2-butyl)-3(2H)-furanone (the diacetyl 
oligomer of EP 571031). This experiment corresponds to example 8 of EP 
571031. 
For examples E, F and G, the experimental procedure of Example 1 was 
repeated, but using the component amounts and conditions specified in 
Table 1 and replacing 
4-hydroxy-2,5-dimethyl-2-(2-hydroxy-3-oxo-2-butyl)-3(2H)-furanone with 
2,5-dimethyl-4-hydroxy-3(2H)-furanone and diacetyl (their adduct 
4-hydroxy-2,5-dimethyl-2-(2-hydroxy-3-oxo-2-butyl)-3(2H)-furanone was not 
formed first so was not present). 
For comparative example H, the experimental procedure of Example 1 was 
repeated, but using the component amounts and conditions specified in 
Table 1, omitting the addition of cystein and replacing 
4-hydroxy-2,5-dimethyl-2-(2-hydroxy-3-oxo-2-butyl)-3 (2H)-furanone with 
2,5-dimethyl-4-hydroxy-3(2H)-furanone. This experiment corresponds to 
example B2 of GB 1283912, although a different ratio of hydrogen sulphide 
to 2,5-dimethyl-4-hydroxy-3(2H)-furanone was used. 
In example 4 and comparative examples G & H, water was used as a medium 
instead of glycerol. 
The temperatures shown in Table 1 are those to which the autoclave was 
heated. 
During the reactions, samples of the reaction mixture were taken from the 
autoclave to determine the formation of flavour compounds using gas 
chromatography, as in example 1. 
RESULTS 
Table 2 shows the flavour compounds found in samples of reaction mixtures 
extracted after reaction times of 1 to 4 hours. These compounds, their 
yields (% and mmol/kg) were analysed by gas chromatography. 
It is evident that comparative examples C and D produced high yields of 
only one key flavour compound, namely 2,5-dimethylfuranthiol. The gas 
chromatograph of comparative example D is shown in FIG. 2: peak 8 is 
2,5-dimethylfuranthiol. 
Comparative example F produced only two key flavour compounds (namely, 
2,5-dimethyl-4-mercapto-3(2H)-furanone and 
2,5-dimethyl-4-mercapto-3(2H)-thiophenone) and in relatively low amounts. 
In comparative examples E, G and H, 2,5-dimethyl-3(2H)-furanone was 
present, together with 2,5-dimethyl-4-mercapto-3(2H)-furanone, 
2,5-dimethyl-4-mercapto-3(2H)-thiophenone and dihydro 2(4 or 
5)-dimethyl-3(2H)-thiophenone (amongst others). However, the yields of 
these flavour compounds were low. 
Experiments 2, 3 and 4 of the present invention provided a wide range of 
key flavour compounds with particularly good yields of 
2,5-dimethyl-4-mercapto-3(2H)-furanone and 
2,5-dimethyl-4-mercapto-3(2H)-thiophenone. Experiment 2 provided the best 
results; from this it can be concluded that the present invention is 
preferably carried out at 100.degree. C. in glycerol, rather than at 
120.degree. C. or in water. 
TABLE I 
__________________________________________________________________________ 
mmol/kg 
example C D E 2 3 F G 4 H 
medium glycerol 
glycerol 
glycerol 
glycerol 
glycerol 
glycerol 
water 
water 
water 
temperature (degrees C.) 
120 120 100 100 120 120 100 
100 
100 
__________________________________________________________________________ 
cysteine 965 967 968 996 968 990 974 
970 
hydrogensulfide 428 428 597 581 611 634 429 
441 
457 
2,5-dimethyl-3(2H)-furanone 
130 
diacetyl oligomer 125 
2,5-dimethyl-4-hydroxy-3(2H)-furanone 
100 101 101 101 
diacetyl 102 101 102 
fupre2 110 100 102 
__________________________________________________________________________ 
fupre2 = 4hydroxy-2,5-dimethyl-(2-hydroxy-3-oxo-2-butyl)-3(2H)-furanone 
diacetyl oligomer = 2,5dimethyl-2-(2-hydroxy-3-oxo-2-butyl)-3(2H)-furanon 
mmol/kg = mmol per kg of medium 
TABLE 2 
__________________________________________________________________________ 
yield [%] mmol/kg 
reaction time [hours] 
reaction time [hours] 
example 1 2 3 4 1 2 3 4 
__________________________________________________________________________ 
C 2,5-dimethylfuranthiol 
2.2 
6.7 
9.4 
8.3 
2.9 
8.7 
12.2 
10.8 
D 2,5-dimethylfuranthiol 
31.7 
25 18.2 
9.7 
39.4 
31.1 
22.6 
12.1 
E 2,5-dimethyl-4-mercapto-3(2H)-furanone 
0.03 
0.40 
0.62 
0.42 
0.03 
0.40 
0.63 
0.42 
2,5-dimethyl-4-mercapto-3(2H)-thiophenone 
0.00 
0.00 
0.03 
0.04 
0.00 
0.00 
0.00 
0.00 
2,5-dimethylfuranthiol 
0.00 
0.00 
0.04 
0.02 
0.00 
0.00 
0.04 
0.02 
dihydro 2(4 or 5)-dimethyl-3(2H)-thiophenon 
0.08 
0.20 
0.34 
0.52 
0.08 
0.20 
0.34 
0.52 
2,5-dimethyl-3(2H)-furanon 
0.06 
0.09 
0.10 
0.13 
0.06 
0.09 
0.10 
0.13 
2,5-dimethyl-4-hydroxy-3(2H)-thiophenone 
0.00 
0.00 
0.00 
0.00 
0.00 
0.00 
0.00 
0.00 
2,5-dimethyl-3-mercaptothiophene 
0.00 
0.05 
0.07 
0.06 
0.00 
0.05 
0.08 
0.06 
2,5-dimethyl-3(2H)-thiophenone 
0.00 
0.00 
0.00 
0.00 
0.00 
0.00 
0.00 
0.00 
2 2,5-dimethyl-4-mercapto-3(2H)-furanone 
7.05 
10.06 
8.61 
8.32 
7.00 
10.00 
8.55 
8.27 
2,5-dimethyl-4-mercapto-3(2H)-thiophenone 
0.12 
0.46 
0.91 
1.49 
0.08 
0.34 
0.78 
1.41 
2,5-dimethylfuranthiol 
0.03 
0.09 
0.11 
0.16 
0.03 
0.09 
0.11 
0.16 
dihydro 2(4 or 5)-dimethyl-3(2H)-thiophenon 
0.06 
0.15 
0.23 
0.33 
0.06 
0.15 
0.23 
0.32 
2,5-dimethyl-3(2H)-furanon 
0.15 
0.26 
0.31 
0.40 
0.15 
0.25 
0.31 
0.40 
2,5-dimethyl-4-hydroxy-3(2H)-thiophenone 
0.02 
0.04 
0.06 
0.07 
0.02 
0.04 
0.06 
0.07 
2,5-dimethyl-3-mercaptothiophene 
0.02 
0.03 
0.03 
0.05 
0.02 
0.03 
0.03 
0.05 
2,5-dimethyl-3(2H)-thiophenone 
0.00 
0.01 
0.03 
0.05 
0.00 
0.01 
0.03 
0.05 
3 2,5-dimethyl-4-mercapto-3(2H)-thiophenone 
0.41 
5.04 
n.d 
0.47 
0.35 
5.12 
n.d 
0.48 
2,5-dimethylfuranthiol 
0.05 
0.28 
n.d 
0.06 
0.05 
0.28 
n.d 
0.06 
dihydro 2(4 or 5)-dimethyl-3(2H)-thiophenon 
0.14 
0.03 
n.d 
0.30 
0.14 
0.03 
n.d 
0.3 
2,5-dimethyl-3(2H)-furanon 
0.18 
0.35 
n.d 
0.25 
0.18 
0.35 
n.d 
0.25 
2,5-dimethyl-4-hydroxy-3(2H)-thiophenone 
0.01 
0.13 
n.d 
0.68 
0.01 
0.12 
n.d 
0.68 
2,5-dimethyl-3-mercaptothiophene 
0.02 
0.29 
n.d 
0.60 
0.02 
0.29 
n.d 
0.6 
2,5-dimethyl-3(2H)-thiophenone 
0.01 
0.58 
n.d 
1.21 
0.01 
0.58 
n.d 
1.21 
F 2,5-dimethyl-4-mercapto-3(2H)-furanone 
0.36 
0.09 
0.00 
0.00 
0.35 
0.09 
0.00 
0.00 
2,5-dimethyl-4-mercapto-3(2H)-thiophenone 
0.03 
1.15 
1.88 
0.68 
0.03 
1.11 
1.81 
0.65 
G 2,5-dimethyl-4-mercapto-3(2H)-furanone 
0.51 
1.20 
1.47 
2.25 
0.51 
1.21 
1.48 
2.27 
2,5-dimethyl-4-mercapto-3(2H)-thiophenone 
0.02 
0.04 
0.04 
0.08 
0.01 
0.01 
0.03 
0.04 
2,5-dimethylfuranthiol 
0.00 
0.03 
0.03 
0.07 
0.00 
0.03 
0.03 
0.07 
dihydro 2(4or 5)-dimethyl-3(2H)-thiophenon 
0.03 
0.06 
0.10 
0.13 
0.03 
0.06 
0.10 
0.13 
2,5-dimethyl-3(2H)-furanon 
0.02 
0.06 
0.13 
0.21 
0.02 
0.06 
0.13 
0.22 
2,5-dimethyl-4-hydroxy-3(2H)-thiophenone 
0.02 
0.01 
0.01 
0.02 
0.02 
0.01 
0.01 
0.02 
2,5-dimethyl-3-mercaptothiophene 
0.02 
0.03 
0.03 
0.04 
0.02 
0.03 
0.03 
0.04 
2,5-dimethyl-3(2H)-thiophenone 
0.00 
0.00 
0.00 
0.00 
0.00 
0.00 
0.00 
0.00 
4 2,5-dimethyl-4-mercapto-3(2H)-furanone 
3.25 
3.29 
3.39 
3.72 
3.30 
3.35 
3.45 
3.79 
2,5-dimethyl-4-mercapto-3(2H)-thiophenone 
0.01 
0.06 
0.09 
0.13 
0.01 
0.03 
0.06 
0.08 
2,5-dimethylfuranthiol 
0.00 
0.02 
0.05 
0.10 
0.00 
0.02 
0.05 
0.11 
dihydro 2(4 or 5)-dimethyl-3(2H)-thiophenon 
0.03 
0.07 
0.09 
0.12 
0.03 
0.07 
0.09 
0.12 
2,5-dimethyl-3(2H)-furanon 
0.25 
0.39 
0.50 
0.71 
0.20 
0.40 
0.51 
0.72 
2,5-dimethyl-4-hydroxy-3(2H)-thiophenone 
0.00 
0.00 
0.01 
0.02 
0.00 
0.00 
0.01 
0.02 
2,5-dimethyl-3-mercaptothiophene 
0.00 
0.03 
0.03 
0.05 
0.00 
0.03 
0.03 
0.05 
2,5-dimethyl-3(2H)-thiophenone 
0.00 
0.00 
0.00 
0.00 
0.00 
0.00 
0.00 
0.00 
H 2,5-dimethyl-4-mercapto-3(2H)-furanone 
0.61 
1.09 
1.34 
1.76 
0.62 
1.10 
1.35 
1.78 
2,5-dimethyl-4-mercapto-3(2H)thiophenone 
0.05 
0.16 
0.29 
0.44 
0.02 
0.09 
0.20 
0.32 
2,5-dimethylfuranthiol 
0.00 
0.00 
0.00 
0.00 
0.00 
0.00 
0.00 
0.00 
dihydro 2(4 or 5)-dimethyl-3(2H)-thiophenon 
0.00 
0.00 
0.05 
0.07 
0.00 
0.00 
0.05 
0.07 
2,5-dimethyl-3(2H)-furanon 
0.04 
0.05 
0.06 
0.07 
0.04 
0.05 
0.06 
0.07 
2,5-dimethyl-4-hydroxy-3(2H)-thiophenone 
0.03 
0.12 
0.17 
0.25 
0.03 
0.12 
0.17 
0.25 
2,5-dimethyl-3-mercaptothiophene 
0.00 
0.00 
0.00 
0.00 
0.00 
0.00 
0.00 
0.00 
2,5-dimethyl-3(2H)-thiophenone 
0.00 
0.00 
0.02 
0.03 
0.00 
0.00 
0.02 
0.03 
__________________________________________________________________________ 
n.d = not detected 
mmol/kg = mmol per kg of medium 
EXPERIMENT 5 
8.3 g of 4-hydroxy-2,5-dimethyl-3(2H)-furanone, 7.9 g of butanal, 0.2 g of 
oxalic acid and 19.4 g of water were reacted at room temperature to form 
an adduct of 4-hydroxy-2,5-dimethyl-3(2H)-furanone and butanal. High 
Performance Liquid Chromatography was used to confirm the presence of this 
adduct. 
0.5 g of cysteine, 1.0 g diacetyl, 49.3 g glycerol and 1.9 g of water were 
added to 11.5 g of the adduct and heated in an open system at 100.degree. 
C. for one hour. The reaction products were isolated by Likens Nickerson 
distillation and analysed by Gas Liquid Chromatography, as in example 1. 
EXPERIMENT 6 
7.3 g of 4-hydroxy-2,5-dimethyl-3(2H)-furanone, 6.9 g of 2,3-pentanedione, 
0.2 g of oxalic acid and 20.3 g of water were reacted at room temperature 
to form an adduct of 4-hydroxy-2,5-dimethyl-3(2H)-furanone and 
2,3-pentanedione. High Performance Liquid Chromatography was used to 
confirm the presence of this adduct. 
0.5 g of cysteine, 1.0 g diacetyl, 49.3 g glycerol and 1.9 g of water were 
added to 4.3 g of the adduct and heated in an open system at 100.degree. 
C. for one hour. The reaction products were isolated by Likens Nickerson 
distillation and analysed by Gas Liquid Chromatography, as in example 1. 
COMATIVE EXAMPLE I 
8.0 g of 4-hydroxy-2,5-dimethyl-3(2H)-furanone, 0.5 g of cysteine, 1.0 g of 
diacetyl, 49.3 g of glycerol and 1.9 g of water were heated together in an 
open system at 100.degree. C. for one hour. The reaction products were 
isolated by Likens Nickerson distillation and analysed by Gas Liquid 
Chromatography, as in example 1. 
RESULTS 
The yields of 2,5-dimethyl-4-mercapto-3(2H)-furanone were as follows: 
example 5=0.2% 
example 6=0.3% 
comparative example I=0.02%. 
FLAVOUR DESCRIPTION 
2,5-dimethyl-4-mercapto-3(2H)-furanone is sweet, onion-like, meaty, full 
flavour. 
SUMMARY 
In closed systems, the experiments of Examples 1 to 4 resulted in better 
yields of certain key flavour compounds (particularly 
2,5-dimethyl-4-mercapto-3(2H)-furanone) than the experiments of 
Comparative Examples A to H. 
In open systems, the experiments of Example 5 and 6 also resulted in better 
yields of 2,5-dimethyl-4-mercapto-3(2H)-furanone than the experiment of 
Comparative Example I. However, the yields of this flavour compound were 
considerably lower using an open system rather than a closed system.