Aspartame stabilization with cyclodextrin

The present invention deals with the stabilization of aspartame, by the formation of an inclusion complex of aspartame and cyclodextrin. The inclusion complex is formed by combining the aspartame with the cyclodextrin in a medium suitable for formation of the inclusion complex before a substantial degree of hydrolysis of the aspartame can occur. Upon drying a dry inclusion complex is formed.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention deals with artificial sweeteners. 
2. Description of the Art Practices 
In recent years suitable substitutes for saccharin and cyclamates have been 
sought due to potential health consequences of overuse of these 
sweeteners. 
Aspartame has been suggested as a replacement for all artificial sweeteners 
due to its sweetening properties and purported low toxicity levels. The 
use of aspartame is described in a bulletin of G.D. Searle & Co. through 
its subsidiary Searle Food Resources, Inc., Box 1045, Skokie, Ill. 60076 
in an article entitled THE NUTRASWEET BREAKTHROUGH, Copyright 1982, 
Publication No. US 001-682 which is incorporated by reference. A portion 
of the publication indicates that aspartame loses its effectiveness due to 
breakdown of the components under conditions where hydrolysis may occur, 
particularly in the acid pH region. Further discussions of aspartame under 
the title ASTAME CLEARED FOR SOFT DRINKS was recently published at page 
41 of the Food Chemical News, Vol. 25, No. 17 (July 4, 1983) which is a 
publication of Food Chemical News, Inc., 1101 Pennsylvania Avenue, S.E., 
Washington, D.C. 20003. The Food Chemical News article is also herein 
incorporated by reference. 
The chemistry of cyclodextrin compounds is discussed in an article entitled 
CYCLODEXTRIN INCLUSION COMPOUNDS IN RESEARCH AND INDUSTRY by Wolfram 
Saenger at pages 344-362 of the publication ANGEW. CHEM. INT. ED. ENGL., 
Vol. 19 (1980). A further discussion of cyclodextrins is found in an 
article entitled FORMATION AND MOLECULAR DYNAMICS OF CYCLOAMYLOSE 
INCLUSION COMPLEXES WITH PHENYLANINE by Inoue and Miyata in the Bull. 
Chem. Soc. Jpn. Vol. 54, pages 809-816 (1981). Both of the aforementioned 
articles on cyclodextrins are herein incorporated by reference. 
Japanese patent publication No. 56-2560 teaches and describes the use of 
beta-cyclodextrin in combination with a variety of sweetners including 
aspartame in order to produce a water-soluble solid sweetener. This 
publication indicates that by using beta-cyclodextrin in combination with 
sweeteners such as aspartame, that a water-soluble solid sweetener can be 
prepared which has desirable properties such as resistance to wear and 
tear. This reference also indicates that the solid sweeteners prepared by 
combining beta-cyclodextrin with other sweeteners are easily dissolved in 
water, easily tabletized or shaped, having excellent smoothness and 
crumbling properties. Thus, beta-cyclodextrin is used in this reference as 
a bulking agent for the preparation of a solid tabletized sweetener. 
Maruzen teaches that such solid sweeteners can be prepared by mixing and 
molding. The sweetener can then be transported or added into water for 
sweetening purposes. 
It has now been discovered that cyclodextrin can be combined with aspartame 
under conditions which result in the stabilization of aspartame against 
hydrolysis. It is thus an object of the instant invention to describe a 
composition of matter containing aspartame in a specific structural 
relationship with cyclodextrin (an inclusion complex) which serves to 
reduce hydrolysis and gives more stability to the aspartame. A further 
object of the instant invention is to provide a method whereby the 
protection of aspartame against hydrolysis can be optimized. A further 
object of the instant invention is to describe a method for producing the 
inclusion complex of cyclodextrin and aspartame in a solid form which 
preserves the aspartame under adverse storage conditions such as heat, 
humidity, light, and acidity. Other objects will become apparent as this 
description proceeds. 
SUMMARY OF THE INVENTION 
The invention describes a method of stabilizing aspartame from hydrolysis 
including the steps of combining aspartame and a member selected from the 
group consisting of: 
(a) alpha-cyclodextrin; 
(b) beta-cyclodextrin; 
(c) gamma-cyclodextrin; and, 
(d) mixtures of the above, 
wherein the combining is conducted prior to a substantial degree of 
hydrolysis of the aspartame. The aspartame and the cyclodextrin are 
combined in a medium suitable for the formation of the inclusion complex. 
The inclusion complex then forms. 
Also, described is a composition including aspartame and a member selected 
from the group consisting of: 
(a) alpha-cyclodextrin; 
(b) beta-cyclodextrin; 
(c) gamma-cyclodextrin; and, 
(d) mixtures of the above. 
The aspartame and the cyclodextrin are present in a dry inclusion complex. 
The process for preparing this dry inclusion complex is also described. 
Further described is a cooked food product including aspartame and a member 
selected from the group consisting of: 
(a) alpha-cyclodextrin; 
(b) beta-cyclodextrin; 
(c) gamma-cyclodextrin; and, 
(d) mixtures of the above. 
Also, described is a food product including aspartame and a member selected 
from the group consisting of: 
(a) alpha-cyclodextrin; 
(b) beta-cyclodextrin; 
(c) gamma-cyclodextrin; and, 
(d) mixtures of the above. 
Throughout the specification and claims, percentages and ratios are by 
weight and temperatures are in degrees Celsius unless otherwise indicated. 
DETAILED DESCRIPTION OF THE INVENTION 
The present invention as previously indicated deals with the manner of 
stabilizing aspartame so that it does not degrade into its components or 
unwanted by-products. This invention enables aspartame to retain a longer 
shelf life. Stabilization is provided, which reduces the formation of the 
unsweet by-products of hydrolysis, by forming an inclusion complex whereby 
aspartame is at least partially included inside the circular structure of 
cyclodextrin. The included aspartame receives protection from hydrolysis 
type reactions which result in the degradation of the aspartame into 
non-sweet compounds. Once this inclusion complex is formed, the 
degradation or hydrolysis of aspartame is considerably reduced, even in 
the most hydrolyzing conditions. 
A primary reason for desiring to avoid the breakdown into by-products is 
that some of the by-products do not have the sweetness characteristics of 
aspartame and thus the amount of aspartame which must be used is greater 
than that which would be used in the absence of degradation. Therefore, a 
substantial cost savings in the use of aspartame can be achieved if the 
aspartame is stabilized. Secondly, to avoid any potential safety 
considerations, the level of degradation products should be minimized. 
The structure of aspartame is shown below. 
##STR1## 
Aspartame is known under the chemical name 
N-L-alpha-aspartyl-L-phenylalanine 1-methyl ester which corresponds to the 
structure given above. While the structure given above is believed to be 
the only practical structure for aspartame which may be utilized for 
sweeteners, it is of course recognized that the aspartame may be obtained 
in the form of derivatives such as salts, i.e. sodium, potassium, calcium, 
magnesium and the like, and that if desired the methyl ester may be 
replaced with other compatible ester groups such as ethyl, propyl or the 
like. Similarily on the phenyl ring substituents such as methyl are also 
possible. For practical purposes, however, the named compound in the 
structure give above is the most important. 
The cyclodextrins with which the present invention is concerned includes 
that shown below as beta-cyclodextrin (Formula II). 
##STR2## 
The structure above corresponds to the preferred element of the present 
invention which is a beta-cyclodextrin which contains seven glucoside 
units. The structure of alpha-cyclodextrin is shown below as Formula III. 
##STR3## 
The structure of gamma-cyclodextrin is identical to beta-cyclodextrin 
except that one additional glucopyranose unit is present in the ring 
giving a total of 8 glucopyranose units. The individual glucopyranose unit 
is shown in the center of Formula II. Gamma-cyclodextrin is shown at 
Formula IV. 
##STR4## 
The cyclodextrins mentioned above are commercially available and may be 
utilized in the present invention without modification. 
In the present invention, as both the cyclodextrin and the aspartame are 
dry ingredients, they may be simply combined in the desired proportions 
and utilized. Because a mere dry blend of cyclodextrin and aspartame will 
lack a medium suitable for the formation of the inclusion complex, the 
aspartame will not form the inclusion complex and be stabilized until the 
blend is added to a liquid medium such as water. Since both hydrolysis and 
stabilization reactions of aspartame begin immediately upon dissolution in 
the liquid medium, some portion of aspartame will be hydrolyzed before 
maximum stabilization by the cyclodextrin can occur. This loss of 
aspartame and subsequent sweetness it imparted to the liquid medium is 
tolerable under some conditions, such as when the product containing the 
cyclodextrin-stabilized aspartame is consumed shortly after its 
preparation, or if the liquid medium is one in which the rate of 
hydrolysis of aspartame is slow. For optimum stabilization and reduction 
of the hydrolysis reactions of aspartame, a solid composition containing 
the inclusion complex of cyclodextrin and aspartame can be formed. This 
will considerably reduce hydrolysis if the aspartame is then subjected to 
conditions ordinarily causing it. Thus, if such a solid compositions is, 
during storage, subjected to light, hydrolyzing compounds, heat, 
conditions which would ordinarily cause hydrolysis such as substances 
having a pH in excess of 6 and/or acid, the aspartame will be stabilized 
and its degradation will be considerably reduced. Such stabilization can 
be maximized by using large amounts of cyclodextrin relative to the 
aspartame. 
While the aspartame is not particularly unstable, i.e. leading to 
degradation or hydrolysis products, when it is in the dry state, it is 
desirable to obtain a convenient mixture of the aspartame and cyclodextrin 
so that such may be shipped to any convenient point for manufacture. 
Although this is not a preferred embodiment of the instant invention, a 
mere admixture of aspartame and cyclodextrin will, to an extent, stabilize 
the aspartame and decrease hydrolysis in that when such an admixture is 
subjected to the hydrolyzing conditions a liquid such as water, the 
protective complex will form. For instance, a dry mixture of the 
cyclodextrin and aspartame may be shipped to a bottling plant in a remote 
corner of the world and thereafter used as a stabilized sweetening system 
for a soft drink. It is of course also possible to prepare the blend of 
cyclodextrin and aspartame in a liquid such as water or other medium. The 
presence of heat, acidic conditions and the water can lead to degradation 
of the aspartame. 
The cyclodextrin has been found to stabilize the aspartame and to extend 
the useful life of aspartame containing products. However, the aspartame 
will at some point degrade under the above described condition. Therefore, 
the most practical manner of handling the product is as a powdered 
concentrate so that the aspartame is as active as possible when first 
introduced to degrading conditions. In this manner, the aspartame is in a 
highly divided state which will allow it to dissolve more easily and also 
increase the contact with cyclodextrin so that the inclusion complex can 
form. A more effective and preferred method of extending the useful life 
of aspartame, however, and one which is even more practical for 
safeguarding aspartame against degrading conditions during storage, is to 
prepare the dry inclusion complex. 
The inclusion complex can be formed by combining aspartame and cyclodextrin 
in a medium suitable for the formation of the inclusion complex. A 
suitable medium is a liquid that will solubilize both aspartame and 
cyclodextrin. When dissolved in such a liquid, a portion of the dissolved 
aspartame concentration will become inserted into the cyclodextrin ring, 
thus forming the inclusion complex. After this occurs within the liquid 
medium, the mixture can be dried to leave the inclusion complex. Any 
drying technique which will succeed in removing the liquid medium from the 
aspartame cyclodextrin mixture is acceptable. Preferred drying methods 
will apply such drying techniques as: spray-drying, freeze-drying, heat, 
and/or low pressure. 
The aspartame is degraded or hydrolyzed to aspartyl-phenylalanine, 
phenylalanine, methanol, aspartic acid, and diketopiperazine. Thus, any 
substantial amounts of these materials or their derivatives in addition to 
those present from the manufacturer of aspartame are to be minimized in 
accordance with the invention. 
The aspartame and the cyclodextrin may be combined in any convenient 
proportions. That is, the aspartame will be stabilized even by very small 
amounts of the cyclodextrin. Thus, even very small amounts of cyclodextrin 
relative to the aspartame will allow the formation of some amount of the 
inclusion complex and will afford some protection and stabilization from 
hydrolysis. Large concentrations of the cyclodextrin, however, will favor 
the formation of the inclusion complex and will give greater and more 
optimized stabilization from aspartame hydrolysis. In accordance with the 
instant invention, it is therefore preferred to use cyclodextrin in a 
larger concentration than the aspartame. 
The presence of water or a suitable medium is necessary for the inclusion 
complex to be formed between the aspartame and the cyclodextrin. A 
suitable medium allows the formation of the inclusion complex between the 
aspartame and the cyclodextrin. Any liquid which can dissolve both 
cyclodextrin and the aspartame is a suitable medium. Such liquids can, in 
the drying step, be removed to a substantially complete degree if desired. 
A substantially complete drying will be most preferred under particular 
circumstances, for example, when a long storage period is contemplated 
when reuse as a sweetener for food is contemplated or when media other 
than water or aqueous ethanol are used. Suitable media include water, an 
aqueous mixture of alcohols, or aqueous mixtures of alcohols such as 
aqueous methanol, aqueous ethanol and aqueous isopropanol. Acceptably such 
liquid media can be removed in the drying step to a moisture content level 
of less than 8% by wt. 
It is preferred that the cyclodextrin be present in amounts greater than 
the aspartame as this favors formation of the inclusion complex. It is 
feasible to formulate the product such that the weight ratio of the 
aspartame to the cyclodextrin is from about 5:1 to about 1:200; 
conveniently from about 2:1 to about 1:150; preferably from about 3:2 to 
about 1:100 and most preferably from about 1:1 to about 1:9. A highly 
desirable ratio of the aspartame to cyclodextrin is about 1:3 by weight. 
Weight ratios which tend to optimize the formation of the inclusion 
complex by having an excess of the cyclodextrin and which are thus 
preferred are from about 1.1:1 to about 200:1 of cyclodextrin to 
aspartame, from about 1.1 to about 150:1 and from about 1.1:1 to about 
100. 
As long as the liquid medium used is capable of dissolving both aspartame 
and cyclodextrin, the inclusion complex will form. It is possible to add 
varying excess amounts of cyclodextrin and/or aspartame so that either the 
aspartame or the cyclodextrin or both are present in the liquid medium, 
both as a solid or in its dissolved state. Thus it is possible to prepare 
a solution containing the inclusion complex wherein either all of the 
aspartame is dissolved, and the cyclodextrin is both dissolved and solid, 
or a solution wherein the aspartame is both dissolved and solid and the 
cyclodextrin is dissolved, although the latter would not maximize 
aspartame stability. The type of slurry where the cyclodextrin is both 
dissolved and solid, is highly advantageous to the formation of the 
inclusion complex. It is also possible to form a slurry wherein both the 
aspartame and the cyclodextrin are present in such large amounts that both 
are present in solid form. In any of these cases, the solution or the 
slurries can be dried to give a composition containing the inclusion 
complex. In this included form, the aspartame is stabilized against 
hydrolysis, and if such a composition is subjected to conditions which 
ordinarily cause hydrolysis of aspartame, the degradation of the aspartame 
is reduced. 
The reduction of aspartame hydrolysis is illustrated in Example 4 which 
shows the extended half-life of aspartame in an aqueous solution. The 
importance of stabilizing aspartame against hydrolysis is even more 
appreciated by realizing that aspartame is most unstable at the very pH 
ranges which occur in food products, namely below 3 and over 5.5. 
Since the stabilization of aspartame is important when using aspartame as a 
food sweetener, it is important to optimize this stabilization. Most 
preferably, therefore, the aspartame is stabilized by the formation of the 
inclusion complex before its addition to food products. Although in 
certain instances a food product can act as a medium which would allow the 
formation of the inclusion complex, such a medium also contains other 
materials which might inhibit the formation of the inclusion complex, and 
which would tend to disperse the aspartame instead of allowing the 
proximity of the aspartame to the cyclodextrin in order to form the 
complex. Such food substances would also, due to the presence of 
hydrolyzing materials and adverse pH conditions, tend to encourage or 
cause hydrolysis of the aspartame at the same time. In accordance with the 
instant invention, it is therefore preferred to form the inclusion complex 
before addition to such food substances. This can be achieved either by 
combining the aspartame and the cyclodextrin in a suitable medium such as 
water which can then be added to the food substance in the proper amount, 
or the dry inclusion complex can be formed which will then allow its 
measured addition to the food substance. In either case, stabilization is 
optimized by the preformation of the inclusion complex; stabilization is 
even more optimized under such conditions when cyclodextrin is in excess. 
Where desired the addition of the aspartame to the cyclodextrin may take 
place in water. Water is used in the broadest sense of the term in that 
the mixing could be done in a bottling plant and thus ingredients other 
than the water, aspartame, and cyclodextrin may be present. 
The amount of water in the product is simply that amount used normally. 
Therefore, as a general guideline the water content to the aspartame will 
be from about 10,000:1 to about 1:13. 
The method and composition of the present invention may be used in any of 
the conventional areas where aspartame would be used alone. The products 
of the present invention are particularly useful in those areas where the 
aspartame would be subjected to elevated temperatures and/or acidic 
conditions. All manner of food products, beverages and table sweeteners 
are suggested utilities of the present invention. The present invention 
may also include natural sugars such as sucrose, glucose or fructose with 
the aspartame where the total absence of natural sugars is not required. 
The cyclodextrin is itself naturally sweet and therefore, may enhance the 
quality of the product. 
The effectiveness of the present invention is demonstrated by measuring at 
various times for the presence of aspartame. The use of cyclodextrins and 
in particular the preferred beta-cyclodextrin demonstrates that the 
aspartame is not substantially hydrolyzed and therefore should be without 
substantial loss of sweetening ability. The hydrolysis products of 
aspartame are minimized when compared to similar products in which the 
cyclodextrin is omitted. The cyclodextrins have not been found to 
substantially affect the taste of a product containing aspartame. 
The following are suggested exemplifications of the present invention.

EXAMPLE I 
Part A 
A mixture of aspartame in the form N-L-alpha-aspartyl-L-phenylalanine 
1-methyl ester and beta-cyclodextrin is obtained by adding 1 part of the 
aspartame and 3 parts of beta-cyclodextrin together. These materials are 
then thoroughly combined in a Waring blender to give a finely divided 
powder. 
The product obtained from this Example is useful as a dried powder which 
may be shipped to remote bottling plants for combination of the remaining 
ingredients necessary to prepare a soft drink. This Example is repeated 
using first, alpha-cyclodextrin, and then gamma-cyclodextrin with similar 
results. Mixtures of alpha and gamma, alpha and beta, beta and gamma, and 
then all three cyclodextrins in equal parts also give similar results. 
Example I may be modified by adding 5 parts of the mixture of aspartame and 
beta-cyclodextrin described above with 1 part of sucrose to obtain a table 
sweetener. 
The presence of beta-cyclodextrin in this dry blend will stabilize the 
aspartame from hydrolysis when this contacts water, or an ordinarily 
hydrolyzing medium by forming the inclusion complex. 
Part B 
For superior stabilization, however, and to increase storage life, the dry 
blend of Part A is slurried in water to allow beta-cyclodextrin and 
aspartame to form the inclusion complex. This slurry is then dried by 
using a vacuum removal of water, and/or the application of heat, thereby 
leaving the inclusion complex in its dried form. 
EXAMPLE II 
Aspartame in the form described in Example I, Part A, and beta cylcodextrin 
are combined in a weight ratio of 1 part to 3 parts. 
The mixture above is dissolved in 800 parts water. One portion of the 
aqueous mixture is used to prepare a soft drink by adding a flavoring 
syrup. 
The second portion is obtained as the dry inclusion complex by spray-drying 
the sample to a moisture content of 8%. The inclusion complex may also be 
obtained by freeze-drying the aqueous mixture to 8%. 
The products will be observed to retain stability when exposed to 
conditions favoring hydrolysis of the aspartame. 
EXAMPLE III 
Part A 
A cake mix is prepared using the aspartame and beta-cyclodextrin mixture of 
Example I as the replacement for sucrose. A cake is baked according to the 
above at a temperature of 175.degree. C. without loss of sweet taste. Some 
stabilization occurs when a dry blend as described in Example I, Part A, 
is added to the cake mix. This stabilization is not maximum, however, 
since other cake ingredients hinder the formation of the inclusion complex 
before aspartame hydrolysis. 
Part B 
A cake mix is prepared using aspartame and beta-cyclodextrin product from a 
process as described in Example I, Part B, as the replacement for sucrose. 
Aspartame stabilization in this cake mix is superior over the cake mix 
prepared in Part A of this Example since preformation of the inclusion 
complex optimizes the protection of the aspartame from hydrolysis. 
Part C 
Similarly, a pudding is formulated as above, and cooked at 100.degree. C. 
with the sweetener value maintained. Some stabilization occurs when the 
aspartame and the cyclodextrin dry blend is described in Example I, Part 
A, is added to the pudding. This stabilization is not maximum, however, 
since other pudding ingredients hinder the formation of the protective 
inclusion complex. 
Part D 
A pudding is prepared using an aspartame and beta-cyclodextrin product from 
a process as described in Example I, Part B as the replacement for 
sucrose. Aspartame stabilization in this pudding is superior over the 
pudding prepared from the dry blended aspartame and beta-cyclodextrin of 
Example I, Part A, since preformation of the inclusion complex optimizes 
the protection of the aspartame from hydrolysis. 
Part E 
A gelatin is formulated by using the above sweetner and heating the product 
to 80.degree. C. without losing sweetner value. Some stabilization occurs 
when the sweetner is prepared as described in Example I, Part A. This 
stabilization, however, is not a maximum since some hydrolysis occurs 
before hinder the formation of the protective inclusion complex. 
Part F 
A gelatin is prepared using an aspartame and beta-cyclodextrin product as 
described in Part B, Example I, as the replacement for sucrose. Aspartame 
stabilization in this gelatin is superior over the gelatin prepared from 
the dry-blended aspartame and beta-cyclodextrin of Part A, Example I, 
since preformation of the inclusion complex optimizes protection of the 
aspartame from hydrolysis. 
EXAMPLE IV 
Five sets of aqueous solutions having 2 solutions per set were prepared at 
the pH values listed below. Each set had one solution containing 5 
millimoles (mM) of aspartame (Asp) and another solution with both 5 mM of 
Aspartame, and 10 mM of beta-cyclodextrin (.beta.-CD). The hydrolysis of 
the aspartame in each solution was measured using high performance liquid 
chromatography (HPLC). The temperature of all of the solutions was 
maintained at 55.degree. C. The results are given in terms of aspartame 
half life; and the percent stability improvement realized by the presence 
of the beta-cyclodextrin is given in terms of percent stability 
improvement for each set of solutions in the table below. 
TABLE 
______________________________________ 
Temp. t 1/2 % Stability 
Set Solutions pH (.degree.C.) 
(Hrs) Improvement 
______________________________________ 
1 Asp 2 55 71 
Asp & .beta.-CD 
2 55 93 31 
2 Asp 3 55 158 
Asp & .beta.-CD 
3 55 214 35 
3 Asp 3 55 156 
Asp & .beta.-CD 
3 55 195 25 
4 Asp 5 55 508 
Asp & .beta.-CD 
5 55 590 16 
5 Asp 6 55 3.0 
Asp & .beta.-CD 
6 55 4.0 33 
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