Starch derivatives forming reversible gels

Starch derivatives capable of forming reversible gels are provided. Aqueous dispersions or solutions of the derivatives form thermally reversible hot gels at temperatures above 70.degree. C. and a pH of 3-8, in addition to exhibiting substantial increases in viscosity upon cooling from 95.degree. to 70.degree. C. The starch derivative may be alkali gelatinized at a pH 13 or above and the gel formed at a pH of from 1-10. The gelling agents are starch ethers or starch esters having an amylose content of at least 17% by weight with the ether or ester substituent comprising a linear saturated or unsaturated hydrocarbon chain of at least 12 carbon atoms.

BACKGROUND OF THE INVENTION 
This invention relates to starch derivatives which form reversible gels, 
some of which form hot gels. 
In many compositions, especially those of food systems, starches are often 
employed in order to provide a gel texture to the composition. Unless the 
starch is used in a pregelatinized form, the starchcontaining composition 
must be cooked to effect gelatinization of the starch granules and then 
cooled, usually for a period of 12 to 24 hours at room temperature, in 
order to allow gel formation to occur. 
It is well known that starch is composed of two fractions, the molecular 
arrangement of one being linear and the other being branched. The linear 
fraction of starch is known as amylose and the branched fraction as 
amylopectin. Gel formation is attributed to the retrogradation of the 
amylose portion of starch. After gelatinization and upon cooling, the 
linear chains become oriented in parallel alignment due to the affinity of 
the chain hydroxyl groups for one another. The hydroxyl groups form 
associations through hydrogen bonds and the chains are thus bound together 
forming aggregates which are insoluble in water. In dilute aqueous systems 
the retrograded starch will precipitate while concentrated solutions or 
dispersions of the retrograded starch will form a gel. It is well known 
that phase transformation of a starch gel to a flowable liquid upon 
heating and reformation of the gel upon cooling are not often readily 
achieved. Starch gels which require little or no shear in order to melt 
upon heating are referred to as being thermoreversible. 
When a thickened amylose-containing composition which does not form a gel 
is desired, a derivatized starch is often employed. By introducing 
substituent groups along the starch chain to interfere with the 
retrogradation process, non-gelling starches are obtained which are 
referred to as being stabilized. Common stabilization modifications may be 
accomplished by esterifying or etherifying some of the hydroxyl groups 
along the starch chain. 
The following references describe various starch ester and starch ether 
preparations. 
U.S. Pat. No. 2,661,349 (issued on Dec. 1, 1953 to Caldwell et al.) is 
directed to the preparation of substituted polysaccharides by reacting 
starch with succinic or glutaric acid anhydrides containing a C.sub.5 
-C.sub.18 substituent group to produce starch acid esters. 
U.S. Pat. No. 2,876,217 (issued on Mar. 3, 1959 to E. Paschall) is directed 
to the preparation of cationic starch ethers by treating starch with the 
reaction product of epihalohydrin and a tertiary amine. The reagent is 
said to contain alkyl or alkenyl radicals which may comprise up to 18 
carbon atoms. 
U.S. Pat. No. Re. 28,809 (issued May 11, 1976 to M. Tessler), which is a 
reissue of U.S. Pat. No. 3,720,663 (issued on Mar. 13, 1973 to M. 
Tessler), is directed to the preparation of starch esters by reacting 
starch with an imidazolide of a C.sub.1 -C.sub.20 monocarboxylic or 
monosulfonic acid. U.S. Pat. No. 4,020,272 (issued on Apr. 26, 1977 to M. 
Tessler) further describes starch esters prepared by reactions of starch 
with N,N'-disubstituted imidazolium salts of C.sub.1 -C.sub.20 
monocarboxylic or monosulfonic acids. 
U.S. Pat. No. 4,387,221 (issued on June 7, 1983 to M. Tessler et al.) is 
directed to the preparation of C.sub.1 -C.sub.22 alkyl or alkenyl 
sulfosuccinate starch half esters. 
There are many food and industrial systems which would benefit by employing 
a body and consistency imparting vehicle, i.e., a thickener, which have 
the ability to form a gel texture rapidly while hot instead of requiring 
the system to cool substantially before gel formation begins. Systems 
which would form a gel without any heating would also be useful in food 
systems which require no cooking. 
Moreover, it would be of considerable importance to provide a gel which is 
easily capable of phase transformation upon cooling or heating in order to 
render subsequent homogeneous incorporation of solid or dissolved 
components to the system. 
There is therefore a need for gelling starches which rapidly form 
reversible gels at room temperature without cooking or at relatively high 
temperatures after cooking. There is also a need for gelling starches 
which form hot gels after cooking. 
SUMMARY OF THE INVENTION 
The present invention provides an aqueous reversible gelling agent, which 
comprises a water-soluble or water-dispersible starch derivative 
containing an ether or ester substituent group with an at least C.sub.12 
linear hydrocarbon chain, wherein the starch is an unmodified or modified 
starch having an amylose content of at least 17% by weight and the 
modified starch is a lightly derivatized, lightly converted, and/or 
lightly crosslinked starch and wherein the starch is rendered 
water-soluble or water-dispersible by thermal or alkali gelatinization; 
characterized in that a reversible gel is formed by an aqueous solution or 
dispersion of the thermally-gelatinized starch derivative at a pH of about 
3-8 or of the alkali-gelatinized starch at a pH of about 1-10. The gel 
structure can be reversed by reheating the gel at a pH of 3-8 or by 
adjusting the pH to 13 or above. 
In a preferred embodiment, high temperature gels are formed by the 
thermally-gelatinized starch at a pH of about 4-7 and at a temperature 
above 70.degree. C. and below that temperature at which the gel becomes 
thermoreversible, with the aqueous dispersion of the starch derivative 
exhibiting a substantially greater increase in viscosity during cooling 
from 95.degree. to 70.degree. C. than that of a modified or unmodified 
starch without the substituent with the at least C.sub.12 linear 
hydrocarbon chain. 
By the attachment of long linear hydrocarbon substituents onto the starch 
molecule, many non-gelling starch bases including some chemically 
stabilized bases, do become gelling starches, which are in addition high 
temperature gelling starches when the starch is thermally-gelatinized and 
the pH is between about 3-8, preferably 4-6. 
The high temperature gelling starches herein are useful as thickeners in 
food systems where it is desirable to provide a gel texture at 
temperatures significantly above those of conventional gelling starches, 
e.g. 70.degree. C., and moreover, a gel which is thermoreversible in order 
to facilitate easy incorporation of ingredients into a foodstuff after gel 
formation has occurred. 
None of the above references contemplate or disclose the unique high 
temperature gelling properties or the reversible gels possessed by the 
starches described herein. 
The present invention further provides an improved process for preparing 
starch half-acid esters in water which comprises the step of reacting the 
starch under alkaline conditions with a hydrophobic-substituted cyclic 
dicarboxylic acid anhydride in the presence of a phase transfer agent.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The applicable starch bases which may be used in the preparation of the 
high temperature gelling starches herein include those starches which 
contain at least about 17% amylose such as may be derived from sources 
including corn, potato, tapioca, rice, sago, wheat, sorghum, high amylose 
corn and the like. Starches which contain less amylose, such as waxy 
maize, are not applicable herein. Starch flours may also be used as a 
starch source. 
The derivatizing reagents useful in the preparation of the high temperature 
gelling derivatives herein include any etherifying or esterifying reagents 
which possess a linear chain saturated or unsaturated hydrocarbon 
comprising at least 12 carbon atoms. While not wishing to be bound by any 
theory or mechanism, it is currently believed that high temperature gel 
formation and gel reversibility are functions of the ability of the 
covalently bound long linear chain hydrocarbon groups to form complexes 
with the amylose component of starch. In some instances, i.e., when the 
hydrocarbon chain is adjacent to a sterically hindering group such as a 
carboxyl group (in the case when starch half acid esters are prepared) or 
a quaternary alkyl-substituted amine group (when a cationic reagent is 
employed), the length of the hydrocarbon chain required for high 
temperature gel formation will generally comprise at least 14 carbon 
atoms. The increase in the necessary chain length compensates for what is 
believed to be the steric group's hindering effect which limits the length 
of the hydrocarbon chain available for complexation. 
A suitable class of reagents useful for preparing high temperature gelling 
starch esters herein include the imidazolides or N,N'-disubstituted 
imidazolium salts of carboxylic or sulfonic acids such as those described 
in U.S. Pat. No Re. 28,809 and U.S. Pat. No. 4,020,272 (cited previously) 
having the general formula 
##STR1## 
wherein Z is 
##STR2## 
or --SO.sub.2 --, A is a linear chain hydrocarbon of at least 12 carbon 
atoms, R.sup.1 is H or C.sub.1 -C.sub.4 alkyl, R.sup.2 is C.sub.1 -C.sub.4 
alkyl, and X-is an anion. 
Another suitable class of reagents useful herein which produce high 
temperature gelling starch half-acid esters include substituted cyclic 
dicarboxylic acid anhydrides such as those described in U.S. Pat. No. 
2,661,349 (cited previously) having the structure R1 ? 
##STR3## 
wherein R is a dimethylene or trimethylene radical and A' is a linear 
chain hydrocarbon of at least 14 carbon atoms. The di- or trimethylene 
radical may contain other substituent groups such as sulfonic acid or 
lower alkyl (C.sub.1 -C.sub.4) which would not affect the high temperature 
gelling property. 
A third class of reagents useful herein include the etherifying reagents 
described in U.S. Pat. No. 2,876,217 (cited previously) comprising the 
reaction product of an epihalohydrin with a tertiary amine having the 
structure 
##STR4## 
wherein R.sup.3 and R.sup.4 are independantly H or a C.sub.1 -C.sub.4 
alkyl and A.sup.2 is a linear chain hydrocarbon comprising at least 14 
carbon atoms. 
The starch etherification or esterification reactions may be conducted by a 
number of techniques known in the art employing, for example, an aqueous 
reaction medium, an organic solvent medium, or a dry heat reaction 
technique. The gelling starches herein are preferably prepared employing 
an aqueous reaction medium at temperatures between 20.degree. and 
45.degree. C. 
Although an unmodified starch base is preferably employed in the 
preparation of the high temperature gelling starches, some light to 
moderately converted starches prepared by procedures well known to those 
skilled in the art are also useful. It is believed starch molecular weight 
affects the gel forming capabilities of the derivatives herein. It has 
been observed that a gelling starch will exhibit weaker gel formation as 
the degree of conversion of the starch base is increased. Thus, 
unconverted starches having higher molecular weights will be expected to 
provide the most significant gel formation. It has also been observed that 
the maximum degree of conversion (readily determinable by routine 
experimentation) which will still provide an acceptable gelling product is 
dependant upon the starch source and type of long linear chain 
derivatization employed. 
Lightly crosslinked starch bases may also be rendered gelling by the 
methods described herein. The maximum level of crosslinking useful, which 
will vary depending on the starch base, crosslinking agent, and long 
linear chain reagent employed, may be easily determined by routine 
experimentation. 
The present invention is also useful for providing gelling properties to 
starches which contain other functional ionic and non-ionic groups. Of 
considerable importance is the ability of the long linear chain 
hydrocarbon substituents to reverse to some extent the stabilizing effect 
provided by other functional groups on starch. For example, corn starches 
which have been stabilized with propylene oxide to hydroxypropyl degrees 
of substitution of 0.144 or less were made gelling after treatment with 
tetradecenylsuccinic anhydride. The maximum degree of additional 
substitution on the gelling starches herein will be understood to vary 
depending on the starch base and its derivatization as well as the long 
linear chain reagent employed. 
The gelling starches herein may be additionally modified as described above 
at a time either prior to, simultaneously with, or subsequent to reaction 
with the long linear chain hydrocarbon esterifying or etherifying reagent. 
The skilled practitioner will of course recognize that certain starch 
modification reactions that employ conditions which render the long chain 
reagent or gelling derivative unstable must be conducted prior to reacting 
the starch with the long chain reagent. 
Methods for preparing the modified starches herein are well-known to those 
skilled in the art and discussed in the literature. See, for example, R. 
L. Whistler, Methods in Carbohydrate Chemistry, Vol. IV, 1964, pp. 
279-311; R. L. Whistler et al., Starch: Chemistry and Technology, Second 
Edition, 1984, pp. 311-366; and R. Davidson and N. Sittig, Water-Soluble 
Resins, 2nd Ed., 1968, Chapter 2. 
Due to the hydrophobic nature of certain of the long linear chain 
hydrocarbon reagents useful herein (i.e., substituted cyclic dicarboxylic 
acid anhydrides), in standard aqueous reactions, the reagents react with 
starch in only minor amounts, thereby leaving large quantities of residual 
unreacted reagent as an impurity in the final reaction product. 
Furthermore, the aqueous reactions proceed at relatively slow rates, as 
indicated by the amount of caustic consumed over time. 
It has been found that granular starch may be advantageously treated with 
hydrophobic (C.sub.10 or higher) hydrocarbon-substituted cyclic 
dicarboxylic acid anhydrides under mild aqueous reaction conditions (i.e., 
20.degree.-40.degree. C. at a pH of 8) in the presence of at least 5%, 
preferably 7-15% (based on the weight of the reagent), of a phase transfer 
agent. These reactions proceed faster with no visible unreacted reagent 
appearing upon starch recovery. Suitable phase transfer agents useful 
herein include, in general, organic quaternary salts, tertiary amines, and 
polyalkylene oxide ethers or esters. 
The organic quaternary salts useful herein have the general formula 
(AM).sup.+ X.sup.- where A is the organic portion of the salt molecule 
bonded to M by four covalent linkages comprising monovalent or polyvalent 
hydrocarbon radicals having a total sum of at least 10 carbon atoms, M is 
selected from the group consisting of nitrogen, phosphorus, arsenic, 
antimony and bismuth, and X.sup.- is an anion which dissociates from the 
cation (AM).sup.+ under aqueous conditions, preferably selected from the 
group consisting of halogen and hydroxyl anions. The organic salts of 
trioctylmethyl ammonium chloride and Aliquat.RTM. 336 (referred to as 
tricaprylylmethyl ammonium chloride which has a mixture of C.sub.8 
-C.sub.10 hydrocarbon radicals and obtained from General Mills Chemicals) 
are preferably employed. The salts are described in U.S. Pat. No. 
3,992,432 (issued Nov. 16, 1976 to D. Napier et al.), the disclosure of 
which is hereby incorporated by reference. Other useful quaternary organic 
salts include, for example, benzyltriethyl ammonium chloride, 
tetra-n-butyl ammonium chloride, n-hexadecyltrimethyl ammonium bromide, 
n-hexadecyl pyridinium bromide, n-hexadecyl-tri-n-butyl phosphonium 
bromide, tetra-n-octyl ammonium bromide, and tridecylmethyl ammonium 
chloride. 
The tertiary amines useful herein as phase transfer agents should also 
posses hydrocarbon radicals having a total sum of at least 10 carbon 
atoms. Typical tertiary amines include, for example, octyldimethylamine 
and didecylmethylamine. 
The polyalkylene oxide ethers and esters useful herein as phase transfer 
agents may include, for example, polyoxyethylene (4) sorbitan monolaurate, 
polyoxyethylene (4) sorbitan monostearate, polyoxyethylene (8) stearate, 
polyoxyethylene (4) lauryl ether, and polyoxyethylene (4) nonylphenyl 
ether. 
In addition to yielding gels at high temperatures, the starch derivatives 
herein also exhibit rapid viscosity increases upon only slight cooling 
after gelatinization. Viscosities of many of the starch derivatives, best 
observed by Brabender viscosity measurement, increase dramatically to or 
near to peak readings between the temperatures of 95.degree. and 
70.degree. C. during cooling. This behavior differs markedly from the 
underivatized starch bases which rise in viscosity very gradually to reach 
peak readings at considerably lower temperatures (i.e., less than 
50.degree. C.). 
As is generally expected from most substituted starches, gel strengths of 
the reversible gelling starches are somewhat weaker than the underivatized 
starch bases. The gelatinized starches herein are also sensitive to shear. 
If subjected to constant shear conditions during cooling, as encountered 
during Brabender viscosity analysis, the starches herein do not form a 
gel. If the stable starch pastes which result, however, are thereafter 
reheated and subsequently cooled without shear, the starches will indeed 
form gels at high temperatures. 
The gelling starches herein may be thermally or chemically gelatinized. 
Thermal gelatinization is carried out by cooking the starch in water under 
conditions that will not have a degradative effect upon the starch or its 
derivatization. In order to obtain high temperature gelling properties the 
starch dispersions or solutions should have a pH within the range of about 
3 to 8, preferably 4-6. At pHs of 9-10 and 1-2 no hot gels form, nor do 
they form after standing for several hours at room temperature. The gel 
can be reversed by reheating the gel or by adjusting the pH to 13 or 
above. The gel readily reforms on cooling or pH adjustment to less than 
13. 
Chemical gelatinization (also referred to as cold gelatinization) is 
typically carried out at room temperature using aqueous solutions of 
alkalies (e.g., calcium, barium, potassium, sodium, lithium, 
benzyltrimethylammonium, and tetramethylammonium hydroxide), certain salts 
(e.g., sodium salicylate, sodium, ammonium, or potassium thiocyanate, 
sodium and potassium iodide), and organic compounds (e.g., urea). 
Gelatinization takes place when the sorbed chemical exceeds a certain 
critical concentration. The presence of water is not mandatory. However, 
for the purposes herein, it will be present and necessary for the 
formation of the gel. For the purposes herein only alkali is used to 
effect the gelatinization with the relative amounts of water, alkali, and 
starch being adjusted as necessary to provide the necessary high pH and 
resulting gelatinization. The critical concentration level is dependent 
upon both the type of alkali and starch base. The swelling power of the 
reagents, in general, increases with concentration. A further discussion 
of the critical concentration level and examples of that level may be 
found in "Starch: Chemistry and Technology", Vol. I, ed. by R. L. Whistler 
and E. F. Pascall (New York: Academic Pres, 1967) at pages 304-306, as 
well as in "Handbook of WaterSoluble Gums and Resins", ed, by R. L. 
Davidson, Chapter 22: Starch and Its Modifications by M. W. Rutenberg, 
(New York: McGraw Hill Book Co., 1980) at pages 22-17 to 22-18. 
The chemically gelatinized starches form a gel when the pH is lowered. For 
example, where the starch has been gelatinized with alkali at about pH 13, 
the gel forms when the pH is lowered to less than 12. The gel can be 
reversed by raising the pH or by heating the gel at a pH of 3-8. As with 
thermally-gelatinized starches, the gel readily reforms when the pH is 
lowered or the solution is cooled. The acid is added all at once to 
decrease the pH. As discussed previously, shear may interfere with the gel 
formation. 
The following examples will more fully illustrate the practice of this 
invention but they are not intended to limit its scope. In the examples, 
all parts and percentages are given by weight and all temperatures are in 
degrees Celsius unless otherwise noted. The Brabender viscosities of the 
high temperature gelling starches herein were tested by the following 
procedure: 
A total of 17.15-36.02 g. of anhydrous starch is slurried in sufficient 
distilled water to provide a total charge weight of 490 g. The 3.5-7.4% 
anhydrous solids slurries are then poured into the Brabender cup. The 
viscosity is measured using a Visco-Amylo-Graph equipped with a 700 cg 
tension cartridge (manufactured by C. W. Brabender Instruments, Inc., 
Hackensack, New Jersey) as follows: The starch slurry is rapidly heated to 
95.degree. C. and held at that temperature for 15 minutes to effect 
gelatinization. Thereafter, the temperature of the starch dispersion is 
cooled at a rate of approximately 1.5.degree. C. per minute to 55.degree. 
C. For the high amylose starch samples, 17% solids slurries were jet 
cooked prior to employing the above procedure. 
EXAMPLE 1 
This example illustrates the preparation of starch derivatives which are 
high temperature gelling. A series of long linear chain succinate 
derivatives of corn starch were prepared by reacting the starch with 10% 
of various C.sub.10 -C.sub.18 linear alkyl or alkenyl substituted succinic 
anhydrides by the following procedure: 
About 100 parts (as is) of corn starch and 0.7 parts trioctylmethylammonium 
chloride (TOMAC) phase-transfer agent were slurried in about 125 parts of 
tap water, and the pH was adjusted to 8 by the addition of dilute sodium 
hydroxide (3%). A total of 10 parts of alkyl or alkenylsuccinic anhydride 
reagent was added slowly to the agitated starch slurry and the pH was 
maintained at 8 by the metered addition of the dilute sodium hydroxide. 
Agitation was continued for from 5.5-25 hours at ambient temperature. 
After the reaction was complete, the pH was adjusted to about 5.5 with 
dilute hydrochloric acid (3:1). The resultant starch half-esters were 
recovered by filtration, washed three times with water having a pH of 
about 5-6, and air dried. 
An 8 g (as is) portion of each starch derivative was added to 96 g water in 
a glass cup and placed in a boiling water bath (BWB). The starch slurry 
was stirred with a glass stirring rod for about two minutes while the 
starch gelatinized. A rubber stopper was then placed over the rod and cup 
while the starch continued to cook for a total of 20 minutes in order to 
effect complete gelatinization. Each starch was evaluated shortly after 
removal from the BWB and observed for the presence or absence of gel 
formation at high temperatures. A starch was termed to be high temperature 
(HT) gelling if rapid gel formation was observed while the starch cook was 
still hot (i.e., above 70.degree. C.) 
Corn starch was blended with n-octadecyl disodium succinate (which is 
incapable of reacting with a starch molecule) employing the same reaction 
conditions as described above. The gelling properties of this blend of 
starch and long linear chain succinate were compared with those of the 
starch derivatives. 
Table I includes the high temperature gel formation data of the various 
starch half-esters. 
TABLE I 
______________________________________ 
Succinic Anhydride 
Hydrocarbon High Temp. Gel 
Reagent Chain Length Formation 
______________________________________ 
Control (no reagent) 
-- none 
n-Decenyl* 10 none 
n-Dodecenyl* 12 none 
n-Tetradecenyl 14 yes 
n-Octadecyl 18 yes 
n-Octadecenyl 18 yes 
n-Octadecenyl 18 yes 
Sulfosuccinic anhydride** 
n-Octadecyl disodium 
18 none 
succinate (comparative) 
______________________________________ 
*The starch cook formed a very weak gel at room temperature upon standing 
**No phase transfer agent was used for starch derivative preparation. 
The results showed that starch half-esters having a linear hydrocarbon 
chain containing at least 14 carbon atoms possessed high temperature 
gelling properties. 
Brabender evaluation (described above) of the high temperature gelling 
succinate derivatives showed that all possessed dramatic viscosity 
increases compared to corn starch alone during the cooling cycle from 
95.degree. to 70.degree. C. During this portion of the cooling cycle, the 
derivatives (evaluated at 6.9-7.4% solids) all increased in viscosity from 
about 700 to 1150 Brabender units over the increase experienced by the 
corn starch base alone. 
EXAMPLE 2 
This example compares the gel strength of a high temperature gelling corn 
starch derivative with an underivatized corn starch base while at 
70.degree. C. This example also compares the viscosity increase of each 
starch dispersion upon cooling. 
Corn starch was reacted as described in Example 1 with 10% 
tetradecenylsuccinic anhydride in the presence of 1% Aliquat.RTM. 336 
(tricaprylylmethyl ammonium chloride obtained from General Mills 
Chemicals). Seven percent solids (based on dry basis) slurries of the 
derivatized starch (Y) and the underivatized corn starch base (X) were 
prepared. The samples were cooked in a BWB as in Example 1 then cooled to 
and maintained at 70.degree. C. The gel strengths of both samples were 
measured employing a penetrometer (Stevens LFRA Texture Analyzer) after 1, 
2, and 16 hours holding at 70.degree. C. and compared to the gel strengths 
of gelatinized samples which were cooled and maintained at room 
temperature for 16 hours. The gel strengths were measured in grams 
employing probe #6 (a 1 inch diameter cylinder) at a speed setting of 0.5 
for a distance of 0.04 mm. The results may be found in Table II. 
TABLE II 
______________________________________ 
GEL STRENGTH IN GRAMS 
Time at 70.degree. C. 
Corn Starch 
Tetradecenyl Succinate 
(hrs.) Control (X) 
of Corn Starch (Y) 
______________________________________ 
1 26 62 
2 25 82 
16 29 105 
16* 168 108 
______________________________________ 
*Hours at room temperature. 
The results showed that the corn starch derivative had a significant gel 
structure while at 70.degree. C. which increased over time to 
substantially the same gel strength as if it had been cooled to room 
temperature. The corn starch base, however, had no gel structure initially 
at 70.degree. C. nor did it increase to any extent over time at that 
temperature. The room temperature gel strength of the derivative was seen 
to be less than that for the corn starch base. It is believed that 
complexation does decrease the amount of retrogradation somewhat, thus 
weakening the overall gel strength of the derivative. 
Seven percent solids (dry basis) slurries of the tetradecenyl starch 
succinate Y and the corn starch control X were also compared by Brabender 
evaluation by the procedure described above with two minor variations. The 
total charge weight of each starch slurry was 461.7 grams instead of 490 
grams and each starch dispersion was cooled to 27.degree. C. instead of 
55.degree. C. The results, presented in the accompanying drawing, show 
that the viscosity of starch Y increased substantially upon cooling from 
only 95.degree. to 80.degree. C. At 70.degree. C., starch Y had 
approximately reached its peak viscosity. The viscosity of control starch 
X did not begin to increase upon cooling until about 80.degree. C., and 
then proceeded to increase only very gradually upon further cooling. 
EXAMPLE 3 
This example illustrates the preparation of high temperature gelling 
starches employing starch bases other than corn starch. 
Samples were prepared and recovered as described in Example 2. The reaction 
and high temperature gelling property data of the starch samples may be 
found in Table III. 
TABLE III 
______________________________________ 
Succinic 
% Gelatinization Data 
Approx. An- Treat- RT HT 
Starch % hydride ment % Gel Gel 
Base Amylose Reagent Level Solids 
Form. Form. 
______________________________________ 
Waxy 1 -- 0 6 none none 
Maize n-Tetra- 10 6 none none 
(com- decenyl 
parative) n-Octa- 10 6 none none 
decyl 
Rice 17 -- 0 7 yes none 
n-Tetra- 10 7 yes yes 
decenyl 
Tapioca 
18 -- 0 6 none none 
n-Tetra- 10 6 yes yes 
decenyl 
Potato 23 -- 0 8 none none 
n-Tetra- 10 8 yes yes 
decenyl 
Corn .sup. 28.sup.a 
-- 0 7 yes none 
Flour n-Tetra- 10 7 yes yes 
decenyl 
High 70 -- 0 25 yes none 
Amylose n-Tetra- 10 25 yes yes 
Corn.sup.b decenyl 
n-Tetra- 30 25 yes yes 
decenyl 
______________________________________ 
.sup.a Based on starch content of flour. 
.sup.b Samples were fully gelatinized by conventional jetcooking at 
300.degree. F. 
The results showed that other starch bases containing at least about 17% 
amylose may be used to prepare high temperature gelling derivatives. A low 
amylose-content base, such as waxy maize, was seen to not be useful 
herein. 
Brabender evaluation also showed dramatic viscosity increases during the 
initial cooling cycle from 95.degree. to 70.degree. C. for the high 
temperature gelling starch derivatives over their respective bases except 
for the high amylose corn derivatives. Due to the fact that the high 
amylose derivatives were observed in cook evaluations without shear to 
begin gel formation at a higher temperature upon cooling than the other 
starch base derivatives, it was determined that these derivatives are more 
sensitive to the shear conditions of the Brabender evaluation. The waxy 
maize derivative showed no high temperature viscosity increase further 
indicating the necessity for sufficient amylose content in order for 
complexation to occur. 
EXAMPLE 4 
This example illustrates the effect of added sugars on the high temperature 
gelling properties of the starch succinate derivatives herein. 
Aqueous slurries containing 7% solids anhydrous starch (tetradecenyl corn 
starch succinate of Example 2) and 20-30% sucrose or fructose were 
prepared and evaluated for high temperature gel formation and Brabender 
viscosity. The sugars did not inhibit high temperature gel formation or 
weaken the gel strength in comparison to a control sample which contained 
no added sugar. Only the rapid viscosity increase of the derivative in the 
presence of the sugars occurred at a somewhat lower temperature than the 
derivative without sugar (i.e., 75.degree. C. instead of 83.degree. C.). 
EXAMPLE 5 
This example illustrates the effect various salts have on the high 
temperature gelling properties of the starch succinate derivatives herein. 
Aqueous slurries containing 7% solids anhydrous starch (tetradecenyl corn 
starch succinate of Example 2) and 2-5% of either sodium chloride, 
magnesium chloride, calcium chloride, or sodium phosphate were prepared 
and evaluated for high temperature gel formation and Brabender viscosity. 
The results showed that at such treatment levels, sodium chloride and 
magnesium chloride do not inhibit high temperature gel formation. In fact, 
the presence of sodium chloride caused the rapid viscosity increase of the 
derivative to occur at a higher temperature than the derivative without 
sodium chloride (i.e., 89.degree. C. instead of 82.degree. C.) In the 
presence of calcium chloride and sodium phosphate, the succinate 
derivative was neither high temperature gelling or capable of forming a 
gel upon cooling to room temperature. 
EXAMPLE 6 
This example illustrates the thermal reversibility of the high temperature 
gelling starches. 
Aqueous slurries (7% solids) of an underivatized corn starch base and the 
tetradecenyl corn starch succinate of Example 2 were cooked in a BWB for 
20 minutes in order to fully gelatinize the starches and then cooled to 
room temperature for 24 hours. The samples both formed gels. As previously 
noted, the starch succinate was high temperature gelling while the corn 
starch base formed a gel only upon standing at room temperature. 
The starch succinate and starch base gels were recooked in the BWB for 30 
minutes with moderate initial stirring. The starch succinate gel readily 
melted to a flowable dispersion upon reheating having the same consistency 
as it previously had after gelatinization. Conversely, the corn starch gel 
did not readily melt, but rather exhibited a non-flowable, lumpy 
consistency. After removal from the BWB and upon recooling, the starch 
succinate again exhibited high temperature gelling properties. After 
cooling completely to room temperature for 24 hours, the corn starch gel 
was seen to possess a chunky texture while the starch succinate gel had 
the same uniform appearance as it had prior to reheating. 
EXAMPLE 7 
This example illustrates the effect crosslinking has on high temperature 
gelling starch derivatives. 
A. Corn starch crosslinked with 0.003% epichlorohydrin was prepared as 
described in U.S. Pat. No. 2,500,950 (issued Mar. 21, 1950 to M. 
Konigsberg). Portions of the starch were then treated with either 10% 
octadecylsuccinic anhydride or 10% tetradecenylsuccinic anhydride and 
later cooked to observe gelatinization as in Example 1. Both derivatives 
possessed high temperature gelling properties not observed in the 
crosslinked base alone. The C-18 alkyl derivative was noted to have a 
noticeably weaker gel strength than its crosslinked base at room 
temperature as compared to the C-14 alkenyl derivative. 
B. Corn starch was crosslinked with 0.002-0.02% phosphorous oxychloride as 
described in U.S. Pat. No. 2,328,537 (issued Sept. 7, 1943 to G. E. Felton 
et al.). The crosslinked starches were then treated with 10% 
tetradecenylsuccinic anhydride as in Example 1. The derivatives which were 
crosslinked with up to 0.01% of the crosslinking agent were high 
temperature gelling. More highly crosslinked samples (prepared with 
0.015-0.02% crosslinking agent) were not high temperature gelling. 
EXAMPLE 8 
This example illustrates the effect other substituent groups have on high 
temperature gelling starch derivatives. 
A. Hydroxypropylated starch samples were prepared as described below prior 
to being treated with tetradecenylsuccinic anhydride. 
A total of 0.2 to 10 parts propylene oxide (PO) was added to a series of 
reaction vessels which each contained a slurry comprising 100 parts corn 
starch, 125 parts water, 1.5 parts sodium hydroxide and 25 parts sodium 
sulfate. The reaction vessels were sealed then agitated at 40.degree. C. 
for 16 hours. After cooling to room temperature each slurry was adjusted 
to pH of 3 with aqueous 3:1 sulfuric acid then raised to pH 6 prior to 
recovery. The starch samples were recovered by filtration, washed 4 times 
with pH 6 water and air dried. 
All hydroxypropylated starches were treated with 10% tetradecenylsuccinic 
anhydride (TDSA) as described in Example 2 and evaluated for high 
temperature gel formation. The results are shown in Table IV. 
TABLE IV 
______________________________________ 
PO/TDSA 
PO Treatment Treatment 
(%) Cook (7% solids) 
(%) Cook (7% solids) 
______________________________________ 
0.2 not stable 0.2/10 hot gel 
1.0 not stable 1.0/10 hot gel 
2.0 not stable 2.0/10 hot gel 
3.0 stable-cohesive 
3.0/10 hot gel 
3.6 stable-cohesive 
3.6/10 hot gel 
5.0 stable-cohesive 
5.0/10 room temp. gel 
7.5 stable-cohesive 
7.5/10 no gel 
10.0 stable-cohesive 
10.0/10 no gel 
______________________________________ 
*after 2 hours 
The results show that the samples treated with at least 2% propylene oxide 
produced stable starch cooks while those starches treated with less 
propylene oxide were not stable after cooling to room temperature. The 
results show that the dual-treated starches (i.e., PO and TDSA) were high 
temperature gelling when the starch was treated with &lt;5% propylene oxide, 
corresponding to a theoretical degree of substitution (D.S.) of &lt;0.144. At 
higher propylene oxide substitution levels (D.S. of 0.144), the 
dual-treated starches formed room temperature gels which were reversible. 
At even higher PO substitution levels (D.S. &gt;0.144 up to 0.275), the 
dual-treated starches formed no gel. 
The dual-treated samples produced weaker gels and appeared somewhat more 
shear sensitive than a starch sample treated only with the 
tetradecenylsuccinic anhydride reagent. Most significant was the effect 
provided by the treatment with the long chain reagent which reversed the 
stabilization due to moderate hydroxypropylation. 
B. Cationic starch ethers described in U.S. Pat. No. 2,876,217 (cited 
previously) were prepared as described below prior to being treated with 
tetradecenyl succinic anhydride. 
To a series of starch slurries comprising 100 parts corn starch and 125 
parts water were added 0.5-2.1 parts calcium hydroxide (to maintain a 
reaction pH of at least 12) followed by 0.4 to 6.0 parts of a 50% aqueous 
solution of diethylaminoethylchloride hydrochloride (DEC). The reactions 
were conducted at room temperature for 18 hours. A 3:1 aqueous 
hydrochloric acid solution was added to adjust the pH to 3.0. Thereafter 
the starches were recovered by filtration, washed 4 times with pH 3 water 
and air dried. The cationic starches treated with at least 1% DEC which 
contained 0.14% nitrogen (dry basis) produced stable starch cooks while 
the starches treated with less DEC produced gels, though weaker than that 
of the corn base, after cooling to room temperature. All the cationic 
starches were further treated with 10% tetradecenylsuccinic anhydride as 
described in Example 1 and evaluated for high temperature gel formation. 
All the dual-treated samples were high temperature gelling, possessing 
stronger gel structures than the above dual-treated hydroxypropylated 
samples. Upon cooking, the samples also foamed. The stronger gel formation 
may be attributed to the ionic interaction between the cationic and 
anionic substituents. 
EXAMPLE 9 
This example illustrates the use of other reagents which provide starch 
derivatives that possess high temperature gelling properties. Corn starch 
was treated with the reaction products of N-methylimidazole with C.sub.10 
-C.sub.16 alkyl carboxylic acid chlorides, benzoyl chloride and 
cyclohexanoyl chloride. 
Starch was reacted with the reagents employing a procedure described in 
U.S. Pat. No. 4,020,272 (cited previously). The procedure comprised 
slurrying 100 parts corn starch (as is) in 150 parts water at pH 8 and 
then slowly adding the reagent to the slurry. The reaction was conducted 
for 2 to 3 hours at room temperature while maintaining the pH at 8 as 
described in Example 1. When the reaction was complete, the pH of the 
slurry was adjusted to 4 with 3:1 hydrochloric acid. The starch ester 
derivatives were recovered by filtration, washed three times with water 
having a pH of about 4, and air dried. The reaction data as well as the 
high temperature gelling properties of 7% solids slurries may be found in 
Table V. 
TABLE V 
______________________________________ 
Reagent 
N--methylimidazolium 
% Treatment 
High Temp. 
chloride of Level Gel Formation 
______________________________________ 
Benzoic acid 5 none 
10 none 
Cyclohexanoic 5 none 
10 none 
Capric acid (C.sub.10)* 
5 none 
10 none 
Lauric acid (C.sub.12) 
5 yes 
Myristic acid (C.sub.14) 
5 yes 
Palmitic acid (C.sub.16) 
5 yes 
______________________________________ 
*The starch cook was stable at room temperature. 
The results showed that only starch ester derivatives having a long 
hydrocarbon chain substituent comprising at least 12 carbon atoms produced 
high temperature gels. The cycloalkyl and aryl substituents, e.g., of 
cyclohexane and benzene did not produce high temperature gelling starches. 
Brabender evaluation of the C.sub.12 -C.sub.16 high temperature gelling 
derivatives at 7.35% anhydrous solids and 5.5 pH showed that all exhibited 
rapid viscosity increases during the cooling cycle. From 95.degree. to 
70.degree. C., the derivatives each increased in viscosity by about 1,100 
Brabender units over the increase experienced by the corn starch base 
alone. 
EXAMPLE 10 
High temperature gelling starch ethers were prepared employing long chain 
quaternary amine epoxide reagents. The reagents employed comprised the 
reaction products of epichlorohydrin with C.sub.10 -C.sub.16 alkyl 
dimethyl amines. 
Starch was reacted with the reagents employing the procedure described in 
U.S. Pat. No. 2,876,217 (cited previously). The procedure comprised 
slurrying 100 parts starch (as is) in 125 to 150 parts water containing 10 
parts sodium sulfate and 2 parts sodium hydroxide. A total of 5-10 parts 
reagent was added. The mixture was agitated for 16 hours at 40.degree. C. 
and then the pH was adjusted to 3 with 3:1 hydrochloric acid. The starch 
ethers were filtered (methanol was added to aid in the filtration), then 
washed three times with water having a pH of about 3, and air dried. The 
reaction and high temperature gelling data may be found in Table VI. 
TABLE VI 
______________________________________ 
N,N--dimethyl-N--gly- 
cidyl-N--alkyl ammonium 
chloride Reagent % Nitrogen 
Starch Alkyl Carbon 
Treatment on starch 
High Temp. 
Base Length Level (%) (d.b.) Gel Form. 
______________________________________ 
Corn 10* 10 0.20 none 
12* 10 0.19 none 
14 6 0.10 yes 
16 5 0.15 yes 
16 10 0.23 yes 
Tapioca 
16 5 0.10 yes 
10 0.18 yes 
Potato 16 5 0.08 yes 
10 0.20 yes 
______________________________________ 
*The starch cook formed a very weak gel at room temperature upon standing 
 
The results showed that only the starch ether derivatives having long 
hydrocarbon chain substituents comprising at least 14 carbon atoms 
produced high temperature gels. 
Although not as dramatic as the starch succinates and full ester 
derivatives described above, Brabender evaluation of the corn based starch 
ethers herein at 7% anhydrous solids showed the derivatives to exhibit 
signficant increases in viscosity over the corn base (.about.200 Brabender 
units) above 70.degree. C. while cooling. 
EXAMPLE 11 
This example illustrates the effect hydrolysis has on high temperature 
gelling starch derivatives. 
Samples of corn starch were hydrolyzed with hydrochloric acid to water 
fluidities (WF's) of 9, 20, 25, and 40. Potato and tapioca starches were 
similarly hydrolyzed. The hydrolyzed samples were reacted with 10% 
tetradecenylsuccinic anhydride in the presence of 1.0% Aliquat.RTM. 336 
for 24 hours at room temperature, recovered as described in Example 1, and 
compared with the unhydrolyzed starch succinates of Example 3. 
Aqueous 8 to 15% solids (as is) slurries of the starches were cooked as in 
Example 1 then evaluated for high temperature gelling properties. Of the 
fluidity corn starches, only those derivatives prepared from fluidities of 
25 or less produced high temperature gels. As the degree of hydrolysis was 
increased, it was noted the resultant starch succinates provided weaker 
high temperature gels compared to the non-hydrolyzed derivative. The 40 WF 
sample did not gel, but remained stable during cooling and at room 
temperature. 
None of the derivatized potato or tapioca fluidities were high temperature 
gelling. 
Hydrolyzed corn starches having water fluidities of approximately 20 to 60 
were also reacted with 10% of the C.sub.14 quaternary amine epoxide 
reagent of Example 10 and compared at similar solids levels to the 
nonhydrolyzed derivative. All samples produced high temperature gels. 
However, as the degree of hydrolysis increased, it was again noted the 
high temperature gels became increasingly weaker. 
The results indicate that some converted bases may be employed in the 
preparation of high temperature gelling starches. The particular starch 
base and the long chain derivatization were seen to influence the maximum 
degree of hydrolysis of a starch which will still produce an acceptable 
high temperature gel. 
EXAMPLE 12 
This example determines the pH at which the high temperature gelling 
starches hot gel. 
Samples (6 g. each) of the corn starch half-ester formed by treatment with 
10% tetradecenyl succinic anhydride were slurried in 94 g. of water. They 
were adjusted to pH values ranging from 1 through 10 by the addition of 
aqueous sodium hydroxide or hydrochloric acid as required. They were then 
cooked for 15 minutes in a boiling water bath. The cooks prepared at pH 1 
and 2 were water thin due to acid hydrolysis. No gels were formed after 
cooling for several hours at room temperature. The cooks prepared at pH 
3-8 formed hot gels. Those prepared at pH 9 and 10 did not form hot gels, 
nor did they form gels after cooling. The gels were thermally reversible, 
carried out by reheating and cooling at a pH of 3-8. They were also 
chemically reversible, carried out by adjusting the pH to 13 or above as 
shown in the next Example. 
EXAMPLE 13 
This example demonstrates that chemically gelatinized starches form 
reversible gels. 
Samples (7.5 g. each) of the corn starch half-ester formed by treatment 
with 10% tetradecenyl succinic anhydride were slurried in 95 ml. of water 
and 5 ml. of 20% sodium hydroxide was added. The slurry (about pH 13) was 
stirred vigorously and after a few minutes the starch was fully 
gelatinized. Enough aqueous hydrochloric acid was added all at once to 
decrease the pH to 10.0, 6.0, 3.5, and 1.0. All of the starches showed gel 
formation upon lowering the pH. The gel was reversed by raising the pH of 
the gel to above 13 and reformed again on lowering the pH. The gel formed 
at pH 6 was also thermally reversible. The gels should be thermally 
reversible within the same pH range as the thermally-gelatinized starches, 
i.e., 3-8. 
EXAMPLE 14 
This example illustrates the preparation of starch half-acid esters by 
reacting corn starch with four different hydrophobic substituted succinic 
anhydrides under aqueous conditions in the presence of various phase 
transfer agents. 
About 100 parts (as is) of granular corn starch and 0.7 parts phase 
transfer agent were slurried in about 125 to 150 parts of tap water, and 
the pH was adjusted to 8 by the addition of dilute sodium hydroxide. A 
total of 10 parts of a C.sub.8 -C.sub.18 hydrophobic substituted succinic 
anhydride was added slowly to the agitated starch slurry, and the pH was 
maintained at 8 by the metered addition of the dilute sodium hydroxide. 
Agitation was continued for 18 to 20 hours at ambient temperature. After 
the reaction was complete, the pH was adjusted to about 5.5 with dilute 
hydrochloric acid (3:1). The resultant starch half-acid esters were 
recovered by filtration, washed three times with water having a pH of 
about 5-6, and air-dried. 
The samples prepared may be found in Table VII. Similar starch reactions 
with the four succinic anhydride reagents were also conducted in the 
absence of any phase transfer agent in order to observe and compare the 
starch products after filtration and, in some samples, to compare the 
carboxyl content of the starches after cooking. The latter gives one an 
indication of the degree of substitution of similar starch reaction 
products. 
TABLE VII 
______________________________________ 
Succinic Anhydride 
Sample 
Substituent Phase Transfer Agent 
______________________________________ 
Quaternary salt; 
A** n-octenyl tricaprylylmethyl ammonium 
chloride* (C.sub.25-31) 
B n-tetradecenyl benzyltriethyl ammonium 
chloride (C.sub.12) 
C n-tetradecenyl tetra-n-butyl ammonium 
chloride (C.sub.16) 
D n-tetradecenyl n-hexadecyltrimethyl ammonium 
bromide (C.sub.19) 
E n-tetradecenyl n-hexadecyl pyridinium 
bromide (C.sub.21) 
F n-tetradecenyl tricaprylylmethyl ammonium 
chloride* (C.sub.25-31) 
G n-tetradecenyl n-hexadecyl-tri-n-butyl 
phosphonium bromide (C.sub.28) 
H n-tetradecenyl tetra-n-octyl ammonium 
bromide (C.sub.32) 
I n-octadecenyl tricaprylylmethyl ammonium 
chloride* (C.sub.25-31) 
J** branched octadecenyl 
tetraethyl ammonium chloride 
monohydrate (C.sub.8) 
K branched octadecenyl 
trioctylmethyl ammonium 
chloride (C.sub.25) 
L branched octadecenyl 
tricaprylylmethyl ammonium 
chloride* (C.sub.25-31) 
Tertiary amine: 
M n-tetradecenyl octyldimethylamine (C.sub.10) 
N n-tetradecenyl didecylmethyl amine (C.sub.21) 
______________________________________ 
*Aliquat .RTM. 336 was employed having a mixture of C.sub.8 -C.sub.10 
hydrocarbon radicals. 
**Comparative 
The quaternary salts used in the preparation of starch samples A-I and L 
provided starch products after filtration in which little, if any, 
unreacted reagent remained on the starch filter cake in comparison to the 
control samples where significant unreacted reagent layers were present. 
Similar benefits were noted with the tertiary amine phase transfer agents. 
Starch Sample A (Comparative) which employed the less hydrophobic 
octenylsuccinic anhydride, had a carboxyl content of 2.42% while a control 
sample prepared without the phase transfer agent had a carboxyl content of 
5.35%. The results indicate that the phase transfer agent, in this case, 
facilitated reagent hydrolysis instead of improving the starch reaction. 
Starch samples J (Comparative) and K were cooked at 7% starch solids in 
water and compared with the same starch product (O) prepared in the 
absence of a phase transfer agent. Samples J and O gave gels similar to 
that of unreacted corn starch. Sample K, however, did not form a gel upon 
cooling but exhibited a cohesive, fluid texture. The results show that a 
quaternary salt having a total of only 8 carbon atoms attached to the 
cation is not useful in the process herein. 
Summarizing, the present invention provides modified starches having unique 
gelling properties which are prepared by chemically reacting an amylose 
containing starch base with an etherification or esterification reagent 
which will introduce a long linear hydrocarbon chain substituent therein. 
The aqueous gels formed by the starches are thermally and pH reversible 
and the thermally-reversible gels are hot gels. 
The present invention provides an improved process for preparing starch 
half-acid esters in water by reacting starch under alkaline conditions 
with a hydrophobic-substituted cyclic dicarboxylic acid anhydride in the 
presence of a phase transfer agent.