Foodstuffs containing crosslinked starches using STMP

The invention discloses a dual derivatizing process for the preparation of cold water swelling starches and foodstuffs thickened therewith. The starch base is first subjected to a primary crosslinking reaction using sodium trimetaphosphate (STMP) according to conventional techniques, then reslurried, treated with additional STMP and drum dried to effect a secondary cross-linking reaction in situ.

BACKGROUND OF THE INVENTION 
I. Field of the Invention 
This invention relates to starches which are crosslinked with sodium 
trimetaphosphate and to foodstuffs thickened therewith. More particularly 
it provides a dual derivatizing process which unexpectedly leads to 
crosslinked starches which provide superior viscosity characteristics when 
used as thickeners as compared to crosslinked starches of the prior art. 
II. Brief Description of the Prior Art 
Recent attempts to replace certain starch derivatives used in foods, e.g., 
epichlorohydrin inhibited starches, with other FDA acceptable starch 
derivatives, have placed new emphasis on starch derivatives formed with 
phosphate derivatizing reagents, especially sodium trimetaphosphate. 
Methods for the production of starch phosphate esters have long been known. 
Thus U.S. Pat. Nos. 2,884,413, 2,801,242, 2,852,393 and 3,021,222, among 
others are directed to processes for the production of such starch 
derivatives and the various uses thereof. These derivatives, when 
contrasted with the corresponding raw, unmodified starches, will differ in 
properties depending upon the base starch employed. In the case of corn 
starch, the crosslinked starch gelatinizes somewhat earlier than the raw 
starch, reaches a higher peak or maximum viscosity and breaks down to a 
lesser extent than the raw starch. In the case of crosslinked amioca 
starch there is also less breakdown than the raw amioca with the 
crosslinked starch products maintaining their maximum viscosity under 
prolonged agitation, elevated temperature and low pH. Additionally, there 
is an improvement in the textural properties of the crosslinked starches 
when contrasted with the unmodified starch. Despite these advantages over 
the unmodified starches, when the crosslinked starches are re-slurried, 
drum dried and ground to a fine powder to make a starch useful in cold 
water swelling applications, serious deficiencies can be noted. Thus after 
the viscosity peak is achieved and maintained for a period of time in the 
initial dispersion, there is a loss of viscosity or "breakdown" in many 
food systems after subsequent cooking or baking. This breakdown results in 
a loss of both useable thickening power and textural properties, with a 
high breakdown usually indicating a gummy, cohesive texture and reversion 
of the starch to its original unmodified characteristics. Another such 
disadvantage is evidenced in thinning of starch stabilized fruit pastes in 
certain bakery products such as fruit filled tarts. This thinning often 
results in a "boil-out" or puncture of the pastry shell during baking 
thereby detracting from the appearance of the tart. 
SUMMARY OF THE INVENTION 
It has now been found that when starch is treated with sodium 
trimetaphosphate (STMP) in accordance with the dual derivatizing process 
of the present invention, and used as a thickener for foodstuffs, the cold 
water swelling crosslinked starch will, depending on the base starch 
employed, provide superior viscosity and textural characteristics. 
According to the process of the present invention the granular starch base 
is derivatized in a primary crosslinking step with STMP at a pH of 10-12 
and at a temperature sufficiently low to maintain the starch in an 
unswollen granular form. The slurry is then neutralized to a pH of 5-6.5, 
recovered and preferably washed in accordance with conventional known 
techniques. At this stage, however, rather than reslurrying and drum 
drying as is carried out in typical STMP reaction procedures of the prior 
art, the starch is reslurried, adjusted to a pH of at least about 7.5 and 
additional STMP is added to the slurry. The resulting slurry is then fed 
onto a drum dryer and drum dried in accordance with conventional 
procedures to effect a secondary crosslinking reaction in situ. 
The foodstuffs thickened with the starches resulting from this unique dual 
derivatizing reaction are characterized by superior viscosity-related 
properties as evidenced by their viscosity curves which, after peaking, 
maintain a high viscosity with little or no degradation or breakdown even 
after exposure to elevated temperatures for extended periods of time. 
While not wishing to be bound by theory, it is thought that this procedure 
is superior to conventional STMP crosslinking techniques in that the 
primary crosslinking reaction occurs only in the outer portions of the 
starch granule with limited penetration, while the subsequent secondary 
crosslinking is effected on a starch product which loses much of its 
granular form during the drum drying step so that the latter crosslinking 
reaction which occurs simultaneously during the drying takes place mainly 
on the dispersed starch and not on the granule.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The applicable starch bases which may be used in the procedure of the 
present invention include any granular starch in raw or modified form. 
Useful starch bases include corn, waxy maize, grain, sorghum, wheat, rice, 
potato, sago, tapioca, sweet potato, high amylose corn, or the like. Also 
included are the conversion products derived from any of the starch bases 
including, for example, dextrins prepared by the hydrolytic action of acid 
and/or heat, oxidized starches prepared by treatment with oxidants such as 
sodium hypochlorite, and fluidity or thin boiling starches prepared by 
enzyme conversion or by mild acid hydrolysis. Particularly preferred 
starches, due to their end use applications, are corn, waxy maize and 
tapioca. 
The primary crosslinking reaction of the starch base with the sodium 
trimetaphosphate reagent may be carried out using any of the procedures 
described in the aforementioned patents, the disclosures of which are 
incorporated herein by reference. Thus, in accordance with a preferred 
procedure, the pH of the aqueous starch slurry is adjusted to a range of 
10 to 12, preferably 11 to 11.5, with any common alkali as, for example, 
with sodium hydroxide. The amount of reagent required to produce minimal 
crosslinking is quite small, i.e., of the order of about 0.03 percent 
based on the dry weight of the starch, when the time of the reaction is 
one hour, the temperature 50.degree. C. and the pH 11. If temperatures 
below 50.degree. C. are used, correspondingly more reagent should be used 
if time and pH are the same. In general, a range of reagent between about 
0.01 and about 0.6 percent will be operable depending on the specific 
reaction conditions. A preferred range is between about 0.03 and about 0.2 
percent. Although amounts higher than 0.6 percent are not detrimental for 
these conditions, such amounts serve no useful purpose. The reaction 
proceeds at a faster rate employing higher temperatures and pH and with 
increased amount of reagent. 
As is known in the art, the addition of sodium ion has a positive effect on 
the degree of phosphorylation with a total sodium ion concentration of 
about 0.4 mole per liter of slurry usually giving satisfactory results 
herein. The optionally added sodium ion is most conveniently provided by 
the addition of sodium chloride to the starch slurry. 
After the additional sodium ions are added, if employed, and the pH of the 
starch slurry has been adjusted to within the required range, the 
crosslinking reaction is allowed to proceed to the desired degree. The 
reaction may be facilitated by heating the slurry with agitation while 
keeping the temperature sufficiently low so as to maintain the starch in 
the unswollen granular state. In general, temperatures between about 
30.degree. and 50.degree. C. are preferred but higher or lower 
temperatures may be used if process conditions are adjusted accordingly. 
When the desired degree of crosslinking has been obtained (usually within 
2-6 hours) as evidenced by monitoring the Brabender curve pattern, the 
crosslinked granular starch is neutralized to a pH range of 5.0-6.5, 
preferably 5 to 5.5, and recovered, as by filtration. 
In accordance with the novel aspects of the present invention, the 
neutralized, primary crosslinked starch is preferably washed and then is 
reslurried in water at a solids concentration of at least about 20%, 
preferably about 38-42%, and sodium ions are optionally added, as by the 
addition of sodium chloride. The pH is then adjusted to at least 7.5, 
preferably 7.8-8.1 as, for example, with sodium carbonate. It will be 
recognized that use of higher pH's will result in higher degrees of the 
secondary crosslinking, however, due to the desired end-use of the 
cross-linked starches in food systems, lower pH conditions (below about 
8.5) are desired since their presence will not detract from the long term 
stability of the food system. Temperatures in the reslurry stage should 
preferably be maintained at less than about 25.degree. C. so as to ensure 
that further primary crosslinking does not occur on the granular starch 
prior to introduction onto the drum dryer. Higher temperatures may be used 
if additional STMP is employed to ensure that sufficient STMP is present 
for the secondary reaction effected on the drum dryer, however, no 
advantage is obtained therewith. Sodium trimetaphosphate is then added to 
the slurry in amounts comparable to those used in the primary crosslinking 
step (i.e., in the order of about 0.01-0.6%, preferably 0.03-0.2%, based 
on the dry weight of the starch). 
The resulting mixture is then fed directly onto a drum dryer and dried to a 
suitable moisture level, usually below about 10%, preferably to about 5%, 
using conventional procedures. The drum dryer may be of an atmospheric 
type and may constitute either a single or double drum. In accordance with 
a preferred embodiment of the invention, the slurry is fed onto a main 
drum with multi-feed applicator rolls through perforated pipes or 
oscillating arms from a tank or vat provided with an agitator. Generally, 
the drum or drums are steam heated to a temperature within the range of 
about 135.degree.-175.degree. C. with the capacity of the drum dryer being 
proportional to the effective drying area, i.e., the total surface from 
which drying can take place. Thus, the aqueous slurry is fed into the nips 
formed by the main heated drum and applicator rolls wherein it gelatinizes 
and forms a rolling cylinder of starch paste thereby effecting secondary 
crosslinking with the reagent while also evaporating the water therefrom 
so as to ultimately yield dry, solid particles of pregelatinized dually 
crosslinked starch. It will be recognized that the drum drying conditions, 
e.g., temperature and drum speeds, under which the starch is gelatinized, 
crosslinked and dried in this secondary reaction step will vary according 
to the particular starch base, the degree of crosslinking desired and the 
ultimate end-use application. 
After drying, the dried sheet is removed, as by doctoring from the drum, 
and flaked, ground or milled to the desired mesh depending upon the 
end-use requirements employing procedures and apparatus well known to 
those skilled in the art. 
In the following examples, which further illustrate the embodiments of the 
invention, all parts are by weight and all temperatures in degrees Celsius 
unless otherwise noted. In the examples, the properties of the starches 
are characterized by their respective Brabender curve patterns as 
illustrated in the Figures presented herein. The Brabender viscometer is 
used to give a continuous viscosity reading of a sample which is agitated 
as the temperature is increased at a uniform rate. Thus, aqueous 
suspensions of the starch are heated to temperatures above the 
gelatinization point, then held at that temperature for selected periods 
of time. The instrument thereby generates a complete history of cooking 
and swelling showing the onset of gelatinization, the peak or maximum 
viscosity reached, the slope of the curve traced in reaching the peak and 
the change in viscosity, if any, after reaching the peak. 
EXAMPLE 1 
This example illustrates the production of a crosslinked cold water 
swelling amioca starch in accordance with the present invention. 
A water slurry of amioca at about 36% solids and 35.degree.-38.degree. C. 
was treated with 0.6% sodium chloride (based on starch solids). A water 
solution containing 3% by weight of sodium hydroxide was added until the 
total amount of sodium hydroxide was 0.6% of the weight of the starch. The 
pH at this stage was in the range 11.1-11.4. To this system, 0.18% sodium 
trimetaphosphate was added and allowed to react for about 3 hours. After 
the reaction, the system was neutralized to a pH range of 5.0-5.5 with 
hydrochloric acid and the starch was recovered by filtration. The starch 
was then washed and dried to a powder containing about 12% moisture. 
A portion of the resultant starch was reslurried in water, drum dried and 
milled according to prior art pregelatinization techniques and was set 
aside as a control. 
The remainder of the crosslinked amioca was then reslurried in water at a 
solids concentration of 38-42%. To this slurry was added 0.5% sodium 
chloride and 0.15% sodium trimetaphosphate based on the weight of the 
starch. The pH of the slurry was then adjusted to a range of 7.8-8.1 with 
sodium carbonate and drum dried with steam at about 100 psig pressure. The 
dried sheet was removed from the drum surface and milled to a powder such 
that 85-90% by weight would pass through a 200 mesh U.S. standard sieve. 
A viscosity curve obtained by Brabender analyses of the resulting dually 
crosslinked starch is shown in FIG. 1 and compared with the curve obtained 
from the control distarch phosphate ester prepared above in accordance 
with prior art techniques. The Brabender testing was performed on a 
simulated fruit pie filling mixture prepared by blending starch with sugar 
and water to produce a dispersion containing 4.6% starch solids and 23% 
sugar and adjusting the pH to 2.7 with acetic acid. The mixture was then 
pre-mixed for 3 minutes, held at 30.degree. C. for 10 minutes, heated to 
95.degree. C. and held at 95.degree. C. for an additional 10 minutes as 
indicated in the figure. 
In Curve A (the control), the viscosity peak is achieved within 10-15 min. 
after starting the heating cycle at a temperature of about 50.degree. C. 
Thereafter, with continuous heating until a temperature of about 
95.degree. C. is reached and maintained, there is an undesirable loss of 
viscosity or breakdown. In contrast, the improved properties obtained with 
the starch prepared using the novel dual crosslinking process of the 
present invention are shown in Curve B. Here, the viscosity developed 
during the first 10 minutes, when the temperature is maintained at 
30.degree. C., is the result of pregelatinization/cold water swelling. 
After the start of heating, and during a uniform increase in temperature 
from 30.degree. C. to 95.degree. C., the viscosity has peaked and 
stabilized, in fact increasing slightly from the start to the end of the 
heating cycle. In addition to this significant resistance to viscosity 
breakdown, other disadvantages of the prior art materials are also 
practically eliminated. There is little or no loss in viscosity during 
heating, thus retaining thickening power, the texture is "short" without 
any tendency towards gumminess, and when used in fruit filling for tarts, 
the puncturing of the pastry shells is sharply reduced. 
EXAMPLE 2 
This example illustrates the production of a crosslinked cold water 
swelling corn starch in accordance with the method of the present 
invention. The resultant starch is characterized by a high viscosity curve 
and will produce a grainy or "pulpy" textured paste. 
A water slurry of unmodified corn starch at about 36% solids and 
35.degree.-38.degree. C. was treated with 1.15% sodium chloride based on 
the weight of starch solids. A water solution containing 3% by weight 
sodium hydroxide was added until the total amount of sodium hydroxide was 
0.6% of the weight of the starch. The pH was then in the range of 
11.1-11.3. Sodium trimetaphosphate in an amount of 0.15% based on the 
weight of the starch was added and allowed to react for about 3 hours. 
After reaction, the batch was neutralized to the pH range of 5.0-5.5 with 
hydrochloric acid. The starch was then recovered, washed and dried to a 
powder containing about 12% moisture. 
As a control, a portion of the crosslinked starch was re-slurried and drum 
dried using conventional techniques to produce a cold water swellable 
starch. 
The remainder of the crosslinked starch was re-slurried in water to an 
anhydrous solids concentration of 38-42% and then 0.5% sodium chloride and 
0.2% sodium trimetaphosphate was added thereto. The pH of the slurry was 
adjusted to the range of 7.8-8.1 with sodium carbonate, and the starch 
slurry was drum dried using steam at about 100 psig pressure. The dried 
sheet was removed from the drum surface and milled to a coarse flake such 
that no more than 28% by weight will pass through a 100 mesh U.S. standard 
sieve. 
A Brabender curve for the resultant dually crosslinked starch is shown in 
FIG. 2 as Curve B and compared with the control (Curve A prepared as 
described above). The Brabender test performed in this example was done on 
a dispersion containing starch at 7.6% solids with acetic acid added to 
adjust the pH to 2.9. The maximum viscosity developed by the products 
prepared in accordance with the present invention is significantly higher 
than that achieved with the control starch. Even more dramatic than the 
change in viscosity pattern is the performance of the dually inhibited 
cold water swelling starches in retorted pastes and sauces, particularly 
those made with tomato. The heavy-bodied, "pulpy" or grainy texture which 
develops and is sustained on extended retorting in both high and low pH 
systems is more pronounced than in the systems of other products made with 
a single, granular inhibited base (including those inhibited with reagents 
other than sodium trimetaphosphate). This improvement in properties is 
most desirable in a product such as tomato sauce for spaghetti where a 
thick naturally "pulpy" texture and "mouth feel" are particularly 
important. 
While it might be considered that the textural properties of the control 
starch (shown in Curve A, FIG. 2) would be improved without the necessity 
for the dual crosslinking merely by increasing the level of the primary 
crosslinking, such improvements have not, in practice, been observed. 
Thus, when the primary reaction is continued for a longer period of time 
using additional reagent, a Brabender curve pattern represented by that 
shown in Curve C, FIG. 2 is produced. Thus, such excessive crosslinking 
results only in a starch which is so highly crosslinked that it will not 
adequately cook and will produce opaque, low viscosity properties when 
used in foodstuffs. 
EXAMPLE 3 
This example illustrates the production of a crosslinked cold water 
swelling tapioca starch prepared in accordance with the method of the 
present invention. The dually inhibited starch is characterized by being 
readily dispersible in cold systems wherein it provides high viscosity and 
a "pulpy" textural appearance. 
An aqueous slurry of tapioca starch at about 36% solids and 
35.degree.-38.degree. C. was treated with 1.15% sodium chloride, based on 
the weight of the starch solids. A water solution containing 3% by weight 
of sodium hydroxide was added until the total sodium hydroxide was 0.6% of 
the weight of the starch. Sodium trimetaphosphate in an amount of 0.06% by 
weight was then added and allowed to react for 3 to 5 hours. After the 
reaction, the slurry was neutralized to a pH range of 5.0-5.5 with 
hydrochloric acid, washed and dried. 
A portion of the resultant crosslinked starch was reslurried and drum dried 
to provide a control starch, pregelatinized in accordance with prior art 
techniques. 
The remaining crosslinked starch was re-slurried in water to an anhydrous 
concentration of about 40% and thereafter 0.5% by weight sodium chloride 
and 0.15% sodium trimetaphosphate was added. The pH was adjusted to the 
range of 7.8-8.1 with sodium carbonate. The slurry was then drum dried 
with steam at 100 psig pressure, doctored from the drum and milled to a 
coarse powder so that a maximum of 30% by weight would pass through a 100 
mesh U.S. standard sieve. 
Brabender tests were performed as described in Example 1 with Brabender 
viscosity curves for the control starch (Curve A) and the dually inhibited 
starch of the present invention (Curve B) shown in FIG. 3. It is clearly 
seen that the curve of the control starch reaches a high, early peak 
viscosity, then shows a steep, rapid rate of breakdown. In contrast, the 
curve of the product made in accordance with the present invention shows a 
restricted rise in viscosity, sustained high viscosity over an extended 
time followed by breakdown to a higher final viscosity. Additionally, when 
used in cold water dispersion at neutral or acid pH ranges, the starches 
produced in accordance with the present invention are much heavier bodied, 
giving a "pulpier" texture than the control starch. 
EXAMPLE 4 (Comparative) 
In order to ascertain whether both inhibition steps are required or if the 
unique properties achieved by the process of the present invention could 
be obtained by performing only the secondary "in-situ" crosslinking step 
on the drum drier, the following example was performed. The Brabender 
tests were performed using the procedure described in Example 1. 
Amioca starch (such as was used in Example 1) was slurried in water at an 
anhydrous solids concentration of 36% and treated with 0.5% sodium 
chloride and 0.25% sodium trimetaphosphate. After adjusting the pH to 
7.8-8.1 with sodium carbonate, the batch was drum dried with steam at 100 
psig pressure, then milled so that 85-90% passed through a 200 mesh U.S. 
standard sieve. The Brabender curve for this starch product is shown in 
FIG. 4, Curve B. 
A second crosslinked starch was prepared as above except that the amount of 
sodium trimetaphosphate was increased to 0.40% by weight of the starch. 
This product is represented by Curve C. 
As a control, raw amioca starch was pregelatinized according to 
conventional techniques. Thus, the amioca was treated as above, but no 
sodium trimetaphosphate was employed. This control starch is represented 
by Curve A. 
A comparison of the three starches shows that the raw amioca, 
pregelatinized by drum drying (Curve A) is characterized by very early 
peak viscosity (the maximum being reached during the 3 minutes pre-mixing) 
high breakdown and a very gummy cohesive texture. The viscosity pattern 
for the crosslinked starches (Curves B and C) is unexpected in view of the 
results obtained using the process of the present invention as illustrated 
in Examples 1-3. Thus, maximum viscosities are reached early, (during the 
3 minute pre-mixing) and the breakdowns are also very high. Additionally, 
gummy, cohesive textures are even more pronounced than observed for the 
control. Moreover, the maximum viscosity for the starch prepared with 
0.25% sodium trimetaphosphate was 1.5 times that of the control and for 
the starch prepared with 0.40% sodium trimetaphosphate, it was almost 2.5 
times the control. 
The preferred embodiments of the present invention having been described 
above, various modifications and improvements thereon will now become 
readily apparent to those skilled in the art. Accordingly, the spirit and 
scope of the present invention is defined not by the foregoing disclosure, 
but only by the appended claims.