Novel Starch and Products Produced Therefrom

This invention relates to starch and more particularly to starch which has been extracted from a plant having an amylose extender dull shrunken-1 (aedush1) homozygous genotype.

Starch occurs in a variety of plants and is generally categorized based on its plant source. For example, cereal starches are extracted from cereal grains such as maize, rice, wheat, barley, oats and sorghum; tuber and root starches are extracted from plants such as potato, sweet potato, arrowroot, yams and cassava; and waxy starches are extracted from plants such as waxy maize, waxy rice, waxy barley and waxy sorghum.

Generally, starch is comprised of two polymers, amylose and amylopectin which are intertwined to form a starch granule. Amylose is a linear polymer of alpha 1-4 bonded anhydroglucose units while amylopectin is a branched polymer comprised of linear chains of alpha 1-4 linked anhydroglucose units with branches resulting from alpha 1-6 linkages between the linear chains.

Each starch bearing plant produces different percentages of amylose and amylopectin, different size granules and different polymeric weights for both the amylose and amylopectin. These differences produce markedly different properties in the starch.

Heretofore, the only way to affect the properties of starch was to physically and/or chemically treat the starch.

It has recently been discovered that there exists a number of recessive mutant genes in starch bearing plants which have an affect on the properties of starch and that by controlled breeding these mutant genes can be expressed.

Some of the mutant genes which have been identified in maize include the genotypes: waxy (wx), amylose extender (ae), dull (du), horny (h), shrunken (sh), brittle (bt), floury (fl), opaque (o), and sugary (su). Nomenclature for some of these mutant genes is based in part on the effect these mutant genes have on the physical appearance, phenotype, of the kernel. It is also known that within these genotypes there are genes which produce starches with markedly different functional properties even though the phenotypes are the same. Such subspecies have generally been given a number after the named genotype, for example, sugary-1 (su1) and sugary-2 (su2).

One combination of these mutant genes which has been found to possess utility is taught in U.S. Pat. No. 4,428,972 issued Jan. 31, 1984 to Wurzburg et al.

It has now been discovered that a plant having an amylose extender dull shrunken-1 (aedush1) homozygous genotype will produce starch having a high amylose content with a gelatinization temperature significantly lower than that of other high amylose starches with comparable amylose content. Specifically, it has been discovered that the starch of the present invention has a gelatinization temperature about 5.degree. C. lower than conventional high amylose starch of comparable amylose content.

It has also been discovered that the starch of the present invention has attributes which make it comparable to chemically modified starches; specifically crosslinked starches.

An advantage of such a novel starch is that it can replace chemically modified starches, thereby providing economic advantages.

In order to obtain substantially pure starch in accordance with the present invention, plants which produce edible starch and have either an amylose extender (ae), dull (du), or shrunken-1 (sh1) are crossbred to produce a plant having an amylose extender dull shrunken-1 (aedush1) homozygous genotype. The starch is then extracted from this plant. Both the crossbreeding step and the extraction step of the present invention are carried out in a conventional manner.

In order to prepare a sol in accordance with the present invention, a slurry is prepared which comprises water and an effective amount of starch extracted from a plant of the aedush1 genotype and the sol subject to a cooking step. The slurry is cooked as necessary to provide a thickener composition which exhibits properties comparable to sols made from conventional high amylose starch of comparable amylose content except that less energy is needed to cook the starch of the present invention compared to conventional high amylose starches. If the starch has been made "cold water swellable", then the cooking step can be eliminated. The preferred amount of starch used in the slurry constitutes about 1 to 20% by weight of slurry. Generally, cooking entails raising the temperature of the slurry to above about the gelatinization temperature of the starch and subjecting the starch to enough shear such that the granules rupture and a paste is formed. It is not necessary that all the granules rupture. Conventional high amylose starches are cooked with special equipment such as jet cookers. Using starch of the present invention, such special equipment is not necessary.

A sol or a thickener composition of the starch of the present invention is added to a foodstuff in a conventional manner in order to provide the benefits of high amylose starch to the foodstuff.

Alternatively, starch of the present invention is mixed with a foodstuff in a slurry comprising water and starch of the present invention is mixed with foodstuff and the resulting mixture cooked to produce a thickened foodstuff and to provide the benefits of a high amylose starch to the foodstuff.

In order to replace high amylose or chemically modified starches, a ratio of about 1:1, starch of the present invention:conventional starch, may be employed. Larger or smaller amounts of the starch of the present invention may be used to replace the conventional starch.

The term starch as used in the specification and claims means not only the substantially pure starch granules as extracted from a starch bearing plant but also grain products of the starch granule such as flour, grit, hominy and meal.

The term amylose extender dull shrunken-1 or aedush1 genotype as used in the specification and claims means not only the aedush1 homozygous genotype, aeaedudush1sh1, which has been obtained by standard plant breeding techniques, but also the aedush1 genotype which has been moved to another portion of the plant genome by translocation, inversion or any other method of chromosome engineering to include variations thereof whereby the disclosed properties of the starch of the present invention are obtained.

The term high amylose starch as used in the specification and claims means starch having an amylose content of about 50% and above. Conventional cereal and tuber and root starches have an amylose content of about 20% while waxy starch has an amylose content less than about 1%. These percents are by weight based on the total weight of amylose and amylopectin in a starch granule.

Any plant source which produces edible starch and which can be crossbred to produce a plant having an aedush1 homozygous genotype may be used. Amylose extender (ae) has been found in cereal grains such as maize and barley. The shrunken-1 (sh1) gene is also obtained from cereal grains such as maize. The dull (du) genotype has been located in maize. Maize is the preferred plant source. The shrunken-1 gene is reported to be located on chromosome of the maize chromosomes. Amylose extender (ae) is reported to be located on chromosome 5 in maize and dull (du) is reported to be located on chromosome 10 in maize. These locations are published in the open literature.

Generally, to obtain a starch bearing plant with both triple recessive mutants of the ae, du and sh1 genotype, plants having ae mutant, du mutant and sh1 mutant are crossbred to produce the triple mutant aedush1 and thereafter inbred to obtain a plant homozygous in aedush1. After the homozygous aedush1 genotype is obtained, standard breeding techniques are used to obtain hybrid vigor. Hybrids are preferred because of their high starch yield compared to inbred lines. The method of crossing plants and of obtaining specific genotypes in the offspring as well as breeding to obtain hybrid vigor is well known.

Extraction of starch from the plant is well known and typically entails a milling process. In accordance with the present invention, a wet milling process is used to advantage to extract the corn starch from the corn kernels. Corn wet milling comprises the steps of steeping and grinding the corn kernel and then separating the starch from the other components of the kernel. Prior to steeping, the kernels are subjected to a cleaning process to remove any debris which may be present. This cleaning process is usually done at the wet milling plant. The kernels are then steeped in a steep tank where the kernels are contacted with a countercurrent flow of water at an elevated temperature of about 120.degree. F. and containing sulfur dioxide in an amount between about 0.1 to about 0.2% by weight water. The kernels are maintained in the steep tank for about 24 to 48 hours. Next, the kernels are dewatered and subject to a first set of attrition type mills.

The first set of mills generally grind and rupture the kernels causing the germ, corn oil, to be released from the rest of the kernel. A typical attrition type mill used in commercial wet milling processes is sold under the brand name Bauer. The released germ is then separated from the other parts of the kernel by centrifugation. Throughout the grinding steps of the wet milling process the kernel and the kernel components are maintained in a slurry of about 40% by weight solids.

The remaining kernel components which include starch, hull, fiber and gluten, are subjected to a second set of attrition type mills such as the Bauer Mill, to further grind the components and separate the hull and fiber from the starch and gluten. Hull and fiber are generally referred to as bran. Washing screens are used to separate the bran from the starch and gluten. The starch and gluten pass through the screens while the bran does not.

Next, the starch is separated from the protein. This step is done either by centrifugation or by a third grind followed by centrifugation. A commercial centrifugation separator suitable for the present process is the Merco centrifugal separator.

The slurry which contains the starch granules is then dewatered and the resulting granules washed with fresh water and dried in a conventional manner preferably to about 12% moisture.

In this manner, the substantially pure starch of the present invention is extracted from a starch bearing plant of the aedush1 genotype.

Alternatively to the drying step, the starch may be left in suspension and subject to further modification.

Modification of the starch may also be performed on the dried starch. Typically, in order to change the physical and/or chemical structure of the starch granule, the starch is subject to any one or more of eight general treatments. These treatments comprise bleaching, thin boiling, acid treatment, enzyme treatment, dextrinization or dry roasting, etherification, esterification, and crosslinking Starches which have been treated by any one or more of these eight treatments listed above are conventionally referred to as chemically modified starch.

Bleaching, often referred to as oxidation, is a modification which does not appreciably alter the granular structure of the starch. Oxidation does, however, tend to lighten the color of the granules and reduce the viscosity of the starch paste.

In order to bleach the starch of the present invention, a slurry of starch is prepared of about 5 to about 40% by weight starch. To the slurry sodium hypochlorite is added with about 6% available chlorine (free chlorine) and the slurry is held at about 110.degree. F. for between about 1 to about 20 hours. The slurry is then neutralized with sodium bisulphite and the resulting granules are dewatered, washed and dried in conventional manner.

Such modification makes the starch of the present invention suitable for laundry starch, paper coating and as a textile size.

In order to produce a thin boiled starch of the present invention, a slurry of starch is prepared of about 5 to about 40% by weight starch. To this slurry, a mineral acid is added and allowed to react with the starch for about 1 to about 100 hours at about 90 to about 120.degree. F. with constant agitation. Such a reaction is done below the gelatinization temperature of the starch. Subsequently, the solution is neutralized, dewatered, washed and dried in conventional manner.

Thin boiling leaves the granules intact and produces a starch product which has a slight reduced viscosity compared to the non-thin boiled starch. If partial or total destruction of the starch granule is sought, the granule may be subjected to acid treatment.

In order to acid treat the starch of the present invention, a slurry of starch about 5 to about 40% by weight starch is prepared. This slurry is reacted with acid, generally a strong acid, at a temperature above gelatinization temperature. Such a procedure is preferably carried out by jet cooking the slurry through a conventional jet cooker with or without acid already in the slurry and then allowing the slurry to react with the acid, adding acid if needed, for a desired period of time or until the desired dextrose equivalent (DE) is reached. The DE is roughly proportional to the length of time for the reaction. Generally, such jet cooking destroys the starch's granular structure.

After acid treatment, the resulting slurry is neutralized, dewatered and dried. Such product may also be subject to conventional carbon treatment and filtration prior to dewatering and drying. Another treatment which degrades the granular structure is enzyme treatment.

In order to enzyme treat the starch of the present invention, a slurry of starch is made up having about 5 to about 40% by weight starch. To this slurry, enzyme is added at the optimum pH and temperature for the enzyme. Some advantage is found by first jet cooking the slurry to open up the starch granules, cooling the slurry to optimum temperature for the enzyme and then adding the enzyme. If the enzyme is jet cook stable then the enzyme can be added to the slurry prior to jet cooking. The slurry may also be treated with acid first to a low DE and then enzyme treated. After enzyme treatment, the product is dewatered and dried. Alternatively, the product may be subject to conventional carbon bleaching and filtration prior to concentration and/or drying.

In order to dextrinize or dry roast the starch of the present invention, acid is added to dry starch granules and the mixture is heated to a temperature of about 250.degree. to about 350.degree. F. for about 3 to about 72 hours. The product, once removed from the heat, is sold as is. The preferred acids are hydrochloric, phosphoric and any mineral acid. Such a method causes the partial breakdown of the granular structure.

In order to etherify the starch of the present invention, a slurry of starch is made up having about 5 to about 40% by weight starch. The pH of the slurry is adjusted to about 10 to about 12 preferably with sodium hydroxide. Next, an etherification agent such as ethylene oxide or propylene oxide is added to the slurry in an amount of about 1/2 to about 25% depending on the desired degree of substitution. The reaction conditions are held for about 5 to about 30 hours at about 70.degree. to about 120.degree. F. The slurry is then neutralized with any known acid, dewatered, washed and dried.

In order to crosslink the starch of the present invention, a slurry of starch is made up of about 5 to about 40% by weight starch. The pH of the slurry is adjusted to about 8 to about 12 preferably with sodium hydroxide. Optionally, a salt may be added to the slurry to affect swelling of the granules. Then the slurry is reacted with a crosslinking agent such as phosphorous oxychloride, trimetaphosphate salt, or epichlorohydrin at about 70 to about 120.degree. F. for about 1/2 to about 5 hours. The length of time of the reaction will depend on the amount of crosslinking agent used and the specific crosslinking agent chosen.

In order to esterify the starch of the present invention, a slurry of starch is prepared having about 5 to about 40% by weight starch. The pH of the slurry is then adjusted to about 8 to about 10 and an esterification agent is added to the slurry such as vinyl ester, acetyl halides, acid anhydrides like acetic anhydride, or succinic anhydride. The esterification agent is added slowly while maintaining the pH of the slurry. The reaction is continued for about 1/2 to about 5 hours at about 80 to about 120.degree. F. Once the reaction is completed to the desired degree of substitution, the slurry is neutralized, dewatered, washed and dried.

Any combination of these modifications may be employed on starch of the present invention.

It has been found that a sol comprising water and an effective amount of starch extracted from a plant of an aedush1 genotype exhibits thickening characteristics which makes the sol a good commercial thickener composition. Such thickener compositions are especially useful in foodstuffs.

The sol is prepared by forming a slurry of water and starch of the present invention and subsequently cooking the slurry thereby forming a paste. Preferably, the sol contains the starch of the present invention in the amount of about 1 to about 20% by weight total sol. The slurry is cooked at a temperature of about 90.degree. C. and above to provide thickening characteristics prior to adding to the foodstuff. Cooking time is about 10 minutes. The sol in accordance with the present invention need not be cooked if the starch has already been subjected to a process which makes it cold water swellable. Cooking generally comprises raising the temperature of an aqueous slurry of the starch of the present invention to the gelatinization temperature of the starch and subjecting the starch to shear such that the starch granules rupture and form a paste.

In order to prepare the thickened foodstuff, a sol made in accordance with the present invention is combined with a foodstuff and the composition is cooked to the necessary degree to provide a thickened foodstuff. Conventional mixing is employed to combine the sol with the foodstuff. Cooking of the sol and foodstuff composition is also carried out in a conventional manner.

Alternatively, starch of the present invention is mixed with the foodstuff or a slurry comprising the starch of the present invention and water is mixed with a foodstuff and the resulting mixture is cooked to the desired degree to obtain a thickened foodstuff. When the starch itself or a slurry containing the starch itself is mixed with a foodstuff, the resulting mixture must be cooked in order to provide a thickened foodstuff. The mixing as well as the cooking is accomplished in a conventional manner. Cooking is carried out at a temperature of about 90.degree. C. and above. Cooking time is about 10 minutes but may vary depending on the amount of foodstuff present and the amount of shear that the mix is subject to during cooking.

Such a thickener composition provides high amylose characteristics, such as good gel strength, while lowering the temperature needed for cooking as compared to conventional high amylose starches.

These and other aspects of the present invention may be more fully understood with reference to the following examples.

This example illustrates the extraction of the starch of the present invention from an aedush1 maize kernel produced by conventional crossbreeding and tests the starch to determine its various characteristics. The tests as well as the results obtained therefrom are given in Table I below. The extraction process as well as the test procedures followed are outlined following Table I below:

In order to perform the crossbreeding process, typically maize plants having the mutant gene ae were cross pollinated with maize plants having the mutant gene du which were in turn cross pollinated with maize plants having the mutant gene sh1. From the mature ears of some of these plants, kernels having aedush1 homozygous genotype were produced. Such kernels were used to produce starch in accordance with the present invention and to provide seed for future maize plants of the aedush1 homozygous genotype.

The following extraction process was used to extract the starch from the kernel. Sample A was grown in a dent corn background, OHIO 48, while Sample B was grown in a dent corn background, W64A.

Steeping was carried out by adding maize kernels to water having a 0.2% SO.sub.2 content and holding the temperature of the steep water at 50.degree. C. for 48 hours. The steep water was circulated through the steep container. After the 48 hours of steeping, the kernels were dewatered and washed with water.

A mixture of 1:1 kernels to water in a weight ratio was prepared and added to a Waring blender equipped with a dull blade. The Waring blender was put on grind for one minute to mill the starch. The resulting mash was poured onto a 40 mesh screen and what passed through the 40 mesh screen was passed through a 200 mesh screen and subsequently through a 325 mesh screen. The resulting filtrate contained starch and protein. That which did not pass through the first 40 mesh screen was put back into the Waring blender with water in a 1.1 weight ratio. This time a sharp blade was used and the Waring blender was set for one minute on grind. The resulting mash was then subject to a 40 mesh screen and then the filtrate was subjected to a 200 mesh screen and finally to a 325 mesh screen. The final filtrate from both the dull blade grind and the sharp blade grind were dewatered and contained starch and protein. The starch and protein were reslurried and subjected to up to three separate centrifuges to separate the starch from the protein.

The final starch was then filtered and dried in an oven at 110.degree. C. overnight to a moisture content of approximately 10%.

In this manner, starch was extracted from corn kernels in the lab.

The percent protein was determined by a standard Corn Refiners Association (CRA) method (Kjeldahl method).

The percent oil was also done using a standard CRA method by extracting the oil from dry, ground kernels using carbon tetrachloride for sixteen hours.

The percent amylose was determined using standard calorimetric iodine procedures wherein the starch is first gelatinized with sodium hydroxide and then reacted with an iodine solution and the resulting sample measured using a spectrophotometer in a 1 cm cell at 600 nm against a blank of 2% iodine solution.

The DSC gelatinization temperature was measured using a scanning calorimeter manufactured by Mettler Model No. 300 using a 30% solid starch following the procedure outlined in the owner's manual for that model.

Two Brabender amylograms were run; one in a non-acid environment and one in an acid environment. Both were run at 12% solids using a 90 gram sample with 125 gram cartridge at 100 RPM for sample A while the non-acid Brabender was run at 12% and the acid at 51/2% for sample B. The exact procedure used is outlined in the Amylograph Handbook of the American Association of Cereal Chemists, 1982 edition at pages 17 and 18. The respective paddle for the 90 gram cup was used. The difference between the acid and the regular Brabender was that 1.56 grams of glacial acetic acid was added to the sample to drop the pH of the sample to about 3 prior to running of the samples. Such acid test is used to show stability in acid conditions.

The initial rise was the temperature at which the pen moves away from the baseline.

Both acid and regular samples were subjected to identical heat profiles. The sample started at room temperature and the rapid heat mode of the instrument was used to heat the sample to 50.degree. C. Once 50.degree. C. was reached the instrument was set at a controlled rate of heating, 11/2.degree. C./minute, until a temperature of 95.degree. C. was reached. The sample was then held at 95.degree. C. for 30 minutes. During this period of heating, the highest viscosity obtained by the sample was labeled Heating Peak. The Heating Final was the last viscosity obtained by the sample at the end of the heating cycle. Next, the sample was cooled at 11/2.degree. C. to a temperature of 50.degree. C. The sample was then held at 50.degree. C. for 30 minutes. The largest viscosity measurement taken during this cooling cycle was the Cooling Peak and the final viscosity at the end of the cooling cycle was the Cooling Final.

Brabender curves are a well known tool for determining characteristics of starch.

Brookfield viscosities, another well known measurement used for analysing starch was measured for the starch of the present invention in Table I above. In order to run this test, the starch slurry as it came from the regular, non-acid Brabender test was used for the Brookfield test.

A Brookfield viscometer Model RV was used following standard procedures to obtain these values. The tests were run at 50.degree. C. with each RPM being run for a twenty second time interval.

Hercules viscosities were run on a Kaltec Model No. 244RC (manufactured Aug. 31, 1975) following the procedure outlined in the operators manual. Each test was run at 75.degree. F. using bob A. A 25 gram sample of starch paste as obtained from the acid Brabender was used for this test. Hercules viscosities measured high shear resistance of starch in an acid environment.

This example illustrates the high amylose content and low gelatinization temperature of the starch of the present invention in maize as compared to conventional high amylose starch. The results are listed in Table II below.

Sample 1 was a commercial product sold by American Maize-Products Company, Hammond, Ind. The percent amylose and the gelatinization temperature for Sample 1 above are mean values determined by random sampling of product. The 99% confidence level for percent amylose and gelatinization temperature are 25.9 to 29.3 and 68.7 to 72.9 respectively.

AMY V and AMY VII are commercial high amylose starches sold by American Maize-Products Company, Hammond, Ind. The percent amylose and the gelatinization temperatures in Table II above are mean values determined from a random sampling of product. The 99% confidence interval for the percent amylose in AMY V and AMY VII was 53.4 to 62.5 and 65.5 to 73.8 respectively. The 99% confidence interval for the gelatinization temperature for AMY V and AMY VII was 72.8 to 84.4 and 83.1 to 90.8 respectively. Both AMY V and AMY VII were grown in native maize.

Starch Sample 4 corresponds to Sample B of Example 1 above.

The method for determining both the percent amylose and the gelatinization temperature was that outlined in Example 1 above.

It is readily apparent from Table II above that the starch of the present invention had a high amylose content, above about 50%, while also a low gelatinization temperature, about 70.degree. C. The gelatinization temperature of the starch of the present invention is about 5.degree. C. lower than comparable high amylose starches. In fact, the gelatinization temperature of the starch of the present invention is comparable to common corn starch. Thus, the use of the starch of the present invention can lead to greater economic savings due to the lower energy need to gelatinize the starch.

This example illustrates the snynergistic nature of the starch of the present invention. The results of this example are listed in Table III below.

Sample 1 is the same as Sample 1 of Table II above. W64A and OHIO 48 have been identified in Example 1 above.

The starch of Samples 2-7 above were extracted from corn kernels in the same manner as outlined in Example 1 above.

Samples 8 and 9 correspond to Samples A and B respectively of Example 1 above.

The method for determining percent amylose and gelatinization temperature are those outlined in Example 1 above.

It is apparent that amylose content of the starch of the present invention has a higher percent amylose than the average of the individual starches while having a gelatinization temperature equal to the average of the individual component starches.

This example illustrates the gel strength of a sol made from the starch of the present invention compared to a sol made from a commercial high amylose starch, AMY V. The results of the test are reported in Table IV below.

In order to perform the gel strength test reported in Table IV above, sols were prepared by mixing water with starch and subjecting the slurry to a non-acid Brabender and subsequently a non-acid Brookfield viscosity test in accordance with Example 1 above. Both sols were prepared at 12% solids. Portions of these sols were added separately to 4 ounce jars into which a plunger was placed. The sols were then allowed to stand at ambient conditions for 24 hours. Gel strength was measured by determining the force needed to remove the plunger from the sol. In both cases the plunger did not pull out of the sol; rather, the plunger and gelatinized sol pulled out of the 4 ounce jar.

This example illustrates that the gel strength of a sol made in accordance with the present invention is comparable to conventional high amylose starch sols.

This example illustrates preparing a thickener composition in accordance with the present invention.

The starch of the present invention as extracted in Example 1 above is mixed with water in an amount to produce a slurry having 10% by weight starch. The sol has a short texture and a bland taste. The sol when cooked at about 90.degree. C. for ten minutes produces a thickener composition. This is especially synergistic because typically sols of high amylose starch are cloudy.

This example illustrates making a gum candy using the starch of the present invention.

The following ingredients and procedure is used:

All ingredients are mixed and then cooked to 340.degree. F. using conventional equipment such as a jet cooker. The cooked slurry is then poured into candy molds and allowed to solidify.

This example illustrates making a bavarian cream pie using starch of the present invention.

The following ingredients and procedure is used:

All of the pie filling ingredients except for egg yolks are combined and cooked at 195.degree. F. for 3 to 5 minutes. Then the ingredients are cooled to 120.degree. F. with constant stirring. Next egg yolks are added and the admixture well blended. This mixture is then added to a conventional pie crust and allowed to cool to room temperature before serving.

This example illustrates making a barbecue sauce using the stock of the present invention. Table VII below lists the ingredients and the procedure for making the sauce.

All the ingredients are combined and then cooked at 195.degree. to 200.degree. F. for 3 to 5 minutes.

Although the use of the present invention has been disclosed primarily with respect to foods, this is not deemed to limit the scope of this invention. The present invention can be used in other fields of industry such as paints, plastics, paper, wallboards.

It will be understood that the claims are intended to cover all changes and modifications of the preferred embodiments of the invention herein chosen for the purposes of illustration which do not constitute a departure from the spirit and scope of the invention.