Starch of the Duh Genotype and Products Produced Therefrom

This invention relates to starch and more particularly to starch which has been extracted from a plant having a dull horny (duh) 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 a dull horny (duh) homozygous genotype will produce a starch having characteristics which are comparable to chemically modified starch.

The advantage of such a novel starch is that it may replace chemically modified starches. This provides economic advantages.

One area of modified starches that has received a great deal of attention is the area of canning starches or thin-thick starches. These starches have a particular utility in canning. In a canning process high temperatures are attained rapidly and maintained for a period of time to accomplish sterilization of the foodstuff. Thin-thick starches are added to the foodstuff to provide viscosity to the foodstuff. The name thin-thick is given to these starches because of their viscosity behavior, low or thin viscosity initially to allow for rapid heat penetration to facilitate sterilization, increased or thick viscosity after sterilization to add body to the canned foodstuff. The term canning as used in this specification and claims means the act of preserving by heat whether the heat is applied before or after the packaging of the food and regardless of the form of the package. Canning includes, for example, pouch packaging, canning, aseptic pack, and retorting. Generally, thin-thick starches are chemically modified by hydroxypropylation to a specific degree of substitution followed by crosslinking to a specific level. A thin-thick starch specifically developed for retorting is taught in U.S. Pat. No. 4,120,983 issued Oct. 17, 1978 to del Valle et al. The starch taught by the '983 patent is a hydroxypropylated, epichlorohydrin crosslinked tapioca and corn starch derivative.

It has been found that starch of the present invention possesses properties which make it suitable as a starch in canning operations especially in acid environments which are typically present in such foods as tomato paste, chili, fruit and the like. Another area that the starch of the present invention is suitable in is microwaveable preprocessed foods in an acid environment.

FIG. 1 is an amylogram of the starch of the present invention at 12% solids in an acid environment.

In order to obtain substantially pure starch in accordance with the present invention, a plant which produces edible starch and has a dull (du) genotype is crossbred with a plant which produces edible starch and has a horny (h) genotype to produce a plant having a dull horny (duh) 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 duh genotype and the slurry is subjected to a cooking step. The slurry is cooked as necessary to provide a thickener composition. 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.

A sol or a thickener composition of the starch of the present invention is added to a foodstuff in a conventional manner.

Alternatively, starch of the present invention is mixed with a foodstuff or a slurry comprising water and starch of the present invention is mixed with a foodstuff and the resulting mixture cooked to produce a thickened foodstuff thereby providing the foodstuff with freeze-thaw characteristics in accordance with the present invention.

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

The starch of the present invention is employed as a thin-thick canning starch in an acid environment by mixing the starch, a slurry or a sol containing the starch of the present invention with a foodstuff suitable for canning. Generally, water is included in this mixture. Conventionally, the pH of the mixture is adjusted. The mixture is then sealed in a container and then subject to a canning process. During such canning process the contents of the container preferably reaches about 220.degree. F. and is held there for about 5 to about 25 minutes thereby sterilizing the contents of the sealed container. The amount of starch of the present invention employed in such a canning process is an effective amount and preferably between about 1% to about 20% by weight based on the total weight on the container's contents. The sol, slurry or starch of the present invention is conventionally mixed with the foodstuff.

Specifically, the starch of the present invention has been found to be of special advantage in an acid environment in canning, e.g. pH 3-6.

Another area that has been growing rapidly is microwaveable food, e.g. foods that are prepared by a commercial manufacturer and sold to the consumer. The consumer merely places the food into the microwave for heating. Due to the nature of the microwave, the starch used as a thickener in such preprocessed foods needs to have specific attributes which, in many cases, are different from conventional starches in the market today. The starch of the present invention has attributes which make it suitable for use in microwaveable preprocessed food.

The preferred attributes of a microwaveable starch is one that has an initial viscosity about 500 BU so that it provides some viscosity for initial processing purposes, and then drops to about 100 BU to allow for good heat penetration during sterilization by the manufacturer. Finally, during the cooling period after the sterilization, which typically calls for freezing, there should be a rise in viscosity to above the initial peak, e.g. above about 500 BU. This rise in viscosity, dip, then final rise is referred to as the "saddle effect".

FIG. 1 illustrates an amylogram of the starch of the present invention at 12% solids.

Preferably, the starch of the present invention is used in microwavable preprocessed food at an effective amount. The initial peak of about 500 BU is shown at 1 in FIG. 1, the dip or low viscosity is shown at 2 in FIGS. 1 and 3 shows the final rise in the viscosity. A starch which exhibits such a "saddle effect" is useful in microwaveable foods as well as in canning.

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 dull horny or duh genotype as used in the specification and claims means not only the duh homozygous genotype, duduhh, which has been obtained by standard plant breeding techniques but also the duh 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.

Any plant source which produces edible starch and which can be crossbred to produce a plant having a duh homozygous genotype may be used. It has been found that cereal grains such as maize have the mutants dull (du) and horny (h). Maize is the preferred plant source. The dull gene is reported to be located on chromosome 10 of the maize plant and the horny gene is reported to be located on chromosome 3 of the maize plant. These locations are published in the open literature.

Generally, to obtain a starch bearing plant with both double recessive mutants of the du and h genotype, a plant of a du mutant is crossed with a plant having a h mutant and thereafter inbred to obtain a plant homozygous in duh. After the homozygous duh 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 duh 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 the 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.degree. to about 120.degree. F. with constant agitation. Such a reaction is done below the gelatization 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 subjected 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.degree. 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.degree. 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 a duh 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 ten 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 ten minutes but may vary depending on the amount of foodstuff present and the amount of shear that the mix is subjected to during cooking.

To employ the starch of the present invention as a thin-thick starch, the starch of the present invention, a slurry or a sol containing the same is mixed with a foodstuff, placed in a sealed container and subject to a canning process in which the temperature of the container contents are held at a temperature above about 220.degree. F. for about 5 to about 25 minutes to accomplish sterilization.

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 a duh 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 du were cross-pollinated with maize plants having the mutant gene h. From the mature ears of some of these plants, kernels having duh 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 duh 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 subjected to a 200 mesh screen and subsequently 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 of kernels to water. 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 subject to three separate centrifuges to remove 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 colorimetric 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 l 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 51/2% solids using a 90 gram sample with 125 gram catridge at 100 RPM. 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 are 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 microwaveable attributes of the starch of the present invention. FIG. 1 was obtained following the procedure outlined in Example 1 above to obtain the acid Brabender. This example was run at 12% solids using a 90 gram sample in a 350 cartridge, otherwise the procedure of Example 1 was followed.

It is clear from the Brabender amylogram that the starch of the present invention has viscosity characteristics which make it essentially suited for use in foods intended for use in a microwave.

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 slurry when cooked at about 90.degree. C. for twenty minutes produces a thickener composition. The sol was short and firm.

This example illustrates using the present invention in canning in an acid environment.

A medium is prepared by mixing 8% starch of the present invention with 58% water, 0.5% salt, 18.5% corn syrup and 15% sugar. The pH of the system is adjusted with citric acid to about 3.5. This medium is then mixed with blueberries to obtain a final mixture that contains about 50-60% by weight mixed blueberries. The final mixture is placed in a container and sealed. The sealed container is then subjected to a retort process.

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.