Organic compounds -- part of the class 532-570 series – Organic compounds – Carbohydrates or derivatives
Reexamination Certificate
2001-01-15
2003-05-27
Wilson, James O. (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carbohydrates or derivatives
C800S284000, C800S278000, C800S285000, C800S286000, C800S287000, C800S320000, C800S320100, C800S320300, C435S069100, C435S101000, C435S468000
Reexamination Certificate
active
06570008
ABSTRACT:
FIELD OF THE INVENTION
This invention is in the field of plant molecular biology. More specifically, this invention pertains to the modification of starch biosynthetic gene expression to produce starches in plants and seeds.
BACKGROUND OF THE INVENTION
Starch is a mixture of two polysaccharides, amylose and amylopectin. Amylose is an unbranched chain of up to several thousand &agr;-D-glucopyranose units linked by &agr;-1,4 glycosidic bonds. Amylopectin is a highly branched molecule made up of up to 50,000 &agr;-D-glucopyranose residues linked by &agr;-1,4 and &agr;-1,6 glycosidic bonds. Approximately 5% of the glycosidic linkages in amylopectin are &agr;-1,6 bonds, which leads to the branched structure of the polymer.
Amylose and amylopectin molecules are organized into granules that are stored in plastids. The starch granules produced by most plants are 15-30% amylose and 70-85% amylopectin. The ratio of amylose to amylopectin and the degree of branching of amylopectin affects the physical and functional properties of the starch. Functional properties, such as viscosity and stability of a gelatinized starch determine the usefulness and hence the value of starches in food and industrial applications. Where a specific functional property is needed, starches obtained from various crops such as corn, rice, potatoes or wheat may meet the functionality requirements. If a starch does not meet a required functional property, such as the need for stable viscosity under high temperatures and acidic conditions, the functionality can usually be achieved by chemically modifying the starch. Various types and degrees of chemical modification are used in the starch industry, and the labeling and use of chemically modified starches must meet government regulations.
Within the starch bearing organs of plants, the proportion of amylose to amylopectin and the degree of branching of amylopectin are under genetic control. For example, corn plants homozygous for the recessive waxy (wx) mutation lack a granule-bound starch synthase enzyme and produce nearly 100% amylcpectin. Corn plants homozygous for the recessive amylose extender (ae) mutation and uncharacterized modifier genes can reportedly produce starch granules that are approximately 80% to 90% amylose (see U.S. Pat. No. 5,300,145). The dull mutant of corn lacks a starch synthase distinct from that lacking in the waxy lines and has a starch characterized by more amylose and a larger proportion of shorter branches on the amylopectin molecule than normal starch.
Most cereal crops are handled as commnodities, and many of the industrial and animal feed requirements for these crops can be met by common varieties which are widely grown and produced in volume. However, there exists at present a growing market for crops with special end-use properties which are not met by grain of standard composition. Most commonly, specialty corn is differentiated from “normal” corn by altered endosperm properties, such as an overall change in the ratio of amylose to amylopectin as in waxy or high amylose corn, an increased accumulation of sugars as in sweet corn, or an alteration in the degree of endosperm hardness as in food grade corn or popcorn (Glover, D. V. and E. T. Mertz (1987) in
Corn: Nutritional Quality of Cereal Grains; Genetic and Agronomic Improvement
, R. A. Olson and K. J. Frey, eds. American Society of Agronomy, Madison Wis., pp. 183-336; Rooney, L. W. and S. O. Serna-Saldivar (1987) Food Uses of Whole Corn and Dry-milled Fractions, in
Corn: Chemistry and Technology
, S. A. Watson and P. E. Ramstead, eds. American Association of Cereal Chemists, Inc., St. Paul, Minn., pp. 399-429). The current invention offers the buyers of specialty grains a source of starch having properties distinct from waxy starch and offers farmers the opportunity to grow a higher value-added crop than normal or waxy corn.
Purified starch is obtained from plants by a milling process. Corn starch is extracted from kernels through the use of a wet milling process. Wet milling is a multi-step process involving steeping and grinding of the kernels and separation of the starch, protein, oil and fiber fractions. A review of the corn wet milling process is given by S. R. Eckhoff (1992) in the
Proceedings of the Fourth Corn Utilization Conference
, June 24-26, St. Louis, Mo., printed by the National Corn Growers Association, CIBA-GEIGY Seed Division and the United States Department of Agriculture. Wheat is also an important source of purified starch. Wheat starch production is reviewed by J. W. Knight and R. M. (1984) Olson in Starch:
Chemistry and Technology
2
nd
Edition., Academic Press. Eds. Whisler et al.
Starch is used in numerous food and industrial applications and is the major source of carbohydrates in the human diet. Typically, starch is mixed with water and cooked to form a thickened gel. This process is termed gelatinization. Three important properties of a starch are the temperature at which gelatinization occurs, the viscosity the gel reaches, and the stability of the gel viscosity over time. The physical properties of unmodified starch during heating and cooling limit its usefulness in many applications. As a result, considerable effort and cost is needed to chemically modify starch in order to overcome these limitations of starch and to expand the usefulness of starch in industrial applications.
Some limitations of unmodified starches and properties of modified starches are given in
Modified Starches: Properties and Uses
, O. B. Wurzburg, ed., (1986) CRC Press Inc., Boca Raton, Fla. Unmodified starches have very limited use in food products because the granules swell and rupture easily, thus forming weak bodied, undesirable gels. Chemical modifications are used to stabilize starch granules thereby making the starch suitable for thousands of food and industrial applications including baby foods, powdered coffee creamer, surgical dusting powders, paper and yarn sizings and adhesives. Common chemical modifications include cross linking, in which chemical bonds are introduced to act as stabilizing badges between starch molecules, and substitution in which substituent groups such as hydroxyethyl, hydroxypropyl or acetyl groups are introduced into starch molecules.
The use of chemically modified starches in the United States is regulated by the Food and Drug Administration (FDA). “Food starch-modified” starches may be used in food but must meet specified treatment limits, and “industrial starch-modified” starches may be used in items such as containers that come in contact with food and must also meet specified regulatory requirements; Code of Federal Regulations, Title 21, Chapter 1, Part 172, Food Additives Permitted in Food for Human Consumption, Section 172, 892, Food Starch-Modified, U.S. Government Printing Office, Washington, D.C. 1981; (a) Part 178, Indirect Food Additives, Sect. 178.3520, Industrial Starch-Modified. These regulations limit the degree of chemical modification by defining the maximum amount of chemical reagent that can be used in the modification steps. The levels of by-products in starch resulting from the modification process are also regulated. For example, propylene chlorohydrin residues in hydroxypropyl starch are of special concern (Tuschhoff, J. V. (1986) Hydroxypropylated Starches, in
Modified Starches: Properties and Uses
, O. B. Wurzburg, ed., CRC Press, Boca Raton, Fla., pp. 55-57).
In addition to its use as a purified ingredient, starch is an important component of whole flours, such as wheat flour, used in the production of breads, baked goods and pastas. Starch comprises between 50 and 70% of the weight of a wheat grain and its importance in the performance of wheat flours is well known in the art. Although the complex genetics of wheat has limited the variations in starch fine structure that is available in whole flours, the production of novel starch structures in wheat or other flours may result in improved performance of these whole flours in food product applications. Starch structure is also an important component of the
Broglie Karen E.
Lightner Jonathan Edward
E. I. du Pont de Nemours and Company
Wilson James O.
Young Josephine
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