Organic compounds -- part of the class 532-570 series – Organic compounds – Carbohydrates or derivatives
Reexamination Certificate
1999-05-04
2002-07-23
Gitomer, Ralph (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carbohydrates or derivatives
C536S123000, C536S123100, C536S124000, C435S097000, C435S101000
Reexamination Certificate
active
06423833
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process for preparing functional sugar polymers and an apparatus useful for the synthesis of such sugar polymers.
BACKGROUND OF THE INVENTION
Sugar polymers produced by microorganisms and plants, mainly straight and branched glucans and fructans, have a long history of applicability in food products as gums, fillers, bulk sources, and other similar usage. In addition to their uses in foods some of these sugars have long been purported to impart health benefits. See, McAuliffe, J., Hindsgaul, O.; “Carbohydrate Drugs—An Ongoing Challenge”,
Chemistry and Industry
, Mar. 3, 1997. More recently a growing number of these polymers (whether of plant, microorganism or mammalian origin), especially those having unique branching or containing other sugars, such as fucose, galactose, sugar amines, or sialic acid, have been cited as imparting a variety of health benefits (see, for example, U.S. Pat. No. 5,514,660). While a great deal is known concerning the specific use and functionality of many of the significant natural sugar polymers, the complexity of these compounds and the resultant difficulty and high cost of preparing structures which may not exist in nature has limited the knowledge of general structure/function or health benefit relationships. Sugar polymers are generally isolated from plants or microorganisms by extraction and purified by a variety of techniques. Significant work has been done to increase the availability and functionality and to decrease the cost of these polymers. This work has centered in the following areas:
Better sources of the plant sugars have been found through the discovery of new species, selective breeding, and genetic manipulation.
Improved processes to extract the sugar polymers have been developed.
The sugar polymers have been separated into discrete chain length fractions and/or “refined” to a tighter specification.
Simple chemical modifications to some plant sugars have been developed.
Work is ongoing and accelerating in all of these areas. One important area with significant on-going effort is the genetic modification of organisms to improve the production of the existing sugars or to make new sugars.
Methods to obtain sugar polymers without using plants are also known. Both chemical and enzymatic synthesis have been developed (see, for example, Whitesdie, G. M., et al.; “Enzyme-Catalyzed Synthesis of Carbohydrates”,
Tetrahedron
, 45(17), pp. 5365-5422, 1989). Chemical synthesis, while possible is hindered by three factors. First, each of the monomeric units has multiple reaction sites. In normal chemical synthesis multiple reactive sites always add complexity but with carbohydrates this complexity is extremely significant. A polymer with just four sugar “monomer” units, can be assembled in ~270,000 possible ways. This complexity can be overcome by selective blocking and de-blocking of reactive sites but only at the expense of low yield and high processing cost. Second, the inter-sugar bonds are very labile under typical processing conditions again limiting synthetic choices and, decreasing yields. Finally, many chemical reactions are not stereo-specific, creating a separation problem and further yield reductions. The net results are high cost and general lack of availability. Chemical synthesis is clearly appropriate for production of sugar polymers only when the product carries a very high value.
Processes that use enzymes as selective catalysts offer more promise for the synthetic production of sugar polymers. Recent advances in the identification and production of these enzymes, as well as systems in which to accomplish multi-step coupling reactions have reduced the cost of producing sugar polymers by many orders of magnitude. These techniques are applicable to both “natural” polymers and novel polymers based on coupling “natural” carbohydrate sub-units in new ways. Enzymes have been identified which allow coupling of inexpensive starting materials, such as sucrose, making this type of process potentially very inexpensive. Enzyme based production provides for both coupling and stereo selectivity which minimizes purification costs (see U.S. Pat. No. 5,288,637, Roth, S., “Apparatus for the Synthesis of Saccharide Compositions”; U.S. Pat. No. 5,180,674, Roth, S., “Saccharide Compositions, Methods, and Apparatus for Their Synthesis”; PCT/US92/10891, Roth, S., “A Method for Obtaining Glycosyltransferases”; PCT/US95/12317, Gotschlich, E. C., “Glycosyltransferases for Biosynthesis of Oligosaccharides and Genes for Encoding Them”; PCT/US94/07807, Roth, S., “A Method for Synthesizing Saccharide Compositions”). While these techniques allow great control of the coupling reactions, control of the chain length or branch distribution in polymers is not addressed.
An example of a sugar polymer is inulin. This polymer consists of fructose units, joined linearly in a &bgr;-[2-→1] fashion to a terminal &agr;-D-glucopyranosyl unit. In many plants inulin is a major energy storage carbohydrate. It is highly regarded as a naturally low calorie foodstuff, which can be used to provide bulk to high intensity sweeteners, as a soluble fiber source, as a fat replacer, and as a promoter of bifidus bacteria in the digestive tract. Inulin is commonly produced by extraction from plants, notably chicory and Jerusalem artichoke. The material extracted from these plants contains polymers with from 1 to over 60 fructose units attached to a terminal glucose unit. Polymer distributions vary with the plant source, the planting location, and the harvest time. While the crude extract has application, product with 3 to 10 fructose units provides the most “sucrose-like” performance. These polymers make ideal bulking agents and fiber sources as they have low caloric density, are bland, and have many of the functional attributes of sucrose. Shorter polymers, while functional, provide a disproportionate increase in calories and sweetness. Longer polymers are less water-soluble and have good fat replacer properties but decreased. sucrose replacement functionality.
Several approaches have been used to provide improved functionality and consistent inulin product over a growing season. The first approach involves using a plant source that contains relatively long chain inulin and using selective enzymes to reduce the chain size in a controlled manner. EP 440074 relates to the selective hydrolysis of long-chain inulins. This allows some control over seasonal variations at the cost of adding a process step and does not help to eliminate the high calorie, short chain products. Another approach is to fractionate the crude inulin into cuts with different functionality. While this solves the functionality and seasonal variation problems, it does so at the expense of creating by-products. This approach also provides for removal of short chain polymers. Since it only involves fractionation it adds no “foreign” substances to the product. The two approaches can be combined in several ways to optimize functional product recovery. In both of these cases the agricultural source is grown specifically for the inulin product with all the risks associated with any agricultural program. These approaches also present the problem of disposal of a large mass of unused vegetable material. Finally, except for very high use sugars such as sucrose, it is difficult to generate any economies of scale when growing a plant for a specific product.
Another method to produce inulin fructooligosaccharides is to build up the fructose polymer from an inexpensive fructose source, such as sucrose, using coupling enzymes. (See Jong Won Yun, “Fructooligosaccharides—Occurrence, Preparation, and Application”,
Enzyme and Microbial Technology
19:107-117, 1996, and U.S. Pat. No. 4,681,771). This approach suffers from inhibition of the enzymatic reaction by a by-product of the coupling, glucose, which limits the conversion of the sucrose feed, and the length of the chains produced. These inulin fructooligosaccharide compositions, commonly have an average chain len
Catani Steven J.
Laurenzo Kathleen S.
Navia Juan L.
Walkup Robert E.
Gitomer Ralph
Khare Devesh
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