Cellulose, a polysaccharide consisting of beta-1,4-linked glucose formed by natural processes (Applied Fiber Science, F. Happey, Ed., Chapter 8, E. Atkins, Academic Press, New York, 1979), has become the preeminent fiber for use in manufactured textiles, films and resins.
Cellulose and starch exhibit properties that are determined by the nature of their linkage pattern. Starch or amylose consisting of alpha-1,4 linked glucose are not useful for fiber applications because it is swollen or dissolved by water. Cellulose, on the other hand, has a beta-1,4 linkage which provides the crystalline and hydrophobic qualities making cellulose a good structural material. Thus, cellulose is commonly used for textile applications like cotton fiber.
Cellulosic fibers such as cotton and rayon increasingly present sustainability issues with respect to land use and environmental imprint. This may be a significant factor leading to increased level of research into textiles containing polyester fiber blends with cellulosic materials and more sustainable alternatives for cellulosic-derived materials.
Driven by a desire to find new structural polysaccharides using enzymatic syntheses or genetic engineering of microorganisms or plant hosts, researchers have discovered polysaccharides that are biodegradable, and that can be made economically from renewable resource-based feedstocks. One such polysaccharide is poly alpha-1,3-glucan, a glucan polymer characterized by having alpha-1,3-glycosidic linkages. This polymer has been isolated by contacting an aqueous solution of sucrose with a glucosyltransferase enzyme isolated from Streptococcus salivarius (Simpson et al., Microbiology 141:1451-1460, 1995). Films prepared from poly alpha-1,3-glucan tolerate temperatures up to 150° C. and provide an advantage over polymers obtained from beta-1,4-linked polysaccharides (Ogawa et al., Fiber Differentiation Methods 47:353-362, 1980).
U.S. Pat. No. 7,000,000 disclosed the preparation of a polysaccharide fiber comprising hexose units, wherein at least 50% of the hexose units within the polymer were linked via alpha-1,3-glycosidic linkages using an S. salivarius gtfJ enzyme. This enzyme utilizes sucrose as a substrate in a polymerization reaction producing poly alpha-1,3-glucan and fructose as end-products (Simpson et al., 1995).
The production of poly alpha-1,3-glucan for commercial applications using sucrose and gtf enzymes requires a high yield process that produces minimal amounts of by-product such as leucrose as well as the ability to control the polymer length or molecule weight of the resulting poly alpha-1,3-glucan.
Castillo et al. (Journal of Biotechnology 114:209-217, 2004) disclosed that the inclusion of 2-methyl-2-propanol (tert-butyl alcohol) in a reaction for producing levan resulted in levan having an increased molecular weight profile compared to the molecular weight profile of levan made without using tert-butyl alcohol.
Masanori et al. (Japanese Pat. Appl. Publ. No. P2000-175694A) disclosed that the inclusion of dimethyl sulfoxide in a reaction for producing mutan resulted in the production of mutan with increased molecular weight compared to the molecular weight observed in reactions lacking dimethyl sulfoxide. Thus, increasing the molecular weight of certain polysaccharide polymers is possible under certain reaction conditions.
Alternatively, decreasing the molecular weight of polysaccharide polymers is another means by which to control the molecular weight. Accordingly, processes for producing poly alpha-1,3-glucan having reduced molecular weight are desirable as another approach to producing a polysaccharide polymer of desired molecular weight.