Starch

Starch is a carbohydrate that is synthesized in the organs of plants as a reserve food supply for periods of dormancy, germination, and growth [25]. Starch is the second most abundant "renewable" substance, after cellulose. Starch can be considered a condensation polymer of glucose consisting of two types, amylose, a linear-chain molecule of a-l,4-linked D-glucose, and amylopectin a branched polymer of a-1,4-linked D-glucose with a 1,6-linked D-glucose branched. Due to its function as a food storage, starch is readily biodegraded through enzyme-catalyzed hydrolysis by a number of enzymes [26]:

Typically, in nature, the amylopectin is semicrystalline and the amylose amorphous. Various processing techniques have been developed resulting in reducing or eliminating the amylopectin crystallinity and resulting in amylose complexa-tion [27]. The most notable of these technologies are the production of destructur-ized starch and thermoplastic starch. Destructurized starch, originally developed by Warner Lambert and currently owned by Novamont, is claimed to involve the use of water, typically greater than 5%, and mechanical shearing to form a more easily processable structure [28]. Thermoplastic starch is claimed to utilize a plasticizer such as glycerol in a "substantially water-free" starch to produce a thermoplastically processable starch and is currently produced by Biotech in Germany [29]. Earthshell has developed a composite material consisting of starch, calcium carbonate, and cellulose fibers for use in disposable food service items. Novamont in Italy produces starch and vinyl alcohol copolymer blends with starch contents greater than 60% under the trademark Mater-Bi [30, 31]. These materials are available in commercial grades suitable for blown film, injection molding, blow molding, thermoforming, and extrusion and are reported to be totally biodegradable and insoluble in water [31].

Konjac Konjac is a natural polysaccharide found in plant tubers from Amor-phophallus konjac and produced commercially by FMC (Philadephia, PA). Konjac is a copolymer of glucose and mannose (1:1.6) linked ft -1.4 with random acetylation of approximately ^ monomer units. The polymer is water soluble and as such the applications are limited. Chemical modifications of the konjac as well as liquid crystalline properties have been reported [32].

Amylose

Konjac

Konjac

Mannose

Glucose

Mannose

Glucose

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