levels. It does not dissolve at high pH while it is soluble at lower pH ranges. This property makes chitosan a suitable tool for delivery applications. Chitosan, and their derivatives have found a number of pharmaceutical or biomedical applications. Although chitosan was mostly used as a diluent in tablet manufacturing, it was also proposed as a binder, lubricant, or potential disintegrating agent. The mucoadhesive properties of chitosan make it an attractive material for the local delivery of drugs in the oral cavity.
2.4.5 Xanthan
Xanthan gum, a complex copolymer produced by a bacterium, one of the first commercially successful bacterial polysaccharides to be produced by fermentation [168, 169]. In terms of production volume, xanthan gum is the most widely used microbial polysaccharide. Worldwide production is currently in the range of 10,000 to 20,000 tons. Xanthans have many applications such as in hydrogel, antibacterial and catalytic applications, in silver nano-particles, in medicinal and pharmaceutical applications [170]. It is used in drug release [171], wound healing [172], blended hydrogels for connective tissue regeneration [173], immobilized biocatalyst [174], edible coatings and many others. Xanthan gum is a HMW extracellular polysaccharide produced by the fermentation of the gram-negative bacterium Xanthomonas campestris. Companies such as ADM and Merck have recently announced the expansion of their xanthan production facilities. About 60% of the xanthan produced is used in foods, with the remaining 40% used in industrial applications. Food-grade xanthan costs about $8 to $10 per pound, while non-food grades sell for about $5 per pound. So far, only experimental samples of genetically modified xanthan have been produced.
2.4.6 Dextran
Dextran is the generic name of a large family of microbial polysaccharides that are assembled or polymerized outside the cell by enzymes called dextran sucrases. This class of polysaccharides is composed of building blocks (monomers) of the simple sugar glucose [169, 175–177]. It can be found as storage material in yeasts and bacteria. Dextrans are produced by enzymatic conversion of the feedstock sucrose. Most commercial dextran production uses the microorganism Leuconstoc mesenteroides. Cyclodextrins is used as a stabilizer and in edotoxin removal [178]. Dextran polymers have some medical applications. Dextrans were used for wound coverings, in surgical sutures, as blood volume expanders, to improve blood flow in capillaries in the treatment of vascular occlusion, and in the treatment of iron deficiency anemia in humans and animals.
Chemically modified dextrans such as dextran sulfate [179] have antiulcer and anticoagulant properties. Other modified dextrans such as Sephadex are used extensively in the separation of biological compounds. In the industrial area, dextrans are being incorporated into x-ray and other photographic emulsions. Dextran is used as a food-grade biopolymer, nanoparticles, hydrogel, and in transdermal delivery [180].
Dextran-hemoglobin compounds may be used as blood substitutes that have oxygen delivery potential and can also function as plasma expanders.
2.4.7 Pullulan
Pullulan is a non-toxic exopolysaccharide of fungi origin. It is non-toxic, non-immunogenic, non-mutagenic and non-carcinogenic [181]. It produced from Aureobasiduim pullulans [182]. Pullulan is biodegradable impermeable to oxygen, non-hygroscopic and non-reducing. Pullulan possesses oxygen barrier properties, good moisture retention and it inhibits fungal growth so it enhances the shelf-life. It is used in tissue engineering, molecular chaperones, plasma expender and surface modification. Pullulan is a linear polymer made of monomers that contain three glucose sugars linked together. For more than a decade, a Japanese firm, Hayashibara Biochemical Laboratories, has used a simple fermentation process to produce pullulan. Some feedstocks are used for this process, including the streams containing simple sugars. Pullulan can be chemically modified to produce a polymer that is either less soluble or insoluble in water. The thermal and ionic (electrical) properties of pullulans can also be altered.
It can be used as a food additive, providing bulk and texture. It is tasteless, odorless, and non-toxic. It does not break down in the presence of naturally occurring digestive enzymes and therefore has no caloric content. So, it can be used as a food additive in low-calorie foods and drinks, in place of starch or other fillers. In addition, pullulan inhibits fungal growth and has good moisture retention, and thus can be used as a preservative. Pullulan can also be used as a water-soluble, edible film for the packaging of food products. It is transparent, impermeable to oxygen, and oil- and grease-resistant. Foods can be either immersed in a solution of pullulan or coated by a polymer spray. After the pullulan coating is dried, an airtight membrane is formed. Pullulan is used as gold nanoparticles for cancer treatment, drug delivery and in controlled release of biopharmaceutical [183, 184].
2.4.8 Glucan
A common source for glucan is baker’s yeast, Saccharomyces cerevisiae, although it is also found in some other sources (bacteria, fungi, lichen, and higher plants, such as, barley). Large supplies of inexpensive yeast are available from both the baking and the brewing (brewer’s yeast) industries. Glucans are the most abundant polymers in yeast, making up approximately 12–14% of the total dry cell weight. Glucan is readily purified from yeast cells by using hot alkali treatment to remove all other cellular materials, thereby allowing recovery of the insoluble glucan material. Yeast glucan particles purified by this method contain both HMW and lower molecular weight polymers. Glucan is used as an immunosuppressive [185]. Glucan has been modified and applied in different applications such as hydrogels [32, 186], and a potential prebiotic [187], in supporting the treatment of viruses [188] and many others. Although glucans are being exploited mainly for their antitumor, anti-infectious, and radioprotective properties, they also have non-medical applications. Glucans resist breakdown when attacked by digestive enzymes, and thus can be used as non-caloric food thickeners. Other possible applications include use in sustained-release tablets, encapsulation of oxygen for mass transfer in fermentation reactions, and as a solid support material for chromatographic separations [189–193].
2.4.9 Gellan
Gellan is a complex polysaccharide having a four-sugar repeat unit (glucose–glucuronic acid–glucose–rhamnose). It is produced by the bacterium Pseudomonas elodea, which is derived from plant tissue. The properties of gellan can be easily modified. A hot caustic treatment of gellan yields a polymer that has the desirable characteristic of low viscosity at high temperature. Cooling gellan in various cations (such as, calcium) results in forming strong gels. Gellan is used to inhibit Plasmodium falciparum growth in the food industry, personal care products [194], pharmacy and medicine [194], hard capsule [195], drug delivery [196], microspheres [197], cell differentiation [198], microbeads [199], nanocomposites [200] and many others.
2.4.10 Pectin
Pectin is a water-soluble colloidal carbohydrate that occurs in ripe fruit and vegetables. Pectin is a family of complex polysaccharides present in the walls that surround growing and dividing plant cells. It is also present in the junctional zone between cells within secondary cell walls including xylem and fiber cells in woody tissue. Its traditional application is in making fruit jellies and jams. Pectin is an essential component in the initial growth and ripening process of fruit and is often a waste material from the food and fruit processing industry. Pectins are made either from apple pulp, byproducts of cider manufacture, or from the peel of citrus fruits such as limes, the preferred source, lemons or oranges, byproducts of fruit juice manufacture. Pectins have long been recognized as the main gel-forming agents in jams and fruit-based preserves. It was known for a time that polysaccharides can stabilize colloidal sols and suspensions. The simple addition of water-soluble pectate for example: usually the sodium salt will prevent aggregation and precipitation. Gels can be obtained by mixing gelatin and pectin into lipid in water emulsions. The results are low-fat margarines and other spread type products. Pectins are used in drug delivery and as a colloidal [201].
2.4.11 Gums
Gums are plant substances which can be dissolved or dispersed in water to form more or less viscous colloidal solutions