Pullulan is a linear, water-soluble polysaccharide produced by the fungus Aureobasidium pullulans, consisting of maltotriose repeating units linked by α-1,4 and α-1,6 glycosidic bonds. It is prized for its excellent film-forming ability, non-toxicity, and biodegradability.
Molecular Structure
Pullulan is composed of linear chains of glucose units organized into maltotriose subunits (Glc-α1,4-Glc-α1,4-Glc) interconnected by α-1,6 glycosidic linkages every three glucose residues. This unique arrangement results in a flexible, random coil conformation with minimal branching. Molecular weights typically range from 104 to 106 Da, influencing its solubility and viscosity. The neutral charge and high molecular weight contribute to the formation of strong, transparent, and oxygen-impermeable films upon drying.
Production and Properties
Industrial-scale pullulan production is achieved through submerged fermentation of A. pullulans using carbon sources such as glucose, sucrose, or agro-industrial wastes like molasses. Fermentation conditions are typically optimized at pH 5–7 and temperatures of 25–30°C. Following fermentation, pullulan is recovered by ethanol precipitation and further purified to remove pigments such as melanin.
Key physicochemical properties include excellent water solubility (>50 g/L), low solution viscosity relative to branched polysaccharides, high tensile strength, thermal stability, biodegradability by pullulanase enzymes, and GRAS status granted by the FDA. These attributes support its widespread use across food, pharmaceutical, and biomedical sectors.
Biomedical and Pharmaceutical Applications
Pullulan is extensively utilized in drug delivery systems, including nanoparticles, hydrogels, and polymer–drug conjugates, enabling controlled and targeted release. Its biocompatibility and mucoadhesive properties make it suitable for oral and ocular formulations, as well as gene delivery vectors.
In tissue engineering, pullulan-based materials are employed for wound healing scaffolds and cell encapsulation matrices. Additionally, pullulan serves as an ideal material for capsule shells and nutraceutical coatings due to its excellent oxygen barrier properties and rapid dissolution behavior.
