Progress in bioproduction, characterization and applications of pullulan: a review

Pullulan is a biopolymer produced by various strains of the fungi Aureobasidium pullulans. It is made up of maltotriose units consisting of α-(1,6) and α-(1,4) glycosidic bonds. Pullulan was discovered by Bauer in 1938, characterized by Bernier in 1958 and named as ‘pullulan’ by Bender in 1959. Submerged fermentation is widely employed for pullulan production followed by downstream processing for recovery of pullulan. Factors such as nutrients, minerals, pH, temperature, surfactants, light intensity, and melanin intermediate affect its production. Various optimization methods such as Plackett Burman design, response surface methodology, and artificial neural networks have been utilised for enhancing the yield of pullulan. Pullulan yield as high as 62.52 g/L can be achieved using a 5 L fermenter under optimised conditions. It can be characterized by techniques such as nuclear magnetic resonance, Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy. The biopolymer has remarkable properties which makes it an ideal candidate to be used in various applications such as the biomedical and pharmaceutical sectors, cosmetics, food, and wastewater treatment. Pullulan’s applications can be expanded by chemically modifying to obtain grafted pullulan, polymer blends, nanocomposites and hydrogels which have been gaining importance in recent years. Over the years, many patents using pullulan have been granted for different applications worldwide. This review sheds light on all these aspects of pullulan including its future scope. Graphical abstract: (Figure presented.)