No abstract

Pullulan is a linear glucosic polysaccharide produced by the polymorphic fungus Aureobasidium pullulans, which has long been applied for various applications from food additives to environmental remediation agents. This review article presents an overview of pullulan's chemistry, biosynthesis, applications, state-of-the-art advances in the enhancement of pullulan production through the investigations of enzyme regulations, molecular properties, cultivation parameters, and bioreactor design. The enzyme regulations are intended to illustrate the influences of metabolic pathway on pullulan production and its structural composition. Molecular properties, such as molecular weight distribution and pure pullulan content, of pullulan are crucial for pullulan applications and vary with different fermentation parameters. Studies on the effects of environmental parameters and new bioreactor design for enhancing pullulan production are getting attention. Finally, the potential applications of pullulan through chemical modification as a novel biologically active derivative are also discussed.

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Bacterial cellulose (BC) demonstrates unique properties including high mechanical strength, high crystallinity, and high water retention ability, which make it an useful material in many industries, such as food, paper manufacturing, and pharmaceutical application. In this study, different additives including agar, carboxymethylcellulose (CMC), microcrystalline cellulose, and sodium alginate were added into fermentation medium in agitated culture to enhance BC production by Acetobacter xylinum. The optimal additive was chosen based on the amount of BC produced. The produced BC was analyzed by using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), thermogravimetric analysis (TGA), and dynamic mechanical analysis (DMA). Among the evaluated additives, CMC yielded highest BC production (8.2 g/L) compared to the control (1.3 g/L). The results also indicated that CMC-altered BC production increased with CMC addition and reached saturation around 1%. The variation between replicates for all analysis was \5%. From XRD analysis, however, the crystallinity and crystal size decreased as CMC addition increased. FESEM results showed CMC-altered BC produced from agitated culture retained its interweaving property. TGA results demonstrated that CMC-altered BC had about 98% water retention ability, which is higher than BC pellicle produced with static culture. CMC-altered BC also exhibited higher T max compared to control. Finally, DMA results showed that BC from agitated culture loses its mechanical strength in both stress at break and Young's modulus when compared to BC pellicle. This study clearly demonstrated that addition of CMC enhanced BC production and slightly changed its structure.