Pullulan: benefits and Hyper-Production

Pullulan is a valuable and renewable exopolysaccharide (EPS) synthesized by the yeast-like fungi Aureobasidium. It comprises repeating maltotriose subunits (three glucoses linked via two α-(1→4) glycosidic bonds) linked via α-(1→6) glycosidic bonds, which impart unique physico-chemical properties, including water solubility, adhesive ability, structural flexibility and elasticity, film-forming ability, oxygen impermeability, biocompatibility, and biodegradability. Most yeasts with the ability to produce pullulan are generally regarded as safe (GRAS). Notably, pullulan has gained approval as an ingredient in foods and drugs in Japan, USA, Europe, and China, and as a fresh-keeping agent and stabilizer.  Moreover, pullulan-based capsule shells are also considered safe and manufactured by reputable companies, such as Hayashibara Co., Ltd. (Okayama, Japan) and Shandong Kangnaxin Biotechnology Co. Ltd. (Weifang, China).  Nowadays, pullulan and its derivatives have extensive applications in various sectors, including food, packaging, biomedicine, cosmetics, and environmental remediation.

Pullulan has oxygen barrier properties, excellent moisturising properties and also prevents fungal growth. These properties make it an excellent food preservation substance and it is widely used in the food industry. It shows activity against enzymes such as amylase, glucose oxidase, invertase, β-glucosidase and a small amount of protein hydrolase. Branched-chain starch is extremely soluble in water, so it is used as a carrier for drugs and helps to regulate delivery into the plasma. Pullulan polysaccharides can be chemically altered to produce derivatives with variable solubility or modified polymers that are completely insoluble in water and therefore have a wide range of applications.

Benefits of Pullulan in Cosmetics

Pullulan is a multifunctional skin care ingredient in the cosmetic field with moisturising and antioxidant properties. It is also used as a "carrier" for other skincare actives, helping to deliver the active ingredients. Research has shown that branched starch has the potential to help strengthen the skin's microbiota; providing temporary mechanical support for the skin's underlying structure. It also helps to provide a protective skin barrier, forming a film on the skin and extending the life of make-up.

Hyper-Production of Pullulan by a Novel Fungus of Aureobasidium melanogenum ZH27 through Batch Fermentation  

Pullulan, which is a microbial exopolysaccharide, has found widespread applications in foods, biomedicines, and cosmetics. Despite its versatility, most wild-type strains tend to yield low levels of pullulan production, and their mutants present genetic instability, achieving a limited increase in pullulan production. Therefore, mining new wild strains with robust pullulan-producing abilities remains an urgent concern. In this study, we found a novel strain, namely, Aureobasidium melanogenum ZH27, that had a remarkable pullulan-producing capacity and optimized its cultivation conditions using the one-factor-at-a-time method. To elucidate the reasons that drove the hyper-production of pullulan, we scrutinized changes in cell morphology and gene expressions. The results reveal that strain ZH27 achieved 115.4 ± 1.82 g/L pullulan with a productivity of 0.87 g/L/h during batch fermentation within 132 h under the optimized condition (OC). This pullulan titer increased by 105% compared with the initial condition (IC). Intriguingly, under the OC, swollen cells featuring 1–2 large vacuoles predominated during a rapid pullulan accumulation, while these swollen cells with one large vacuole and several smaller ones were prevalent under the IC. Moreover, the expressions of genes associated with pullulan accumulation and by-product synthesis were almost all upregulated. These findings suggest that swollen cells and large vacuoles may play pivotal roles in the high level of pullulan production, and the accumulation of by-products also potentially contributes to pullulan synthesis. This study provides a novel and promising candidate for industrial pullulan production.

References:

[1] WANG Q Q, LIN J, ZHOU Q Z, et al. Hyper-Production of Pullulan by a Novel Fungus of Aureobasidium melanogenum ZH27 through Batch Fermentation[J]. International Journal of Molecular Sciences, 2023. DOI:10.3390/ijms25010319.