Pullulan Production from Lignocellulosic Plant Biomass or Starch-Containing Processing Coproduct Hydrolysates

Abstract

The complex polysaccharide pullulan is characterized as a glucose-containing biopolymer that is both water-soluble and neutral in polarity. A variety of commercial applications exist for pullulan, including its utilization as a flocculant, a blood plasma substitute, a food additive, a dielectric material, an adhesive, or a packaging film. The fungus Aureobasidium pullulans has used several hydrolysates derived from plant biomass or starch-containing processing coproducts to support polysaccharide production. These include various plant biomass or processing coproduct streams such as lignocellulosic-containing peat, prairie grass, stalks, hulls, straw, shells, and pods or starch-containing coproducts from the processing of corn, rice, jackfruit seeds, palm kernels, cassava, and potatoes. The pullulan concentration produced by A. pullulans and the pullulan content of the polysaccharide depend on the plant hydrolysate carbon content and the strain used. If a lower-cost culture medium for fungal pullulan production were to be developed, a more economical approach to synthesizing commercial pullulan would be the utilization of plant-derived hydrolysates. This review examines the ability of selected hydrolysates of lignocellulosic plant biomass or plant-derived starch-containing processing coproducts to support A. pullulans polysaccharide synthesis in order to identify those substrates with the greatest potential for reducing the cost of commercial pullulan.

Introduction

The extracellular complex polysaccharide pullulan is synthesized by the imperfect fungus Aureobasidium pullulans, characterized as a black yeast [1]. The synthesis of pullulans is not observed for all species classified within the genus Aureobasidium [2]. Instead, only certain strains of A. pullulans have been shown to be capable of synthesizing pullulan [2]. Pullulan is characterized as a water-soluble neutral biopolymer that can be precipitated by the addition of alcohol for gravimetric determinations [3].

The structure of pullulan (Figure 1) is a complex linear polysaccharide composed of maltotriose units linked through α-D-(1→6) bonds on its terminal glucose residues [4,5,6,7]. Depending on the A. pullulans strain chosen, as well as the selected growth conditions, the molecular weight of pullulan has been found to vary from 50,000 to 2,500,000 daltons, providing a range of pullulan biopolymers that could be used for different commercial applications [4]. A pullulan-degrading activity has been detected in A. pullulans ATCC 42023 that likely affects the molecular weight of the polysaccharide after its activity appears after 120 h of fermentation [5].

In this review, the production of pullulan relative to growth conditions, as well as the existing commercial applications for pullulan as a polysaccharide gum, were explored. Subsequently, the ability of lignocellulosic plant biomass hydrolysates to be used to support pullulan production by A. pullulans cells was investigated. Lastly, hydrolysates of starch-containing plant biomass processing coproducts were studied as possible substrates to sustain pullulan production by A. pullulans. Studying these plant biomass hydrolysates should help identify which hydrolysates could make the production of pullulan more economical from a feedstock perspective.

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West, T.P. Pullulan Production from Lignocellulosic Plant Biomass or Starch-Containing Processing Coproduct Hydrolysates. Fermentation 2026, 12, 84. https://doi.org/10.3390/fermentation12020084

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