Bioproduction and applications of aldobionic acids with a focus on maltobionic and cellobionic acid.

Aldobionic acids are sugar acids which consist of a disaccharide with an anomeric acid group. The most famous is lactobionic acid (LBA). LBA is used in many applications such as food and beverages, pharmaceuticals and medicine, cosmetics or chemical processes. During the last decade, all these industries are observing a shift of consumer preferences towards plant-based options. Thus, the biotechnological industry is trying to replace the animal-derived LBA. Maltobionic acid (MBA) and cellobionic acid (CBA) are two stereoisomers of LBA which have emerged as vegan alternatives. However, MBA and CBA face different obstacles related to their industrial production. While traditionally used electrochemical or chemical catalysis often rely on cost intensive and/or hazardous catalysts, novel production methods with microorganisms are still poorly studied. In the first part, this paper discusses both alternatives in terms of their characteristics and applications. In the second part, it reviews the long-studied chemical production and the novel bioproduction methods, which are based on enzymatic and microbial systems. This review concludes with a discussion of future work needed to bring their production to the industrial scale.

Continuous conversion of CO2/H2 with Clostridium aceticum in biofilm reactors.

A lab-scale stirred-tank bioreactor was reversibly retrofitted to a packed-bed and a trickle-bed biofilm reactor to study and compare the conversion of CO2/H2 with immobilised Clostridiumaceticum. The biofilm reactors were characterised and their functionality confirmed. Up to 8.6 g of C. aceticum were immobilised onto 300 g sintered ceramic carrier material, proving biofilm formation to be a robust means for cell retention of C. aceticum. Continuous CO2/H2-fermentation studies were performed with both biofilm reactor configurations as function of dilution rates, partial gas pressures and gas flow rates. The experiments showed that in the packed-bed biofilm reactor, the acetate space-time yield was independent of the dilution rate, because of low H2 gas-liquid mass transfer rates (≤17 mmol H2 L-1 h-1). The continuous operation of the trickle-bed biofilm reactor increased the gas-liquid mass transfer rates to up to 56 mmol H2 L-1 h-1. Consequently, the acetate space-time yield of up to 14 mmol acetate L-1 h-1 was improved 3-fold at hydrogen conversions of up to 96%.