Uncover aldehydes in biomass hydrolyzates: disproportionation of aldehydes in alkaline solution and subsequent measurement using an automated HPAEC-PAD method.

High-performance anion exchange chromatography coupled to pulsed amperometric detection (HPAEC-PAD) was used for developing a method for identifying and quantifying aldehydes in biomass hydrolyzates. This method was optimized to the requirements of HPAEC-PAD in order to allow for a simultaneous determination of aldehydes by respective Cannizzaro alcohols. To this end, sodium hydroxide concentration (0.1 to 5.0 mol/L), temperature (30 to 40 °C), and reaction time (0 to 24 h) were investigated for sufficient and reproducible disproportionation of the biomass-derived aldehydes. The optimized method for aldehyde disproportionation and subsequent measurement are 1 mol/L sodium hydroxide, 40 °C, and 1 h reaction time. The detection limits resulting from this method are lower than 68.55 mg/L and the sensitivity above 0.024 (nC min)/(mg/L) for 3,4-dimethoxybenzaldehyde. Linearity for aldehyde calibration always exceeded 0.98. Thus, HPAEC-PAD analysis allows for the quantification of biomass-derived compounds from all natural polymers and, therefore, it has exemplarily been used to quantify aldehyde concentration of beech wood, orange peel, and algae biomass hydrolyzates. Graphical abstract.

Investigation of poly(γ-glutamic acid) production via online determination of viscosity and oxygen transfer rate in shake flasks.

BACKGROUND: Poly(γ-glutamic acid) (γ-PGA) is a biopolymer with many useful properties making it applicable for instance in food and skin care industries, in wastewater treatment, in biodegradable plastics or in the pharmaceutical industry. γ-PGA is usually produced microbially by different Bacillus spp. The produced γ-PGA increases the viscosity of the fermentation broth. In case of shake flask fermentations, this results in an increase of the volumetric power input. The power input in shake flasks can be determined by measuring the torque of an orbitally rotating lab shaker. The online measurement of the volumetric power input enables to continuously monitor the formation or degradation of viscous products like γ-PGA. Combined with the online measurement of the oxygen transfer rate (OTR), the respiration activity of the organisms can be observed at the same time. RESULTS: Two different Bacillus licheniformis strains and three medium compositions were investigated using online volumetric power input and OTR measurements as well as thorough offline analysis. The online volumetric power input measurement clearly depicted changes in γ-PGA formation due to different medium compositions as well as differences in the production behavior of the two investigated strains. A higher citric acid concentration and the addition of trace elements to the standard medium showed a positive influence on γ-PGA production. The online power input signal was used to derive an online viscosity signal which was validated with offline determined viscosity values. The online measurement of the OTR proved to be a valuable tool to follow the respiration activity of the cultivated strains and to determine its reproducibility under different cultivation conditions. CONCLUSIONS: The combination of the volumetric power input and the OTR allows for an easy and reliable investigation of new strains, cultivation conditions and medium compositions for their potential in γ-PGA production. The power input signal and the derived online viscosity directly reflect changes in γ-PGA molecular weight and concentration, respectively, due to different cultivation conditions or production strains.