In recent years, various applications for algae-based ß-1,3-glucans have been postulated, including animal feed and human nutrition. Chrysolaminarin is a ß-1,3–1,6-glucan produced by diatoms such as Phaeodactylum tricornutum for energy storage. It is accumulated under nutrient-depleted cultivation conditions. In this study, the production of chrysolaminarin in artificially illuminated scalable flat panel airlift photobioreactors (FPA) was investigated by using P. tricornutum in a two-stage production process. In the growth stage primarily biomass is produced, and the subsequent nitrogen-depleted stage induces the accumulation of chrysolaminarin. Three P. tricornutum strains (SAG 1090-1a, SAG 1090-1b, SAG 1090–6) were cultured at laboratory scale in 6 L-FPA reactors under controlled light conditions to characterize the process and identify a production strain. The chrysolaminarin content of the algae strains was analysed and additionally their contents of eicosapentaenoic acid and fucoxanthin, both of which could be involved in a possible co-production. Strain SAG 1090-1b exhibited the highest biomass productivity and chrysolaminarin content (317 ± 9 mg gDW−1) after nitrogen depletion, and thus stood out as the most suitable for chrysolaminarin production in a two-stage process. A co-production of the three compounds is possible. However, during nitrogen depletion there occurred trade-offs between the compounds. As chrysolaminarin was produced, the amount of fucoxanthin in the culture stagnated or even decreased depending on the selected strain.

Introduction: The Bouguer-Lambert-Beer law is widely used as the fundamental equation for quantification in absorption spectroscopy. However, deviations from the Bouguer-Lambert-Beer law have also been observed, such as chemical deviation and light scattering effect. While it has been proven and shown that the Bouguer-Lambert-Beer law is valid only under very restricted limitations, there are only a few alternatives of analytical models to this law. Based on the observation in the experiments, we propose a novel model to solve the problem of chemical deviation and light scattering effect.Methods: To test the proposed model, a systematic verification was conducted using potassium dichromate solutions and two types of microalgae suspensions with varying concentrations and path lengths.Results: Our proposed model demonstrated excellent performance, with a correlation coefficient (R2) exceeding 0.995 for all tested materials, significantly surpassing the Bouguer-Lambert-Beer law, which had an R2 as low as 0.94. Our results confirm that the absorbance of pure pigment solutions follows the Bouguer-Lambert-Beer law, while the microalgae suspensions do not due to the light scattering effect. We also show that this scattering effect leads to huge deviations for the commonly used linear scaling of the spectra, and we provide a better solution based on the proposed model.Discussion: This work provides a powerful tool for chemical analysis and especially for the quantification of microorganisms, such as the concentration of biomass or intracellular biomolecules. Not only the high accuracy but also the simplicity of the model makes it a practical alternative to the existing Bouguer-Lambert-Beer law.