Browsing by Author "Ebbing, Tobias"

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    Beta-glucan production of Phaeodactylum tricornutum, Monodopsis subterranea and Cylindrotheca fusiformis during nitrogen depletion
    (2023) Frick, Konstantin; Ebbing, Tobias; Yeh, Yen-Cheng; Schmid-Staiger, Ulrike; Tovar, Günter E. M.
    AbstractBeta-glucans are polysaccharides that can be used for different applications, for example as an immunomodulator in food or feed or for managing high cholesterol levels. Certain microalgae species use beta-glucans as energy storage, accumulating them during nutrient depletion. In this study, we examined and compared beta-glucan production during nitrogen depletion in three different algae species, Phaeodactylum tricornutum, Monodopsis subterranea and Cylindrotheca fusiformis, grown in artificially illuminated flat panel airlift reactors, in order to determine the most promising microalgae species for beta-glucan production. Co-products such as fatty acids (especially eicosapentaenoic acid) and the carotenoid fucoxanthin (not produced by M. subterranea) were also considered. Biomass analysis showed that P. tricornutum cultures reached a maximal beta-glucan content of 317 ± 9 mg gDW-1, M. subterranea cultures reached 188 ± 6 mg gDW-1 and C. fusiformis cultures reached 129 ± 13 mg gDW-1. Furthermore, beta-glucan production was faster in P. tricornutum cultures. However, the maximum volumetric beta-glucan concentration reached was higher in M. subterranea cultures compared to P. tricornutum cultures as M. subterranea cultures produced more biomass during nitrogen depletion. In terms of possible co-products, P. tricornutum produced fucoxanthin and EPA, whereas M. subterranea did not produce fucoxanthin. However, M. subterranea exhibited a higher EPA content, which remained above 45 mg g-1 even after several days of nitrogen depletion. Overall, our results suggest that P. tricornutum and M. subterranea are both suitable species for beta-glucan production in flat panel airlift reactors.
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    Improving determination of pigment contents in microalgae suspension with absorption spectroscopy : light scattering effect and Bouguer-Lambert-Beer law
    (2023) Yeh, Yen-Cheng; Ebbing, Tobias; Frick, Konstantin; Schmid-Staiger, Ulrike; Haasdonk, Bernard; Tovar, Günter E. M.
    The Bouguer-Lambert-Beer (BLB) law serves as the fundamental basis for the spectrophotometric determination of pigment content in microalgae. Although it has been observed that the applicability of the BLB law is compromised by the light scattering effect in microalgae suspensions, in-depth research concerning the relationship between the light scattering effect and the accuracy of spectrophotometric pigment determination remains scarce. We hypothesized that (1) the precision of spectrophotometric pigment content determination using the BLB law would diminish with increasing nonlinearity of absorbance, and (2) employing the modified version of the BLB (mBLB) law would yield superior performance. To assess our hypotheses, we cultivated Phaeodactylum tricornutum under varying illumination conditions and nitrogen supplies in controlled indoor experiments, resulting in suspensions with diverse pigment contents. Subsequently, P. tricornutum samples were diluted into subsamples, and spectral measurements were conducted using different combinations of biomass concentrations and path lengths. This was carried out to assess the applicability of the BLB law and the nonlinearity of absorbance. The chlorophyll a and fucoxanthin contents in the samples were analyzed via high-performance liquid chromatography (HPLC) and subsequently used in our modeling. Our findings confirm our hypotheses, showing that the modified BLB law outperforms the original BLB law in terms of the normalized root mean square error (NRMSE): 6.3% for chlorophyll a and 5.8% for fucoxanthin, compared to 8.5% and 7.9%, respectively.
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    Influence of light conditions on the production of chrysolaminarin using Phaeodactylum tricornutum in artificially illuminated photobioreactors
    (2023) Frick, Konstantin; Ebbing, Tobias; Yeh, Yen‐Cheng; Schmid‐Staiger, Ulrike; Tovar, Günter E. M.
    The light conditions are of utmost importance in any microalgae production process especially involving artificial illumination. This also applies to a chrysolaminarin (soluble 1,3-β-glucan) production process using the diatom Phaeodactylum tricornutum. Here we examine the influence of the amount of light per gram biomass (specific light availability) and the influence of two different biomass densities (at the same amount of light per gram biomass) on the accumulation of the storage product chrysolaminarin during nitrogen depletion in artificially illuminated flat-panel airlift photobioreactors. Besides chrysolaminarin, other compounds (fucoxanthin, fatty acids used for energy storage [C16 fatty acids], and eicosapentaenoic acid) are regarded as well. Our results show that the time course of C-allocation between chrysolaminarin and fatty acids, serving as storage compounds, is influenced by specific light availability and cell concentration. Furthermore, our findings demonstrate that with increasing specific light availability, the maximal chrysolaminarin content increases. However, this effect is limited. Beyond a certain specific light availability (here: 5 µmolphotons gDW-1 s-1) the maximal chrysolaminarin content no longer increases, but the rate of increase becomes faster. Furthermore, the conversion of light to chrysolaminarin is best at the beginning of nitrogen depletion. Additionally, our results show that a high biomass concentration has a negative effect on the maximal chrysolaminarin content, most likely due to the occurring self-shading effects.