Browsing by Subject "Mikroalgen"

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Identification and quantification of tocomonoenol isomers in plants and microalgae and investigation of their metabolism in liver cells
(2022) Montoya Arroyo, Alexander; Frank, Jan
Tocopherols (T), tocomonoenols (T1), and tocotrienols (T3) are tocochromanols, a group of bioactive compounds composed of a chromanol ring and a 16-carbon sidechain with biological functions, such as the protection of lipid membranes from oxidation and the modulation of cellular signaling. T have saturated sidechains, while T1 and T3 have a single or three double bonds in theirs, respectively. The prefixes alpha-, beta-, gamma-, and delta- are assigned based on the number and positions of methyl groups on the chromanol ring. alpha-, beta-, gamma-, and delta-congeners of T1 have been reported, with alpha-T1 being the predominantly identified congener. Two different alpha-T1 isomers are known, 11-alpha-T1, which has been mainly found in land plants, and 12-alpha-T1, which has been mostly detected in marine organisms. However, little is known regarding the occurrence of T1 in photosynthetic organisms and their metabolism in the liver, a strong determinant of bioavailability and bioactivity. The aim of this thesis was to evaluate underutilized plant-based food sources, cyanobacteria, and microalgae as potential sources of T1 and to characterize the uptake and conversion into metabolites of T1 in cultured liver cells in comparison to T and T3. Acrocomia aculeata fruits were analyzed for alpha-T1 due to its phylogenetic relationship with Elaeis spp, the most common source of this congener. No alpha-T1 was detected in oils from endosperm and mesocarp of wild fruits of Acrocomia aculeata from Costa Rica. Aerial parts of the local underutilized leafy vegetable Urtica leptophylla were evaluated as source of T1 due to its agronomical potential and previous reports of T1 in leaves of plants. LC-MS analyses indicated that leaves and flowers of Costa Rican Urtica leptophylla contain minor amounts of alpha-T1 and gamma-T1. Cyanobacteria and microalgae from different species and origins were analyzed as source of alpha-T1 due to their role as primary producers in aquatic ecosystems and the reported presence of 12-alpha-T1 in marine phytoplankton. alpha-T1 in cyanobacteria and microalgae ranged from traces up to 17% of the total tocochromanol content. alpha-T1 concentrations alone were higher than the sum of all four T3. 11-alpha-T1 was the major alpha-T1 isomer in cyanobacteria and microalgae, as determined by GC-MS. Hence, 11-alpha-T1 is a product of biosynthetic pathways even in aquatic organisms. The effect of nitrogen depletion during the cultivation of microalgae on their alpha-T1 content was investigated. Nitrogen depletion did neither significantly affect the relative or absolute content of alpha-T1, despite an increase in tocochromanol content, nor the proportion of 11-alpha-T1/12-alpha-T1 in microalgae. The uptake and conversion into metabolites of 11-alpha-T1 in HepG2 liver cells was compared to those of alpha-T3 and alpha-T. Cellular uptake of alpha-T1 in liver cells was higher than that of alpha-T. 11-alpha-T1, similar to alpha-T, was converted mostly to alpha-carboxymethylhydroxychroman in a time dependent manner, but to lower extend than alpha-T3. The effect of both ring methylation and sidechain saturation on the uptake and metabolism of the alpha- and gamma-congeners of T1, T and T3 was studied in HepG2 cells. gamma-Congeners were metabolized at higher extent than alpha-congeners and metabolite production increased with increasing number of double bonds in the sidechain independently of chromanol ring methylation. In conclusion, alpha-T1 is present with up to 17% of total tocochromanols in cultured microalgae, which thus are an important new source of this congener. gamma-T1 is only a minor tocochromanol in U. leptophylla flowers. 11-alpha-T1, and not 12-alpha-T1, is the major alpha-T1 isomer in cyanobacteria and microalgae and nitrogen depletion of microalgae does not significantly affect alpha-T1 concentration. The metabolic conversion of alpha-T1 into alpha-carboxymethylhydroxychroman in HepG2 cells is similar to that of alpha-T and significantly lower than that of alpha-T3, suggesting that it may be handled by the organism similar to alpha-T. In conclusion, novel potential food sources of alpha-T1 have been identified and, because of similarities with alpha-T, its pharmacokinetics and biological activities warrant further investigation.
Investigations on nutritional characteristics of microalgae with emphasis on ruminants
(2019) Wild, Katharina Judith; Rodehutscord, Markus
The main objective of the present thesis was to systematically determine nutritional characteristics of microalgae and evaluate the suitability of microalgae as feedstuffs, particularly for ruminants. The experiments comprised a comprehensive characterisation of microalgae nutrient profiles with chemical-analytical methods and the determination of extent and dynamics of nutrient utilization using in vitro methods. In order to generate a comprehensive database on nutrient composition of microalgae, 16 commercial microalgae biomasses of four genera (Arthrospira, Chlorella, Nannochloropsis, and Phaeodactylum) were analysed utilizing established methods for food and feed evaluation (Manuscript 1). These investigations included determination of the in vitro crude protein (CP) digestibility for pigs. Nutrient analyses showed a considerable variation particularly in concentrations of proximate nutrients, minerals, and fatty acids, both among and within genera. This variation presumably resulted from varying cultivation conditions and it was concluded that general mean values are not appropriate to characterize microalgae in terms nutrient composition. Manuscript 2 aimed to determine characteristics of the nutritional value of microalgae for ruminants utilizing different in vitro methods. The commercial biomasses included in Manuscript 1 were investigated using the Hohenheim Gas Test method. The investigations comprised the determination of several ruminal fermentation characteristics, of the energy value, and of the protein value. A three-step enzymatic in vitro system was used to estimate intestinal digestibility of ruminally undegraded CP (IDP). Ruminal fermentation of the investigated microalgae biomasses was overall low, which was indicated by an overall low level of production of gas and volatile fatty acids, and a low ruminal CP degradation. As a result of low ruminal fermentation, microalgae biomasses were characterized by high concentrations of ruminally undegradable CP (RUP; 386, 399, 315, and 263 g RUP/kg DM at passage rate of 8 %/h for Arthrospira, Chlorella, Nannochloropsis, and Phaeodactylum, respectively). Thus, microalgae appear to be potential alternative protein sources for high performing animals. However, this was contradicted by low IDP, which was determined for microalgae in the present thesis for the first time (mean values for Arthrospira, Chlorella, Nannochloropsis, and Phaeodactylum were 27, 43, 43, and 40 % of RUP respectively). The variation observed in nutrient profiles was reflected in several nutritional characteristics. A common objective of Manuscript 1 and Manuscript 2 was to investigate whether cell disruption affects nutritional characteristics of microalgae. In Manuscript 1, effects of cell disruption on in vitro CP digestibility for pigs were investigated and in Manuscript 2 several in vitro methods were utilized to investigate effects of cell disruption on the nutritional value of microalgae for ruminants. Mechanical cell disruption with a ball mill enhanced in vitro CP digestibility and ruminal fermentation in most of the samples, presumably by the destruction of cells and hence an increase in nutrient accessibility. Nevertheless, concerning the protein value of microalgae in ruminants, application of mechanical cell disruption cannot not be recommended because it decreased RUP but did not increase IDP so that intestinal digestible RUP was overall decreased by cell disruption. The aim of the third manuscript was to investigate the effects of variable cultivation conditions on nutrient composition and nutritional characteristics for ruminants of the microalgae Chlorella vulgaris. Chlorella vulgaris was cultivated under varying conditions (saturation, nitrogen and CO2 depletion, outdoor cultivation). The obtained biomasses were analysed for their nutrient composition and their nutritional value for ruminants using different in vitro methods. Both, nutrient composition and characteristics of the nutritional value for ruminants were affected by the cultivation process. Nutrient deficient conditions had rather adverse effects in terms of digestibility, protein value, and nutrient productivity. It can be concluded that microalgae have potential as alternative protein source for ruminants. Nevertheless, this potential is contradicted by low IDP, but the findings obtained herein have to be verified in future studies. Furthermore, the results of the present thesis show that nutrient composition and ruminal fermentation characteristics of microalgae vary considerably between and in many cases even within microalgae genera. Thus, to the extent possible, it should be strived for a standardisation of cultivation conditions, in order allow better predictions of nutritional characteristics of microalgae.
Die Mikroalge Phaeodactylum tricornutum : Bioverfügbarkeit, Sicherheit und potenzieller gesundheitlicher Nutzen für die humane Ernährung
(2023) Kopp, Lena Janine; Bischoff, Stephan C.
The dissertation by Lena Kopp investigated the suitability of the microalga Phaeodactylum tricornutum (PT) for human nutrition. PT contains essential nutrients such as the long-chain omega-3 fatty acid eicosapentaenoic acid (EPA), which is otherwise found mainly in fish. In addition, PT contains a high content of other nutrients such as proteins, carotenoids (in particular fucoxanthin), vitamins and β-glucans, which have nutritive and therapeutic potential. Clinical and animal studies have shown that the PT biomass ingestion is safe and has potential health effects, such as anti-inflammatory and prebiotic effects. The results suggest that PT can be used as a food for human nutrition with possible health-promoting effects.
Operating strategy to reduce the energy consumption of flat-panel airlift photobioreactors with respect to mixing of thermosynechococcus elongatus suspension cultures : light-specific adaptation of the superficial gas velocity
(2018) Bergmann, Peter; Trösch, Walter
Photoautotrophic microalgae mass production is limited by light availability due to effects of absorption and reflection, especially throughout outdoor cultivation prohibiting the adjustment of photon-flux density (PFD). Generating turbulence within the cultures in order to minimize photolimiting and photoinhibitive effects is the method of choice to overcome that obstacle. Then again, energy required for its generation represents one of the major drivers contributing to overall production costs of microalgae biotechnology. The present work describes the development of an advanced operating strategy for the mixing of flat-panel airlift loop photobioreactors (FPA-PBRs) that through its application decreases the specific energy consumption, thus the energy requirement per unit of biomass produced, when cultivating phototrophic microorganisms. Experiments were carried out with the thermophilic cyanobacterium Thermosynechococcus elongatus BP-1 utilizing distinct FPA-PBRs equipped with culture-flow directing installations and illuminated by high pressure sodium (HPS) lamps. In the first paper, the impact of utilizing respective FPA-PBRs is investigated. Preliminary experiments were performed in order to eliminate any limitations beyond the sphere of influence of photobioreactor (PBR) design. Apart from the NO3- concentration which had to be retained at 2000 mg L-1 to sustain non-limited growth, special attention was paid to the administration of dissolved inorganic carbon (DIC), inter alia in the form of hydrogen carbonate as CO2 gas solubility was limited by the applied cultivation temperature of 55°C. It is for this reason, in conjunction with a short residence time of the CO2-enriched air bubbles that an increase in CO2 concentration showed only minor effects compared to increasing carbonate concentration that directly correlated to maximum productivity attaining 2.9 gDW L-1 d-1, the highest to be reported for T. elongatus BP-1, using 0.04 g L-1 Na2CO3. When comparing PBRs with and without culture flow directing installations, e.g. static mixers, it was found that the former outperformed the latter as an increase in maximum volumetric productivity and final biomass concentration by a factor of 3.4 and 2.0 was recorded, respectively, whilst the energy input in the form of superficial gas velocity remained unchanged. The enhanced growth performance was attributed to improved specific light availability due to the formation of eddies within cultures induced by static mixers. Thereby, light dependent downregulation of quantum-yield and respiratory losses were reduced, ultimately allowing for a more efficient photon-utilization towards assimilatory photochemistry when compared to randomly mixed cultures. In the second study, the joined impact of PFD, biomass concentration and superficial gas velocity is investigated and an operating strategy for FPA-PBRs deduced. Preliminary experiments were performed in order to establish a modified photosynthesis irradiance (PI) curve at default mixing settings which defined the light compensation point and the irradiance of saturation with 100 μmol m-2 s-1 and 400 μmol m-2 s-1, respectively. Cultivations were then performed at sub-, quasi-, and supra-saturating PFDs (180 .. 780 μmol m-2 s-1) utilizing multiple gas flow velocities (0.11 .. 0.83 vvm). It was found that at a given velocity, productivity and final biomass concentration increased with increasing PFD. Moreover, it was found that in comparison with default mixing settings, the superficial gas velocity during sub-saturating PFD and/or biomass concentrations < 3 gDW L-1 can be reduced to cut operational expenditures (OPEX) on mixing, whilst an increase during supra-saturating PFD and/or higher biomass concentrations enhances productivity and final biomass yield. An operating strategy based on the PFD-triggered adjustment of the superficial gas velocity is proposed and results were mathematically translated to exemplary outdoor diurnal cycles of PFD. By applying the strategy on sunny days, productivity is increased by 24%, while reducing not only energy input but also CO2-demand by 11%. On cloudy days, productivity is only slightly increased but energy input and CO2-demand reduced by 37%. Consequently, the specific energy requirement of FPA-PBRs when cultivating phototrophic microorganisms is reduced significantly, especially at locations with only stochastic light supply, e.g. in temperate latitudes.