Food Microalgae Research Articles

Effect mechanism of metal cations on the interface interaction of cell-collector-bubble for microalgal foam flotation

Foam flotation is generally recognized as a low-cost and efficient technology for the harvesting of microalgae for food, feed and fuel production, as well as environmental remediation. However, the harvesting efficiency of microalgae using foam flotation is restricted by the residual metal cations in the medium, and the corresponding inhibition mechanism has not yet been revealed. This study investigated the effects of metal cations in the medium on the harvesting efficiency and concentration factor during the foam flotation of Scenedesmus acuminatus. The interface interaction of cell-collector-bubble effected by metal cations was revealed by quantifying the amount of collector (cetyl trimethylammonium bromide, CTAB) between cells and bubbles, as well as the response of bubble interface characteristics. Results showed that the harvesting efficiency dropped linearly as the increase of cationic concentrations. Under the CTAB dose of 20 mg L−1, the harvesting efficiency decreased from 98.65% to 56.77% with a decrease of concentration factor from 25.41 to 9.05 in the presence of metal cations. The Na+ and Mg2+ in the medium were the major inhibitors. The inhibitory mechanisms revealed that metal cations obviously impeded the adsorption of CTAB onto the cells by competing adsorption site, resulting in a low harvesting efficiency. The presence of metal cations also inhibited the bubble coalescence and slowed down drainage velocity in the plateau channel of foam layer, forming foam with higher water content, thus reducing the concentration factor. A schematic illustration is proposed to better understand the effect mechanism of metal cations on microalgal foam flotation. This study might facilitate the process development in an effort to overcome the inhibition of cations during microalgal foam flotation.

Bioactive peptides from microalgae: Focus on anti-cancer and immunomodulating activity.

In addition to the rapidly expanding field of using microalgae for food and feed, microalgae represent a tremendous potential for new bioactive compounds with health-promoting effects. One field where new therapeutics is needed is cancer therapy. As cancer therapy often cause severe side effects and loose effect due to development of drug resistance, new therapeutic agents are needed. Treating cancer by modulating the immune response using peptides has led to unprecedented responses in patients. In this review, we want to elucidate the potential for microalgae as a source of new peptides for possible use in cancer management. Among the limited studies on anti-cancer effects of peptides, positive results were found in a total of six different forms of cancer. The majority of studies have been performed with different strains of Chlorella, but effects have also been found using peptides from other species. This is also the case for peptides with immunomodulating effects and peptides with other health-promoting effects (e.g., role in cardiovascular diseases). However, the active peptide sequence has been determined in only half of the studies. In many cases, the microalga strain and the cultivation conditions used for producing the algae have not been reported. The low number of species that have been explored, as opposed to the large number of species available, is a clear indication that the potential for new discoveries is large. Additionally, the availability and cost-effectiveness of microalgae make them attractive in the search for bioactive peptides to prevent cancer.

Techno-economic assessment of microalgae cultivation in a tubular photobioreactor for food in a humid continental climate

Fish as the primary source for the essential n − 3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) cannot cover the global demand for these important nutrients resulting in a supply gap of currently 1.1 million tons of EPA + DHA annually. A further exploitation of natural fish stocks is linked to great damage to ecosystems. Oleaginous microalgae are a natural source for EPA and DHA and could possibly contribute to closing this gap. The cultivation in photobioreactors (PBR) in a ‘cold-weather’ climate showed that microalgae compare favorably to aquaculture fish. The present study assesses the economic potential of microalgae for food in such system model. Techno-economic assessment was conducted on the basis of a dynamic system model for the cultivation of Nannochloropsis sp. in industrial scale in Central Germany over a time span of 30 years. The net present value (NPV) and return-on-investment (ROI) were obtained for a number of scenarios in which technic and economic parameters were altered. Taking the size of the PBR considered into account, the cultivation of Nannochloropsis sp. yielded a positive NPV of EUR 4.5 million after 30 years which translates to an annualized ROI of 1.87%. The sensitivity analysis overall resulted in annualized ROIs between 1.12 and 2.47%. Major expenditures comprised the PBR infrastructure, maintenance and labor cost. An extended cultivation season by four weeks was responsible for an NPV surplus of almost one third (32%). An increase in the selling price by 15% was responsible for a 47% higher NPV. In comparison with Atlantic salmon (Salmo salar) raised in aquaculture, EPA from Nannochloropsis sp. resulted in about halved cultivation costs (− 44 to − 60%). In this study we could show that microalgae from photoautotrophic cultivation not only have the potential to supply humans with essential nutrients, but they are also a lucrative investment, even in a ‘cold-weather’ climate where cultivation cannot take place year round.Graphic abstract

Harvesting Microalgae for Food and Energy Products

AbstractMicroalgae are promising biological factories for diverse natural products. Microalgae tout high productivity, and their biomass has value in industrial products ranging from biofuels, feedstocks, food additives, cosmetics, pharmaceuticals, and as alternatives to synthetic or animal‐derived products. However, harvesting microalgae to extract bioproducts is challenging given their small size and suspension in liquid growth media. In response, technologic developments have relied upon mechanical, chemical, thermal, and biological means to dewater microalgal suspensions and further extract bioproducts. In this review, the effectiveness and considerations were evaluated for the implementation of microalgae harvesting techniques. Nonbiological methods—filtration, chemical, electrical, and magnetic nanoparticle flocculation, centrifugation, hydrothermal liquefaction, and solvent‐based extraction, as well as biological coculture‐based methods are included. Recent advances in coculture algae‐flocculation technologies that involve bacteria and fungi are summarized. These produce a variety of natural bioproducts, which show promise in fuel and food additive applications. Furthermore, this review addresses the developments of genetic tools and resources to optimize the productivity and harvesting of microalgae or to provide new bioproducts via heterologous expression. Finally, a glimpse of future biotechnologies that will converge to produce, harvest, and process microalgae using sustainable and cost‐effective methods is offered.

Electroporation as a Solvent-Free Green Technique for Non-Destructive Extraction of Proteins and Lipids From Chlorella vulgaris.

Proteins extracted from microalgae for food, personal care products and cosmetics must be of high purity, requiring solvent-free extraction techniques despite their generally considerably lower protein yield and higher energy consumption. Here, three such approaches for green extraction of proteins from Chlorella vulgaris were evaluated: ultrasound, freeze-thawing, and electroporation; chemical lysis was used as positive control (maximal achievable extraction), and no extraction treatment as negative control. Compared to chemical lysis, electroporation yielded the highest fraction of extracted protein mass in the supernatant (≤27%), ultrasound ≤24%, and freeze-thawing ≤15%. After a growth lag of several days, electroporated groups of algal cells started to exhibit growth dynamics similar to the negative control group, while no growth regeneration was detected in groups exposed to ultrasound, freeze-thawing, or chemical lysis. For electroporation as the most efficient and the only non-destructive among the considered solvent-free protein extraction techniques, simultaneous extraction of intracellular algal lipids into supernatant was then investigated by HPLC, proving relatively low-yield (≤7% of the total algal lipid mass), yet feasible for glycerides (tri-, di-, and mono-) as well as other fatty acid derivatives. Our results show that electroporation, though lower in extraction yields than chemical lysis or mechanical disintegration, is in contrast to them a technique for largely debris-free extraction of proteins from microalgae, with no need for prior concentration or drying, with feasible growth regeneration, and with potential for simultaneous extraction of intracellular algal lipids into the supernatant.

Nuances of microalgal technology in food and nutraceuticals: a review

PurposeThe purpose of this paper is to acquaint the readers with the insights regarding the interventions of microalgal technology for production of metabolites and functional ingredients from microalgae for food and nutraceutical application and exploration of microalgae biomass for food application.Design/methodology/approachVarious information databases such as journals, library catalogues and professional websites were used to collect information pertaining to application of microalgae in food and nutraceutical sector. Systematic review was made with recent studies covering the vital aspects of art of microalgae cultivation for metabolite production, functional ingredients from microalgae, market scenario and utilisation of microalgae biomass for the valorisation of the food products. Key points have been discussed after every section to highlight the practical implications to make this review more insightful for the readers.FindingsMicroalgal technology provides sustainable solution for its application in food and nutraceutical sector. The heart of metabolite production lies in the optimisation of cultivation conditions of microalgae. Wide array of functional components are obtained from microalgae. Microalgae offer an alternative source for omega-3 fatty acids. Microalgae is widely exploited for production of pigments, namely, ß-carotene, astaxanthin, lutein, phycocyanin and chlorophyll, that have important implication as natural colourants and nutraceuticals in food. Larger diversity of sterols found in microalgae confers bioactivity. Microalgae is finding its place in market shelves as nutraceuticals where its functional ingredients are in the form of powder, tablets, extract and beverages and in innovative products such as microalgae protein and fat, culinary algae oil and butter. Sprulina and Chlorella are popular choice for the supplementation of food products with microalgae biomass.Originality/valueThis is a comprehensive review that highlights the application of microalgal technology for the development of healthy food products and presents holistic intervention in food and nutraceutical sector.

A novel strategy for isolation and purification of fucoxanthinol and fucoxanthin from the diatom Nitzschia laevis.

In this study, the microalga Nitzschia laevis (N. laevis) can accumulate a marine carotenoid fucoxanthinol. In particular, fucoxanthinol was firstly isolated from microalgae, accompanied by its derivative fucoxanthin. The identification and quantification of fucoxanthinol and fucoxanthin were determined by ultra-performance liquid chromatography coupled to photodiode array detector-quadrupole/travelling-wave ion mobility mass spectrometry/time-of-flight mass spectrometry (UPLC-PDA-TWIMS-QTOF-MS). Furthermore, a cost-effective approach mediated with solid-phase extraction (SPE) and thin-layer chromatography (TLC) technique was used to isolate and purify fucoxanthinol and fucoxanthin from the extracts of N. laevis. This two-step method can obtain 98% fucoxanthinol and 95% fucoxanthin, with the recovery efficiencies of around 85% for fucoxanthinol and 70% for fucoxanthin, respectively. Moreover, 1H and 13C nuclear magnetic resonance (NMR) techniques were adopted to record the purified compounds for supporting the above results. In all, the developed method has a promising potential to purify fucoxanthinol and fucoxanthin of microalgae for food and pharmaceutical applications.

Effect of Suspended Particulate Matter on the Accumulation of Dissolved Diarrhetic Shellfish Toxins by Mussels (Mytilus galloprovincialis) under Laboratory Conditions.

In recent years, detection of trace amounts of dissolved lipophilic phycotoxins in coastal waters has been possible using solid phase adsorption toxin tracking (SPATT) samplers. To explore the contribution of dissolved diarrhetic shellfish toxins (DST) to the accumulation of toxins by cultivated bivalves, mussels (Mytilus galloprovincialis) were exposed to different concentrations of purified okadaic acid (OA) and dinophysistoxin-1 (DTX1) in filtered (0.45 µm) seawater for 96 h. Accumulation and esterification of DST by mussels under different experimental conditions, including with and without the addition of the food microalga Isochrysis galbana, and with the addition of different size-fractions of suspended particulate matter (SPM) (<75 µm, 75–150 µm, 150–250 µm) were compared. Results showed that mussels accumulated similar amounts of OA and DTX1 from seawater with or without food microalgae present, and slightly lower amounts when SPM particles were added. Mussels preferentially accumulated OA over DTX1 in all treatments. The efficiency of the mussel’s accumulation of OA and DTX1 from seawater spiked with low concentrations of toxins was higher than that in seawater with high toxin levels. A large proportion of OA (86–94%) and DTX1 (65–82%) was esterified to DTX3 by mussels in all treatments. The proportion of I. galbana cells cleared by mussels was markedly inhibited by dissolved OA and DTX1 (OA 9.2 µg L−1, DTX1 13.2 µg L−1) in seawater. Distribution of total OA and DTX1 accumulated in the mussel tissues ranked in all treatments as follows: digestive gland > gills > mantle > residual tissues. However, the percentage of total DST in the digestive gland of mussels in filtered seawater (67%) was higher than with the addition of SPM particles (75–150 µm) (51%), whereas the gills showed the opposite trend in filtered seawater with (27%) and without (14.4%) SPM particles. Results presented here will improve our understanding of the mechanisms of DST accumulation by bivalves in marine aquaculture environments.

Enhanced lipid and biomass production by a newly isolated and identified marine microalga.

BackgroundThe increasing demand for microalgae lipids as an alternative to fish has encouraged researchers to explore oleaginous microalgae for food uses. In this context, optimization of growth and lipid production by the marine oleaginous V2-strain-microalgae is of great interest as it contains large amounts of mono-unsaturated (MUFAs) and poly-unsaturated fatty acids (PUFAs).MethodsIn this study, the isolated V2 strain was identified based on 23S rRNA gene. Growth and lipid production conditions were optimized by using the response surface methodology in order to maximize its cell growth and lipid content that was quantified by both flow cytometry and the gravimetric method. The intracellular lipid bodies were detected after staining with Nile red by epifluorescence microscopy. The fatty acid profile of optimal culture conditions was determined by gas chromatography coupled to a flame ionization detector.ResultsThe phenotypic and phylogenetic analyses showed that the strain V2 was affiliated to Tetraselmis genus. The marine microalga is known as an interesting oleaginous species according to its high lipid production and its fatty acid composition. The optimization process showed that maximum cell abundance was achieved under the following conditions: pH: 7, salinity: 30 and photosynthetic light intensity (PAR): 133 μmol photons.m−2.s−1. In addition, the highest lipid content (49 ± 2.1% dry weight) was obtained at pH: 7, salinity: 37.23 and photosynthetic light intensity (PAR): 188 μmol photons.m−2.s−1. The fatty acid profile revealed the presence of 39.2% and 16.1% of total fatty acids of mono-unsaturated fatty acids (MUFAs) and poly-unsaturated fatty acids (PUFAs), respectively. Omega 3 (ω3), omega 6 (ω6) and omega 9 (ω9) represented 5.28%, 8.12% and 32.8% of total fatty acids, respectively.ConclusionsThis study showed the successful optimization of salinity, light intensity and pH for highest growth, lipid production and a good fatty acid composition, making strain V2 highly suitable for food and nutraceutical applications.

Heterotrophic growth and nutrient productivities of Tetraselmis chuii using glucose as a carbon source under different C/N ratios

The genus Tetraselmis includes various species that are widely used as food microalgae in aquaculture. However, the mass cultivation of Tetraselmis spp. has been restricted to traditional photoautotrophic culture. Here, we investigated the heterotrophic culture condition for Tetraselmis chuii and assessed growth rate, morphology, and biomass productivity of T. chuii under heterotrophic culture conditions. Protein, polysaccharide, chlorophyll, total lipids, and fatty acid compositions under different initial C/N ratios were also analyzed. Tetraselmis chuii was found to be able to grow using glucose as the sole carbon source under strict heterotrophic conditions. Moreover, T. chuii showed a better heterotrophic growth status in the medium with 10 g L−1 glucose compared to the autotrophic condition. Comparatively high optical density and biomass were obtained at C/N ratios of 16 and 12. The dry weights of T. chuii under C/N ratios of 16 and 12 were 1.37 ± 0.04 and 1.26 ± 0.06 mg mL−1, respectively, significantly higher than those of the autotrophic group. In addition, T. chuii synthesized more polysaccharide under heterotrophic conditions, especially at a C/N ratio of 24. Tetraselmis chuii cultured under C/N ratios of 4 and 8 produced the highest percentages of C16:0 (43.36 %) and C18:1 (47.49 %) fatty acids, and more fatty acids, including C14:0, C18:0, C20:2, and C20:4, were detected in the groups with C/N ratios of 4 and 24. These findings may provide the basis for the mass culture of heterotrophic T. chuii by highlighting sources of plentiful nutrient substances, especially polysaccharides, for aquaculture.

Cell Membrane Permeabilization Studies of &lt;italic&gt;Chlorella&lt;/italic&gt; sp. by Pulsed Electric Fields

Microalgae cell membrane permeabilization has been studied, for Chlorella sp., in a continuous 6-L prototype for different field strengths in order to minimize the specific energy supplied and the treatment time. Regarding lower electrical field strength values, the optimal results were achieved at 10 kV/cm, 200 Hz, and 5-μs per pulse, corresponding to an energy delivered of 9 kJ/kg of culture, with 97% of cells affected after 300 ms of treatment time. Regarding energy delivered per kilogram of Biomass, the best result was 2.7 MJ/kg of biomass with 95% of cells affected after 300 ms of treatment time and was achieved at 15 kV/cm, 200 Hz, and 5-μs per pulse. Pulsed electric field effect was quantified by flow cytometry using propidium iodide as a viability stain. The influence of conductivity and cell concentration was also analyzed. The final goal was to evaluate the use of this technology in terms of increasing bioaccessibility of bioactive compounds present in microalgae for food and feed purposes. These results, obtained only for chlorophyll a and b, did not show any beneficial effect of this technology against nontreated biomass.

Culturing Chaetoceros muelleri using simplified media with different N sources: effects on production and lipid content

Land-based bivalve aquaculture depends on large-scale cultures of live microalgae for food. The intensity of large-scale microalgal production is important for cost-effectiveness. Using Walne’s medium as the control, simplified media containing nitrogen, phosphorus, silica, iron, manganese and vitamins were designed to determine the impact of nitrogen source and molar N:P ratio (sodium nitrate, NO3 9:1, ammonium chloride, NH4 9:1 and NH4 25:1) on growth, dry-weight biomass, culture longevity and lipid content of Chaetoceros muelleri, a diatom commonly used in shellfish aquaculture. During the exponential phase (day 6), dry-weight production in simplified media was similar to controls, indicating that this microalga can grow successfully on simplified media and use ammonium as the nitrogen source. The cultures grown on nitrate or ammonium differed in their time-course. Low nitrogen concentration in cultures grown with nitrate caused the collapse of these cultures within 11–13 days, after a short stationary phase. Cultures grown with ammonium had a longer stationary phase and were still alive on day 20, in spite of the low nitrogen concentrations observed after day 13 in cultures grown with NH4 9:1. During stationary phase (day 18) there was an increase in lipid content of algae under conditions of low nitrogen availability (NH4 9:1) and extended low phosphorus availability (NH4 25:1). Considering dry weight production, culture longevity, nutrient efficiency and lipid composition, simplified media containing ammonium, phosphorus, silica, iron, manganese and vitamins are a viable and profitable choice for batch culture of C. muelleri. In the exponential phase, the simplified medium NH4 9:1 was as effective as the control. Overall, both of the simplified media using ammonium are effective and suitable, depending on the purpose of the cultures and whether lipid contents (NH4 9:1), dry weight biomass (NH4 25:1) or nitrogen input and output (NH4 9:1) are desired.

Biorefinery of microalgae for food and fuel

Microalgae are a promising source for proteins, lipids and carbohydrates for the food/feed and biofuel industry. In comparison with soya and palm oil, microalgae can be grown in a more efficient and sustainable way. To make microalgae production economically feasible it is necessary to optimally use all produced compounds. To accomplish this focus needs to be put on biorefinery techniques which are mild and effective. Of the techniques described, Pulsed Electric Field (PEF) seems to be the most developed technique compared to other cell disruption applications. For separation technology ionic liquids seems most promising as they are able to both separate hydrophobic and hydrophilic compounds. But additional studies need to be evolved in the coming years to investigate their relevance as novel cell disruption and separation methods. We propose a complete downstream processing flow diagram that is promising in terms of low energy use and state of the art knowledge.

굴, Crassostrea gigas 유생 성장단계별 미세조류 12의 소화도

Twelve species of food microalgae were investigated to clarify the digestion index of Crassostrea gigas larvae using epifluorescence microscopy to choose an appropriate diet for artificial seed production in hatchery. An experiment was conducted using 1 (D shaped stage), 4 (Early umbo stage), 8 (umbo stage) and 12 (Full grown stage) days old larvae. larvae were stocked in 1 L flasks at 5 individuals/mL and fed 10×10 4 algal cells/mL of each species individually. Prior to larvae were fed for 3 h and then were observed under the microscope to detect ingestion; larvae were then sieved and replaced in 1 L flasks containing filtered seawater and were observed after 3, 5 and 8 h to analyse the digestion index. Values of digestion indices were specific for each alga. No evidence for the ingestion of Thalassiosira weissflogii was evident at all larval development stages tested. Digestion indices of others microalgae were 0.8-99.7% at 4 stage of larval development stages: Chlorella ellipsoidea (0.8-5.4%), Nannochloris oculata (1.4-5.0%), Isochrysis galbana (99.1-99.5%), Pavlova lutheri (99.1-99.5%), I. aff. galbana (99.4-99.5%), Cheatoceros calcitrans (0.0-99.2%), C. gracilis (0.0-99.7%), C. simplex (0.0-95.9%), Phaeodactylum tricornutum (0.0-99.6%), Tetraselmis tetrathele (0.0-99.7%) and Dunaliella tertiolecta (0.0-99.6%), respectively. Therefore, it is assumed that food microalgae showing the high digestion such as I. galbana should be supplied to the early umbo stage larvae, and then after the umbo larval stage, the mixed microalgae with diatoms and light green algae should be supplied to the full grown stage larvae to increase the digestion of their larvae.

Resource competition between sympatric sibling rotifer species

Mechanisms underlying competitive interactions are important in understanding the structure of planktonic communities, particularly the coexistence of similar species. Here we present experimental results of exploitative competition among three sympatric sibling species of the Brachionus plicatilis complex for two differently‐sized species of food microalgae. These three rotifer species are to be found in seasonal succession in brackish ponds on the Spanish Mediterranean coast; they can, however, co‐occur for long periods. The functional and numerical responses of the three Brachionus species to both food microalgae, although similar, differed. Neither rotifer population growth nor grazing rates showed a clear positive correlation between rotifer and alga sizes. Tilman's models were applied to these results in order to predict the outcome of competition in two rotifer, two resources systems. For testing predictions and addressing the possibility of rotifer coexistence, we performed pairwise competition experiments in semicontinuous cultures, which introduces periodic disturbance as an additional factor. Results confirmed the pattern expected from Tilman's models regarding the competitive superiority of each rotifer species, when food composition was biased toward one of the two resources. This shows the relevance of the food threshold concept to predict the superior competitor. However, coexistence of rotifers was found in conditions in which Tilman's models had predicted an unstable equilibrium, with the winning species depending on the initial conditions. We hypothesize that variance in food availability mediated coexistence. Our results suggest that both food partitioning and disturbance are important in explaining the coexistence of these sibling species in nature.

1. Methods for Cryopreservation of Some Species of the Food Microalgae (NRIA Culture Collection)

1. Methods for Cryopreservation of Some Species of the Food Microalgae (NRIA Culture Collection)

Economics of microalgae ( Chaetoceros calcitrans) production using the multi-step method in the Philippines

The use of live microalgae for food during the early stages of the life cycle of shrimp larvae is considered essential. The microalga Chaetoceros calcitrans was mass produced at the Aquaculture Department of the Southeast Asian Fisheries Development Center (SEAFDEC/AQD) using the multistep method. The alga was grown in batches using successively larger containers. A cell density of 2.65 × 10 6 cells/ml was obtained from the final 4-day culture of C. calcitrans. Production cost using this method was P715.50/ton (US$ 1.00=25 Philippine pesos). The minimal costs involved in this method make it an affordable technique for the mass culture of microalgae.

Performances Et Contraintes Des Élevages Intensifs Du Cladocère Daphnia Magna Straus, Utilisations Des Biomasses Produites

[Daphnia magna is easy to bread and allows important productions. Experiments in the Museum d'Histoire naturelle (Paris), in 2 m3 tanks, showed productions between 200 and 400 g m3 week-1 in summer conditions (temperatures: 18-25°C). Daphnia received as food microalgae cultivated on pig manure. In winter, Daphnia productions remained poor (<30 g m3 week-1) in spite of microalgae provided in large quantities. Because of its important capacity of filtration, Daphnia magna has a purifying effect on its environment which causes an increase of water transparency, very favourable to macrophytic algae. These algae can develop in mass, making collecting of Daphnia difficult. The algae can be eliminated by an application of simazine (2 g m3). Daphnia magna is very sensitive to inorganic pollutants but supports easily organic substances. This organism can absorb dissolved organic substances, bacteria, and chiefly very important quantities of microalgae proliferating on domestic or urban wastes and intensive breeding manures. Daphnia is very rich in proteins (to 60% of dry weight) and its amino acid composition is favourable to nutritional requirements of young fish. They can be used living (for example as food for young pike) but it is also possible to use different ways of conservation: desiccation, freezing, silage, with preservatives. So, many utilizations are possible: feeding aquarium fish, distribution to young fish eating no living food (Cyprinids). They can also to be added to artificial food for aquatic and terrestrial animals. Lastly, extraction of chitin of the carapace can be envisaged for many industrial purposes., Daphnia magna is easy to bread and allows important productions. Experiments in the Museum d'Histoire naturelle (Paris), in 2 m3 tanks, showed productions between 200 and 400 g m3 week-1 in summer conditions (temperatures: 18-25°C). Daphnia received as food microalgae cultivated on pig manure. In winter, Daphnia productions remained poor (<30 g m3 week-1) in spite of microalgae provided in large quantities. Because of its important capacity of filtration, Daphnia magna has a purifying effect on its environment which causes an increase of water transparency, very favourable to macrophytic algae. These algae can develop in mass, making collecting of Daphnia difficult. The algae can be eliminated by an application of simazine (2 g m3). Daphnia magna is very sensitive to inorganic pollutants but supports easily organic substances. This organism can absorb dissolved organic substances, bacteria, and chiefly very important quantities of microalgae proliferating on domestic or urban wastes and intensive breeding manures. Daphnia is very rich in proteins (to 60% of dry weight) and its amino acid composition is favourable to nutritional requirements of young fish. They can be used living (for example as food for young pike) but it is also possible to use different ways of conservation: desiccation, freezing, silage, with preservatives. So, many utilizations are possible: feeding aquarium fish, distribution to young fish eating no living food (Cyprinids). They can also to be added to artificial food for aquatic and terrestrial animals. Lastly, extraction of chitin of the carapace can be envisaged for many industrial purposes.]

Availability of Deep Seawater and Effects of Bacteria Isolated from Deep Seawater on the Mass Culture of Food Microalga Chaetoceros ceratosporum.

The possible availability of deep seawater (DSW; seawater under the euphotic layer) and bacteria isolated from DSW (BDS) for the mass culture of food microalga Chaetoceros ceratosporum was investigated. Seawater samples pumped up from a depth of 320m at the kochi Deep Seawater Laboratory in Muroto, Kochi Prefecture, were collected and used for cultivation of C. ceratosporum. Growth rate (ƒE: reciprocal of the dubling time) and maximum cell yields (MCY) of the alga in untreated DSW were 1.25-2.22 (average 1.72).day-1 and 2-11 (average 6) x 105 cells/ml, respectively. When compared with those obtained by ASP6 medium, the average ,ƒEin DSW was about 90% and the values of MCY were 5-20% of those in ASP6. The values of MCY, however, showed a relatively large variance according to the sampling season of DSW. When some BDS were added to DSW, the growth of C. ceratosporum was often stimulated significantly; the ƒE values were 1.82-2.86 (average 2.27). day-1 and MCYs were 4-12 (average 8) x 105 cells/ml. Moreover, the variance of ƒE and MCY according to the sampling season tended to decrease when BDS were added. These results suggest that DSW has a high potential for cultivating food microalgae, and it can be made more stable and effective by adding BDS.

Massive cultivation of microalgae: Results and prospects

An account is given of the development of the utilization of microalgae for food and feed with special emphasis on the advantages of algal technologies for tropical and subtropical countries. The present status of microalgae mass production is characterized with respect to technology, product properties, yields, nutrition, toxicology and economics. As a multipurpose operation, the treatment of liquid wastes with algae-bacteria systems is the most promising microalgal technology. It yields proteinaceous microbial biomass as a comparatively inexpensive by-product of the operation of high-rate algal ponds, either at the simplified rural level or at the technically more elaborate industrial level. The aspect of hard-currency saving by employing algae-bacteria systems in sewage treatment for animal feed production is stressed.