Marine microalgae as a potential source of minerals in fish diets

The incorporation of powdered marine microalgae in fish diets can substitute, at least in part, for the addition of minerals to the diet. In diets for freshwater fishes, the incorporation of 33% of powdered marine microalgae can supply some of the mineral element requirements. The incorporation of microalgal powder in diets for marine fishes appears more effective, since lower percentages are needed to cover the mineral requirements. Most mineral needs of turbot can be covered with low percentages of marine microalgal powder in the diet: 3.8% of Tetraselmis suecica, 5.7% of Isochrysis galbana, 3.57% of Dunaliella tertiolecta and 3.9% of Chlorella stigmatophora. Mn and Co must, however, be added. Thus, incorporation of small amounts of marine microalgae in diets can replace a mineral mixture

Vitamin content of four marine microalgae. Potential use as source of vitamins in nutrition

Certain marine microalgae contain water-and lipid-soluble vitamins and can be used as food supplements or food ingredients. A number of vitamins are present in higher concentrations in the microalgae than in conventional foods traditionally considered rich in them. Ingestion of relatively small quantities of microalgae can cover the requirements for some vitamins in animal nutrition, including human nutrition, while supplementing others. Marine microalgae can thus be considered to represent a non-conventional source of vitamins or a vitamin supplement for animal or human nutrition.Comision Asesora de Investigacion Cientifica y Tecnica; AC86-000

β-carotene, vitamin C and vitamin E content of the marine microalga Dunaliella tertiolecta cultured with different nitrogen sources

Variations in the β-carotene, vitamin C and vitamin E content of D. tertiolecta have been shown to result from the nitrogen source used in the culture medium. Differences of 101%, 38% and 69% have been found in β-carotene, ascorbic acid and tocopherol content in mg/g of dry matter, respectively, and differences of 147%, 63% and 37% occurred in β-carotene, vitamin C and E concentrations in mg/litre of culture, respectively. Considering the β-carotene, vitamin C and vitamin E content in mg/g of chlorophyll a, maximum variations occurred in β-carotene content, with differences of 145% among the different nitrogen sources. Maximum β-carotene and vitamin C values were found in urea cultures, whereas urea cultures showed the minimum values for vitamin E. Variations in the β-carotene, vitamin C and vitamin E content of D. tertiolecta have been shown to result from the nitrogen source used in the culture medium. Differences of 101%, 38% and 69% have been found in β-carotene, ascorbic acid and tocopherol content in mg/g of dry matter, respectively, and differences of 147%, 63% and 37% occurred in β-carotene, vitamin C and E concentrations in mg/litre of culture, respectively. Considering the β-carotene, vitamin C and vitamin E content in mg/g of chlorophyll a, maximum variations occurred in β-carotene content, with differences of 145% among the different nitrogen sources. Maximum β-carotene and vitamin C values were found in urea cultures, whereas urea cultures showed the minimum values for vitamin E

Biochemical composition and growth of the marine microalga Dunaliella tertiolecta (Butcher) with different ammonium nitrogen concentrations as chloride, sulphate, nitrate and carbonate.

Cultures of the marine microalga Dunaliella tertiolecta were grown in ammonium chloride, sulphate, nitrate and carbonate at concentrations ranging from 0.25 to 16 mg.atom N/l. Cells were harvested in the stationary phase and cell density and biochemical composition determined. Biomass production at the end of the stationary phase, expressed as cell density, was affected by the concentration of ammonium-N in the medium but not by the ammonium compound used. Optimal growth conditions for obtaining maximum cell density, between 1.86×106 and 2.81×106 cells/ml, were 2, 4 and 8 mg.atom N/l. The compound and concentration of ammonium-N had little effect on the growth velocity of D. tertiolecta cultures in the logarithmic phase, with values of 0.35±0.06 doublings/day under all the conditions assayed. The ammonium compound and the concentration of nitrogen affected the concentration of different cellular constituents such as protein, carbohydrate, lipid and chlorophyll a, although these changes were not necessarily related to cell density in the culture. Protein, the most affected fraction, tended to increase with an increase in the nitrogen concentration for all the ammonium compounds used. Maximum protein/ml was obtained with ammonium carbonate at all the nitrogen concentrations used. Maximum protein/cell occurred at the higher nitrogen concentrations (16 and 32 mg/atom N/l) for all the ammonium compounds. Considering the optimum growth interval (2-8 mg.atom N/l), maximum protein/cell concentrations were also obtained in the cultures with ammonium carbonate. Carbohydrate and lipid concentrations varied less than protein concentration. Maximum values of carbohydrate/ml were also found in the ammonium carbonate cultures. Maximum lipid/cell concentrations occurred at the lowest nitrogen concentrations, in contrast to protein values. As a percentage of the total organic matter, protein increased and lipid decreased with the nitrogen concentration, whereas carbohydrate remained constant. Consequently, lipid seemed to be the storage product in this marine microalga. Gross energy values in the different cultures were a function of nitrogen concentration, maximum differences occurring in the ammonium carbonate cultures. The biochemicalvariability of this microalga must have a marked effect on its value as a source of single-cell protein, as chemicals or as feed in mariculture

Nutritional properties of four marine microalgae for albino rats

The nutritive value of the marine microalgaeTetraselmis suecica, Isochrysis galbana, Dunaliella tertiolecta and Chlorella stigmatophora was studied in diets given to rats. Biological assays were carried out in order to determine the Protein Efficiency Ratio (PER) and the Food Conversion Efficiency (FCE). Each dried microalga was fed to weaning Wistar albino rats as the sole protein source at a protein level of 12%. Control rats were given diets containing 12 % casein. Food consumption was similar in all groups. PER values obtained were 1.14 with T. suecica diet, 1.13 with I. galbana diet, 2.07 with D. tertiolecta diet and 1.13 with C. stigmatophora diet (casein, 2.50). FCE values followed a similar pattern. The data showed that the marine microalga D. tertiolecta is a source of protein of good quality. Its PER is quite high, compared to vegetable and cereal proteins, and compares favourably with other microbial protein sources, such as yeasts or different freshwater microalgae. Haematological tests showed no significant differences among the groups in haemoglobin levels, red and white blood cell counts, differential count and mean corpuscular volume. Different blood parameters were also determined and a significant decrease in triglycerides levels appeared with all the microalgal diets, whereas a significant decrease in cholesterol appeared in D. tertiolecta and C. stigmatophora diets

Growth, chlorophyll α and protein of the marine microalga Isochrysis galbana in batch cultures with different salinities and high nutrient concentrations

Cultures of the marine microalga Isochrysis galbana were grown under 56 different nutrient concentration-salinity conditions, ranging from 1 to 64 mM NaNO3 and from 0 to 35‰ salinity. Salinity and nutrient concentration were found to be closely related to I. galbana growth and to the biochemical composition. Optimal growth conditions were between 15 and 35‰ salinity and nutrient concentrations of 2, 4 and 8 mM NaNO3, resulting in one doubling/day and a maximum cellular density of 20 × 106cells/ml. Variations in salinity and in nutrient concentration had a greater effect on the final biomass than on the growth velocity. Maximum values of chlorophyll α ml were found with 2, 4 and 8 mM NaNO3 and between 15 and 35‰ salinity. Chlorophyll α cell values were more homogeneously distributed between 15 and 35‰ salinity and 1 to 8 mM NaNO3, although maximum concentrations (37 pg chlorophyll α cell) were reached at 10-15‰ with all the nutrient concentrations. Protein per ml of culture and protein per cell were closely related to salinity and nutrient concentration. Maximum values of 387 μg/ml and 18.6 pg/cell were obtained at 15-35‰ salinity and 4-8 mM NaNO3. The nitrate-protein transformation rate was related to nutrient concentration. Maximum rate was 84% at 15‰ salinity and 1 mM NaNO3. Nutrient concentrations higher than 16 mM NaNO3 produced a strong decrease in the efficiency at all salinities

Biomass production and biochemical composition in mass cultures of the marine microalga Isochrysis galbana Parke at varying nutrient concentrations

Mass cultures of Isochrysis galbana were carried out with four nutrient concentrations ranging from 2 to 16 mM of NaNO3 and salinity 35‰. An air flow of 15 l/min maintained a CO2 transference rate sufficient to keep the pH below 8.4. Using these conditions, equations were calculated by a multiple non-linear least squares regression of order four, enabling predictions to be made of growth kinetics and chemical composition. Maximum cellular density of 65.5 × 106 cells/ml was obtained with 4 mM NaNO3. Cellular volume was constant in the different nutrient concentrations. Protein content reached a maximum value of 374 μg/ml at 4 mM of NaNO3, and this concentration also presented the maximum efficiency of transformation from nitrate to protein, i.e. 114%. As a result, lowest costs for harvesting are obtained at a nutrient concentration of 4 mM NaNO3. Efficiencies decreased to 15% as nutrient concentration increased. Maximum values of chlorophyll a (21.9 μg/ml) and carbohydrates (213 μg/ml) were also obtained with 4 mM NaNO3. In the logarithmic phase, the contents of protein, chlorophyll a, carbohydrates, RNA and DNA per cell were constant. Chlorophyll a reached values between 0.15 and 0.33 pg/cell in the stationary phase. Carbohydrate levels reached the maximum value of 3.16 pg/cell with 4 mM NaNO3 in the stationary phase. The levels of RNA/cell and DNA/cell were constant in all the nutrient concentrations tested and in both growth phases, and ranged from 1.15 to 1.71 pg/cell for RNA and from 0.006 to 0.014 pg/cell for DNA. Growth in mass cultures is closely coupled to changes in nutrient concentrations and variations occur in protein, chlorophyll a and carbohydrate contents, showing differences of 177%, 220% and 136%, respectively, in the stationary phase. This biochemical variability, mainly in protein content, must have a marked effect on the nutritive value of this microalga as a feed in mariculture

Mass culture and biochemical variability of the marine microalga Tetraselmis suecica Kylin (Butch) with high nutrient concentrations

Mass cultures of Tetraselmis suecica were carried out with four nutrient concentrations, ranging from 2 to 16 mM of NaNO3 and salinity 35‰. An air flow of 15 l/min maintained a CO2 transference rate sufficient to keep the pH below 8.4. Using these cultural conditions equations were calculated, by a multiple non-linear least squares regression of order four, enabling predictions to be made of growth kinetics and chemical composition. Maximum cellular densities of 7.83 × 106 and 7.15 × 106 cells/ml were obtained with 8 and 16 mM of NaNO3, respectively. Growth velocity ranged between 0.53 and 0.63 doublings (dbl)/day, although 0.98 dbl/day were reached with 16 mM of NaNO3. Volume increased with nutrient concentration from 252 to 905 μm3. Protein content reached maximum values of 306 μg/ml or 59.8 pg/cell. In the logarithmic phase, protein was regulated by nutrient concentration and decreased according to this concentration. Maximum efficiency of transformation from nitrate to protein was 108%, obtained at 2 mM of NaNO3. Efficiency decreased, to 14%, when nutrient concentration increased. This fact indicates that the lowest cost of harvesting is obtained with a nutrient concentration of 2 mM NaNO3. Chlorophyll a cell reached values between 3.1 and 3.8 pg/cell in the stationary phase. There was a relationship between nutrient concentration and chlorophyll α cell in the logarithmic phase, with an increase from 2.15 pg/cell to 3.74 pg/cell. Changes in chlorophyll α level are related to nitrogen depletion. Carbohydrate/cell was constant at values of 19.84-28.68 pg/cell in the logarithmic and stationary phases and was not related to nitrogen depletion. RNA/cell ranged from 4.17 to 5.48 pg/cell, except at 2 mM of NaNO3 when it was 2.77 pg/cell, probably due to nitrogen depletion. The level of DNA/cell was constant in all the nutrient concentrations assayed and ranged from 0.1 to 1.09 pg/cell. Great variability in the chemical composition of T. suecica has been shown. Growth in mass cultures is closely coupled to changes in nutrient concentrations and variations occur in protein, chlorophyll α and RNA content, showing differences of 215%, 190% and 203%, respectively, in the stationary phase. This biochemical variability, mainly in protein content, must have a marked effect on the nutritive value of this microalga as feed in mariculture

Changes in protein, carbohydrates and gross energy in the marine microalga Dunaliella tertiolecta (Butcher) by nitrogen concentrations as nitrate, nitrite and urea

Cultures of the marine microalga Dunaliella tertiolecta were grown in nitrate, nitrite and urea at concentrations ranging from 0·25 to 16 mg atom. N/litre. Great biochemical variability has been shown in this microalga as a function of high nitrogen concentrations for all the sources used. Cellular protein and carbohydrates and gross energy per ml of culture increased proportionally to the increase in the N concentration, under conditions that maintain constant the N P ratio. Two kinds of cultures are defined: low nitrogen cultures 2 mg atom. N/litre. Variability mainly appears in the second type of cultures. Protein/cell values of up to 4·94, 5·47 and 1·41 times higher have been observed in nitrate, nitrite and urea cultures, respectively, when comparing protein/cell values obtained in high N cultures with those obtained in low N cultures. Similar variations have been observed in the carbohydrates/cell content, with values up to 3·16, 3·30 and 1·77 times higher in the high than in the low N cultures. Biochemical variability is greater in nitrate and nitrite cultures (inorganic sources of nitrogen) than in urea cultures (organic source of N). Lipid/carbohydrates ratio seems to be a convenient parameter for characterizing the physiological state of a microalgal population. This biochemical variability must have a marked effect on the value of this microalga as a source of single cell protein, chemicals or as feed in mariculture