Enriching table eggs with n-3 polyunsaturated fatty acids through dietary supplementation with the phototrophically grown green algae Nannochloropsis limnetica: effects of microalgae on nutrient retention, performance, egg characteristics and health parameters

The fatty acid content of microalgae, especially the high content of omega-3 fatty acids such as eicosapentaenoic acid (EPA, C20:5) and docosahexaenoic acid (DHA, C22:6), could enrich eggs when fed to laying hens. Moreover, the properties and bioactive components of omega-3 fatty acids could positively influence the health and production performance of laying hens. In this study, the effects of dried Nannochloropsis limnetica inclusions in diets on yolk omega-3 fatty acid content, laying hen performance, nutrient retention, intestinal morphometry and systemic inflammatory markers were measured. A total of 240 twenty-five-wk-old laying hens were randomly assigned to 5 treatments distributed among 30 pens. Treatment A received the reference diet, while diets in treatments B, C, and D contained the control diet with 1, 2, and 3% microalgae added, respectively. In treatment E, a portion of ingredients of the control diet was replaced with rapeseed meal to induce a mild nutritional challenge, along with an inclusion of 3% microalgae. Compared to the control group the rate of lay increased by approximately 5% (P = 0.039) when birds were fed 2 or 3% microalgae. Furthermore, inclusion of 2 and 3% microalgae resulted in higher feed intake compared to the control group (126, 125, and 119 g/hen/d respectively; P = 0.001). Other performance parameters such as nutrient retention and egg characteristics were not affected by the dietary treatments. The EPA and DHA content of the yolk increased with increasing microalgae inclusion level (P < 0.001). A 2% algal inclusion resulted in 58.3 (EPA) and 603 (DHA) mg per 100 g dry yolk, respectively. Plasma haptoglobin levels of laying hens in both treatments receiving 3% microalgae were almost 3 times lower compared to the control group (1.25 and 1.62 vs. 5.60; P < 0.001), regardless of the inclusion of rapeseed in the diet. Based on these results, it can be concluded that the inclusion of N. limnetica enriches the egg yolk without negatively affecting the performance of laying hens and egg characteristics. Due to the positive effect on feed intake, microalgae in the diet provide nutritional benefits for laying hens. However, the positive effects of microalgae, especially on the health of laying hens, warrants further research.

Effect of growth conditions on the efficiency of cell disruption of Neochloris oleoabundans

The impact of four different growth conditions on the cell disruption efficiency of Neochloris oleoabundans was investigated. A mechanical and biological cell disruption methods were evaluated separately and combined. It has been established that microalgae grown in marine water under nitrogen deprivation were the most resistant against cell disruption methods and released the lowest amount of proteins. The release of lipids, however, followed the "hindered molecule diffusion phenomenon" because it did not follow the same release pattern as proteins. The enzymatic treatment was efficient enough to release the majority of the proteins without combining it with high-pressure homogenization. Regarding energy input, Neochloris oleoabundans grown in marine water under nitrogen deprivation required the highest energy input to release proteins (E_p = 13.76 kWh.kg^-1) and to break the cells by high-pressure homogenization (E_{x - HPH} = 1.14 kWh.kg^-1) or by the combination of enzymes and High-pressure homogenization (E_{x - ENZ} = 2.79 kWh.kg^-1).

Selective and energy efficient extraction of functional proteins from microalgae for food applications

The use of a single controlled bead milling step of the microalga Tetraselmis suecica resulted in a soluble fraction, rich in functional proteins. This was achieved by fine-tuning the processing time, thereby exploiting the difference in rates of protein and carbohydrate release during milling. Soluble proteins were extracted under mild conditions -room temperature, no addition of chemicals, pH 6.5-, with a yield of 22.5% and a specific energy consumption of 0.6 kWh kg_DW^-1, which is within the recommended minimum energy for an extraction step in a biorefinery process. The resulting protein extract contained 50.4% (DW) of proteins and 26.4% carbohydrates, showed light green color and displayed superior surface activity and gelation behavior compared to whey protein isolate. The proposed process is simple (only one bead milling step), scalable, and allows the mild extraction of functional proteins, making it interesting for industrial applications in the food industry.

Techno-Functional Properties of Crude Extracts from the Green Microalga Tetraselmis suecica

A mild fractionation process to extract functional biomolecules from green microalgae was implemented. The process includes bead milling, centrifugation, and filtration with several membrane cut-offs. For each fraction, the corresponding composition was measured, and the surface activity and gelation behavior were determined. A maximum protein yield of 12% was obtained in the supernatant after bead milling and between 3.2 and 11.7% after filtration. Compared to whey protein isolate, most of the algae fractions exhibited comparable or enhanced functionality. Surface activity for air-water and oil-water interfaces and gelation activities were notably superior for the retentate fractions compared to the permeates. It is proposed that such functionality in the retentates is due to the presence of hydrophobic compounds and molecular complexes exhibiting a similar behavior as Pickering particles. We demonstrated that excellent functionality can be obtained with crude fractions, requiring minimum processing and, thus, constituting an interesting option for commercial applications.

Energy consumption and water-soluble protein release by cell wall disruption of Nannochloropsis gaditana

Several cell disruption methods were tested on Nannochloropsis gaditana, to evaluate their efficiency in terms of cell disintegration, energy input and release of soluble proteins. High-pressure homogenization (HPH) and bead milling were the most efficient with >95% cell disintegration, ±50% (w/w) release of total proteins and low energy input (<0.5kWh.kg^-1_biomass). Enzymatic treatment required low energy input (<0.34kWh.kg^-1_biomass), but it only released ±35% protein (w/w). Pulsed Electric Field (PEF) was neither energy-efficient (10.44kWh.kg^-1_biomass) nor successful for protein release (only 10% proteins w/w) and cell disintegration. The release of proteins after applying HPH and bead milling always required less intensive operating conditions for cell disruption. The energy cost per unit of released protein ranged from 0.15-0.25 €.kg_Protein^-1 in case of HPH, and up to 2-20 €.kg_Protein^-1 in case of PEF.

Biorefinery of microalgal soluble proteins by sequential processing and membrane filtration

A mild biorefinery process was investigated on the microalga Nannochloropsis gaditana, to obtain an enriched fraction of water soluble proteins free from chlorophyll. After harvesting, a 100g.L^-1 solution of cells was first subjected to cell disruption by either high-pressure homogenization (HPH) or enzymatic treatment (ENZ). HPH resulted in a larger release of proteins (49%) in the aqueous phase compared to the Alcalase incubation (35%). In both cases, an ultrafiltration/diafiltration (UF/DF) was then performed on the supernatant obtained from cell disruption by testing different membrane cut-off (1000kDa, 500kDa and 300kDa). After optimising the process conditions, the combination of ENZ→UF/DF ended in a larger overall yield of water soluble proteins (24.8%) in the permeate compared to the combination of HPH→UF/DF (17.4%). A gel polarization model was implemented to assess the maximum achievable concentration factor during ultrafiltration and the mass transfer coefficient related to the theoretical permeation flux rate.

Properties of the Cell Walls of Lactococcus lactis subsp. cremoris SK110 and SK112 and Their Relation to Bacteriophage Resistance

Resistance of Lactococcus lactis subsp. cremoris SK110 to bacteriophage sk11G, encoded on the plasmid pSK112, is due to poor phage adsorption. Its phage-sensitive variant SK112, cured of pSK112, adsorbs phages effectively. Incubation of SK112 with concanavalin A remarkably reduced phage adsorption to this strain. This treatment also caused agglutination of SK112 that was not found with SK110, indicating different concanavalin A adsorption characteristics of cell walls of both strains. The differences between the two strains were reduced by a mild alkali treatment of cells. This resulted in a positive agglutination with concanavalin A for both strains and in parallel adsorption of phage sk11G to both. Moreover, isolated cell walls of the two strains were investigated, and both bound phage sk11G. These observations suggest the presence of phage receptor material in SK112 as well as in SK110. SK110 contained a relatively high level of bound galactose when compared with the phage-sensitive SK112. After the mild alkali treatment, however, the galactose content of SK110 was diminished such that it became comparable with that of SK112. It is hypothesized that the alkali treatment liberates a galactose-containing component from the cell wall and causes phage sensitivity in L. lactis subsp. cremoris SK110.

Degradation of Perennial Ryegrass Leaf and Stem Cell Walls by the Anaerobic Fungus Neocallimastix sp. Strain CS3b

The degradation of cell walls isolated from stems and leaves of perennial ryegrass by the anaerobic fungus Neocallimastix sp. strain CS3b was studied in a defined medium. The combined cellulose and hemicellulose fraction represented 53.1 (wt/wt) and 63.3% (wt/wt) of the dry weight of control grass leaf and stem cell walls, respectively. In both leaf and stem cell walls, glucose was the major neutral monosaccharide, followed by xylose, arabinose, and galactose. After 2 days of fermentation with Neocallimastix sp. strain CS3b, treated cell walls contained smaller amounts of neutral sugars compared with those of undigested cell walls. These results were more evident for glucose, xylose, and arabinose than for galactose. Furthermore, the sugar content of leaf cell walls decreased before a decline in the sugar content of stem cell walls was observed. Data from formate and hydrogen production indicated that the growth of Neocallimastix sp. strain CS3b was completed in 4 days in the culture system used. During this period, the fungus liberated about 95% of the fermentable sugars in untreated material. On a percentage basis, no significant differences were found in final extent of degradation of glucose, xylose, and arabinose. Galactose, however, was degraded to a lesser extent.

Competition for sulfate and ethanol among desulfobacter, desulfobulbus, and desulfovibrio species isolated from intertidal sediments

Competition for sulfate and ethanol among Desulfobacter, Desulfobulbus, and Desulfovibrio species isolated from estuarine sediments was studied in energy-limited chemostats. Desulfovibrio baculatus was the most successful competitor for limiting amounts of sulfate and ethanol, followed by Desulfobulbus propionicus. The success of Desulfovibrio baculatus was dependent on the availability of sufficient iron. Of the three species studied, Desulfobacter postgatei was the least successful competitor for limiting amounts of sulfate. Although stimulating the growth of Desulfobacter postgatei, addition of Ca-saturated illite particles to culture media did not affect the outcome of competition for sulfate. Thus, under sulfate limitation acetate accumulated. This phenomenon was briefly discussed in relation to the flow of electrons during anaerobic mineralization in marine and estuarine sulfate-limited sediments.

Biotechnological production and applications of the omega-3 polyunsaturated fatty acid docosahexaenoic acid

Docosahexaenoic acid (DHA) is a polyunsaturated fatty acid composed of 22 carbon atoms and six double bonds. Because the first double bond, as counted from the methyl terminus, is at position three, DHA belongs to the so-called omega-3 group. In recent years, DHA has attracted much attention because of its beneficial effect on human health. At present, fish oil is the major source of DHA, but alternatively it may be produced by use of microorganisms. Marine microorganisms may contain large quantities of DHA and are considered a potential source of this important fatty acid. Some of these organisms can be grown heterotrophically on organic substrates without light. These processes can be well controlled and DHA with constant quality can be produced all year round. This paper reviews recent advances in the biotechnological production of DHA by marine microorganisms.

Fed-batch cultivation of the docosahexaenoic-acid-producing marine alga Crypthecodinium cohnii on ethanol

The heterotrophic marine microalga Crypthecodinium cohnii produces docosahexaenoic acid (DHA), a polyunsaturated fatty acid with food and pharmaceutical applications. So far, DHA production has been studied with glucose and acetic acid as carbon sources. This study investigates the potential of ethanol as an alternative carbon source for DHA production by C. cohnii. In shake-flask cultures, the alga was able to grow on ethanol. The specific growth rate was optimal with 5 g l(-1) ethanol and growth did not occur at 0 g l(-1) and above 15 g l(-1). By contrast, in fed-batch cultivations with a controlled feed of pure ethanol, cumulative ethanol addition could be much higher than 15 g l(-1), thus enabling a high final cell density and DHA production. In a representative fed-batch cultivation of C. cohnii with pure ethanol as feed, 83 g dry biomass l(-1), 35 g total lipid l(-1) and 11.7 g DHA l(-1) were produced in 220 h. The overall volumetric productivity of DHA was 53 mg l(-1 )h(-1), which is the highest value reported so far for this alga.

Synthetic peptides derived from the β2−β3 loop ofRaphanus sativusantifungal protein 2 that mimic the active site

Rs-AFPs are antifungal proteins, isolated from radish (Raphanus sativus) seed or leaves, which consist of 50 or 51 amino acids and belong to the plant defensin family of proteins. Four highly homologous Rs-AFPs have been isolated (Rs-AFP1-4). The structure of Rs-AFP1 consists of three beta-strands and an alpha-helix, and is stabilized by four cystine bridges. Small peptides deduced from the native sequence, still having biological activity, are not only important tools to study structure-function relationships, but may also constitute a commercially interesting target. In an earlier study, we showed that the antifungal activity of Rs-AFP2 is concentrated mainly in the beta2-beta3 loop. In this study, we synthesized linear 19-mer peptides, spanning the entire beta2-beta3 loop, that were found to be almost as potent as Rs-AFP2. Cysteines, highly conserved in the native protein, are essential for maintaining the secondary structure of the protein. Surprisingly, in the 19-mer loop peptides, cysteines can be replaced by alpha-aminobutyric acid, which even improves the antifungal potency of the peptides. Analogous cyclic 19-mer peptides, forced to adopt a hairpin structure by the introduction of one or two non-native disulfide bridges, were also found to possess high antifungal activity. The synthetic 19-mer peptides, like Rs-AFP2 itself, cause increased Ca2+ influx in pregerminated fungal hyphae.

Characterisation of extracellular polysaccharides produced by Crypthecodinium cohnii

The valuable polyunsaturated fatty acid, docosahexaenoic acid, can be produced by cultivation of the heterotrophic microalga, Crypthecodinium cohnii. During batch growth of C. cohnii on glucose, sea salt and yeast extract for 5 days, so far unreported extracellular polysaccharides were produced. These caused an increased viscosity and a strong drop in the maximum oxygen transfer. The viscosity increased most markedly as cells entered the stationary phase. The polysaccharides varied in size (from 6 kDa to >1,660 kDa) and monomer distribution. A high molecular mass fraction (from 100 kDa to >1,660 kDa) and a medium molecular mass fraction (6-48 kDa) were prepared. The high molecular mass fraction contained (on a molar basis) 71.7% glucose, 13.1% galactose and 3.8% mannose, whereas the medium molecular mass fraction contained 37.7% glucose, 19.8% galactose and 28.1% mannose. Other monomers present in both fractions were fucose, uronic acid and xylose. Monomers were coupled mainly via alpha-(1-3) links. Increased viscosity due to polysaccharide production complicates the development of commercial, high cell-density processes for the production of docosahexaenoic acid.

Comparison of solubility of pea protein hydrolysate by three analytical methods

Pea protein hydrolysate was obtained by enzymatic hydrolysis with trypsin. The degree of hydrolysis (DH) was controlled by using the pH-stat method. Solubility of the trypsin-treated hydrolysate was tested at nine different pH values starting from 2 up to 10. Protein determinations were carried out using Kjeldahl, Lowry and modified Lowry methods. The results revealed that samples analysed with either the Kjeldahl or Lowry method gave similar values. However, systematic consistent differences existed for those results obtained by the Kjeldahl and the modified Lowry as well as between those results obtained by the Lowry and the modified Lowry.

Antifungal activity of synthetic 15-mer peptides based on the Rs-AFP2 (Raphanus sativus antifungal protein 2) sequence

Plant defensins are a class of cysteine-rich peptides of which several members have been shown to be potent inhibitors of fungal growth. A series of overlapping 15-mer peptides based on the amino acid sequence of the radish antifungal protein Rs-AFP2 have been synthesized. Peptides 6, 7, 8 and 9, comprising the region from cysteine 27 to cysteine 47 of Rs-AFP2 showed substantial antifungal activity against several fungal species (minimal inhibitory concentrations of 30-60 micrograms/mL), but no activity towards bacteria (except peptide 6 at 100 micrograms/mL). The active peptides were shown to be sensitive to the presence of cations in the medium and to the composition and pH of the medium. When present at a subinhibitory concentration (20 micrograms/mL), peptides 1, 7, 8 and 10 potentiated the activity of Rs-AFP2 from 2.3-fold to 2.8-fold. By mapping the characteristics of the active peptide on the structure of Rs-AFP2 as determined by nuclear magnetic resonance, the active region of the antifungal protein appears to involve beta-strands 2 and 3 in combination with the loop connecting those strands. A cyclized synthetic mimic of the loop, cysteine 36 to cysteine 45, was shown to have antifungal activity. Substitution of tyrosine 38 by alanine in the cyclic peptide substantially reduced the antifungal activity, indicating the importance of this residue for the activity of Rs-AFP2 as demonstrated carrier by mutational analysis.

In Lactococcus lactis subsp. cremoris SK110 protein, instead of lipoteichoic acid, reacts with the group-N-specific antiserum

The reaction between cell-surface components, isolated from two Lactococcus lactis subsp. cremoris strains, with their Group-specific antiserum were studied. No reaction between purified lipoteichoic acid and the antiserum was observed. Both strains, however, did belong to the lactococci (Group-N streptococci), as was demonstrated by the positive reaction between the antiserum and an acid- (Lancefield) or alkaline-extract. Experiments with proteolytic enzymes demonstrated the involvement of protein in the antigenic material in the latter reaction.

Isolation and characterization of lipoteichoic acid, a cell envelope component involved in preventing phage adsorption, from Lactococcus lactis subsp. cremoris SK110

The cell envelope of the phage-resistant Lactococcus lactis subsp. cremoris SK110 differed from its phage-sensitive variant by the presence of a galactosyl-containing component. This component was present in material obtained from SK110 by a mild alkali treatment. In a similar fraction extracted from SK112, no galactosyl-containing components were detected. With respect to gel permeation chromatography and electrophoretic mobility, identical characteristics of the alkali-extracted material and purified lipoteichoic acid (LTA) were measured. Chemical analysis of the latter component showed the absence of galactose in LTA isolated from SK112, whereas it was present in LTA obtained from SK110. In this paper, we propose that galactosyl-containing LTA is involved in preventing phage adsorption to L. lactis subsp. cremoris SK110.

Cell Surface Characteristics of Bacteriophage-Resistant Lactococcus lactis subsp. cremoris SK110 and Its Bacteriophage-Sensitive Variant SK112

Several cell surface characteristics of bacteriophage-resistant Lactococcus lactis subsp. cremoris SK110 were compared with those of its phage-sensitive derivative SK112. After centrifugation, SK110 cells resisted suspension more strongly than SK112 cells. SK112 was more negatively charged and had a more hydrophobic cell surface than SK110. Furthermore, SK112 was agglutinated in the presence of concanavalin A, whereas SK110 was not. The opposite was observed upon incubation of cells of either strain with a lectin from Ricinus communis. A mild alkali treatment decreased the differences in the cell surface characteristics of the two strains remarkably.