Supercritical CO2 Extraction of High-Added Value Compounds from Chlorella vulgaris: Experimental Design,Modelling and Optimization

Microalgae are well-known for their high-added value compounds and their recovery is currently of great interest. The aim of this work is the recovery of such components from Chlorella vulgaris through supercritical fluid extraction (SFE) with CO₂. The effect of the extraction temperature (40–60 °C), pressure (110–250 bar), and solvent flow rate (20–40 g/min) was tested on yield, the extract’s antioxidant activity, and the phenolic, chlorophyll and carotenoid content. Thus, data analysis indicated that the yield was mainly affected by temperature, carotenoids by pressure, while the extract’s phenolics and antioxidant activity were affected by the synergy of temperature and pressure. Moreover, SFE’s kinetic study was performed and experimental data were correlated using Sovová’s mass transfer-based model. SFE optimization (60 °C, 250 bar, 40 g/min) led to 3.37% w/w yield, 44.35 mg_extr/mg_DPPH antioxidant activity (IC50), 18.29 mg_GA/g_extr total phenolic content, 35.55, 21.14 and 10.00 mg/g_extr total chlorophyll, carotenoid and selected carotenoid content (astaxanthin, lutein and β-carotene), respectively. A comparison of SFE with conventional aq. ethanol (90% v/v) extraction proved SFE’s superiority regarding extraction duration, carotenoids, antioxidant activity and organoleptic characteristics of color and odor despite the lower yield. Finally, cosolvent addition (ethanol 10% w/w) at optimum SFE conditions improved the extract’s antioxidant activity (19.46%) as well as yield (101.81%).     

Study of the Physicochemical and Biological Properties of the Lipid Complex of Marine Microalgae Isolated from the Coastal Areas of the Eastern Water Area of the Baltic Sea

The Baltic Sea algae species composition includes marine euryhaline, freshwater euryhaline, and true brackish water forms. This study aimed to isolate a lipid–pigment complex from microalgae of the Baltic Sea (Kaliningrad region) and investigate its antimicrobial activity against Gram-positive and Gram-negative bacteria. Microalgae were sampled using a box-shaped bottom sampler. Sequencing was used for identification. Spectroscopy and chromatography with mass spectroscopy were used to study the properties of microalgae. Antibiotic activity was determined by the disc diffusion test. Lipids were extracted using the Folch method. Analysis of the results demonstrated the presence of antimicrobial activity of the lipid–pigment complex of microalgae against E. coli (the zone diameter was 17.0 ± 0.47 mm and 17.0 ± 0.21 mm in Chlorella vulgaris and Arthrospira platensis, respectively) and Bacillus pumilus (maximum inhibition diameter 16.0 ± 0.27 mm in C. vulgaris and 16.0 ± 0.22 mm in A. platensis). The cytotoxic and antioxidant activities of the lipid complexes of microalgae C. vulgaris and A. platensis were established and their physicochemical properties and fatty acid composition were studied. The results demonstrated that the lipid–pigment complex under experimental conditions was the most effective against P. pentosaceus among Gram-positive bacteria. Antimicrobial activity is directly related to the concentration of the lipid–pigment complex. The presence of antibacterial activity in microalgae lipid–pigment complexes opens the door to the development of alternative natural preparations for the prevention of microbial contamination of feed. Because of their biological activity, Baltic Sea microalgae can be used as an alternative to banned antibiotics in a variety of fields, including agriculture, medicine, cosmetology, and food preservation.     

光谱对小球藻和等鞭金藻生长的影响

采用单色LED光源和荧光灯从效率和速率两个角度研究了光源光谱对海生小球藻和等鞭金藻8701生长的影响,结果表明,连续光谱能够促进较高的最大生长率,蓝光促进生长的效率较高,两者组合能够较好地兼顾效率和速率。为了定量描述光照中的光谱参量,引入光谱吸收系数,根据光源发射光谱和藻体吸收谱计算海藻对光源光谱的量子吸收效率,该系数与实验结果中相应的生长效率成正相关,能够初步以量化形式反映光谱与其生长效率的关系。     

Metabolic and Proteomic Analysis of Chlorella sorokiniana,Chloroidium saccharofilum,and Chlorella vulgaris Cells Cultured in Autotrophic,Photoheterotrophic, and Mixotrophic Cultivation Modes

Chlorella is one of the most well-known microalgal genera, currently comprising approximately a hundred species of single-celled green algae according to the AlgaeBase. Strains of the genus Chlorella have the ability to metabolize both inorganic and organic carbon sources in various trophic modes and synthesize valuable metabolites that are widely used in many industries. The aim of this work was to investigate the impact of three trophic modes on the growth parameters, productivities of individual cell components, and biochemical composition of Chlorella sorokiniana, Chloroidium saccharofilum, and Chlorella vulgaris cells with special consideration of protein profiles detected by SDS-PAGE gel electrophoresis and two-dimensional gel electrophoresis with MALDI-TOF/TOF MS. Mixotrophic conditions with the use of an agro-industrial by-product stimulated the growth of all Chlorella species, which was confirmed by the highest specific growth rates and the shortest biomass doubling times. The mixotrophic cultivation of all Chlorella species yielded a high amount of protein-rich biomass with reduced contents of chlorophyll a, chlorophyll b, carotenoids, and carbohydrates. Additionally, this work provides the first information about the proteome of Chloroidium saccharofilum, Chlorella sorokiniana, and Chlorella vulgaris cells cultured in molasses supplementation conditions. The proteomic analysis of the three Chlorella species growing photoheterotrophically and mixotrophically showed increased accumulation of proteins involved in the cell energy metabolism and carbon uptake, photosynthesis process, and protein synthesis, as well as proteins involved in intracellular movements and chaperone proteins.     

Stabilization of Natural Pigments in Ethanolic Solutions for Food Applications: The Case Study of Chlorella vulgaris

Chlorella vulgaris is a green microalga with a high chlorophyll content, representing a valuable source of green pigments for food applications. As the application of whole biomass can promote an unpleasant fish-like flavor, the use of chlorophyll extract can overcome this drawback. However, chlorophylls tend to easily degrade when out of the chloroplasts, decreasing their potential as a food ingredient. Thus, to study the suitable conditions for isolated chlorophylls preservation, in this work, the influence of temperature (4 to 60 °C), light (dark or 24 h photoperiod), alkaline conditions (with or without aqueous NaOH addition), and modified atmosphere (air or argon atmosphere) on the stability of the color in ethanolic solutions obtained from C. vulgaris were studied. The loss of green color with temperature followed the first-order kinetics, with an activation energy of 74 kJ/mol. Below 28 °C and dark conditions were suitable to preserve isolated chlorophylls. The addition of NaOH and an inert argon-rich atmosphere did not exhibit a statistically positive effect on color preservation. In the case study, cooked cold rice was colored to be used in sushi. The color remained stable for up to 3 days at 4 °C. Therefore, this work showed that C. vulgaris chlorophylls could be preserved in ethanolic solutions at room or lower temperatures when protected from light, allowing them to obtain a suitable natural food ingredient to color foodstuffs.     

自养、异养和混养下小球藻的生长及生化成分

对小球藻在自养、异养和混养条件下的生长状况及细胞的生化成分(如可溶性蛋白、可溶性糖、叶绿素及脂肪酸组成)进行了研究．结果表明：异养和混养培养的小球藻的生物量远大于自养时的生物量;异养和混养培养的小球藻的比生长速率分别是自养时的2．13倍和3倍;光照对混养条件下的细胞生长有影响,但光照强度为2．5klx和4．0klx时细胞生长的差别并不明显．尤其在稳定生长期;与自养生长相比,异养过程中小球藻的脂肪含量明显增加,可溶性蛋白和可溶性糖的含量则有不同程度的降低,叶绿素含量大大减少;异养有利于亚麻酸的积累;在混养条件下,光照使可溶性蛋白、可溶性糖和叶绿素的含量增加,其强度对细胞的生化成分有影响．     

光密度法测定蛋白核小球藻生物量

目的修正传统光密度测定微藻生物量的方法。方法通过扫描并比较蛋白核小球藻藻液和总色素提取物在200～800nm范围内的吸光值,确定最佳波长以修正传统光密度法测定波长,绘制标准曲线来间接测定蛋白核小球藻的生物量。比较修正前后光密度法测定蛋白核小球藻生物量的精确性。结果 517nm下对应的吸光值与蛋白核小球藻的生物量有显著的线性关系。采用修正后光密度法测定干重量具有良好的线性关系:Y=0.257 8X-0.005 1(R2=0.995 6),相比传统光密度法具有更好的相关性;采用修正后光密度法测定细胞密度具有良好的线性关系:D=2 320.4X+0.030 6(R2=0.999 3),相比传统光密度法具有更好的相关性;修正后光密度法与干重法实时测定的蛋白核小球藻生物量结果基本一致,而传统光密度法与干重法具有一定的偏差。结论采用517nm修正传统光密度法测定波长,有效消除了色素干扰带来的误差,可以作为蛋白核小球藻生物量测定的特征波长。     

小球藻培养条件的研究

对影响小球藻生长的NaHCO3、NaNO3、KH2PO4、维生素等4种主要营养因素进行了优化,获得了以海水为基础的优化培养基配方:NaHCO30.10g/L,NaNO30.225g/L,KH2PO40.005g/L,pH6.0.另外,适量添加土壤浸出液和维生素也会明显提高藻的产量.流加培养可以促进小球藻生物量的增加.     

Z-QS01菌株对小球藻的生态学效应及对UV-B辐射的响应

利用生态毒理学方法研究了小球藻共栖Z-QS01菌株的生态学效应及对UV-B辐射的响应.结果表明:Z-QS01菌株通过分泌化学物质实现自我行为调节和对小球藻的抑制效应,Z-QS01菌株的密度和分泌到培养液中的化学物质的浓度是启动调节机制的必要条件;UV-B辐射增强显著影响Z-QS01菌株的群感效应,随UV-B辐射剂量的增加,Z-QS01菌株对小球藻的抑制效应降低.实验数据可为水产养殖业生态防病提供参考,并为揭示藻菌间相互作用机制提供有价值的参考资料.