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- Green approach for the valorization of microalgae Tetradesmus obliquusPublication . Gouveia, Luisa; Jazic, Jelena Molnar; Ferreira, Alice; Maletic, Snezana; Cvetkovic, Dragoljub; Vidovic, Senka; Vladic, JelenaABSTRACT: The main goal of this study was to develop an efficient, green approach for the valorization of Tetradesmus obliquus biomass, with zero waste. This microalga was selected because it is widespread, resistant, easy for cultivation, and fast-growing. In the first step, supercritical carbon dioxide (ScCO2) extraction followed by rapid gas decompression was used for the extraction of biomass. The following step was to apply ultrasound-assisted (UA), microwave-assisted (MA), and subcritical water (SW) extraction on the ScCO2-treated biomass to determine the most efficient processing technology. SW demonstrated to be a superior technique over MW and UA with regard to extraction yield and antioxidant content. Moreover, the chemical and microbiological profiles of SW extracts were determined to evaluate their potential and safety. In addition, to create a procedure with zero waste, the solid waste after SW extraction (residue) was analyzed. The organic profile of extracts and residues contained compounds that belong to groups of aliphatic saturated hydrocarbons, aliphatic unsaturated hydrocarbons, alkylated hydrocarbons, ketones, phenols, and esters. Furthermore, these compounds can be applied in different industries including the pharmaceutical and cosmetic industries. Additionally, the content of metals in residues indicated that this material can be used as animal feed and in agriculture. Finally, a complete reduction of microorganisms present in the initial biomass was obtained for the extracts and residues, indicating their safety.
- Valorisation of microalga Tetradesmus obliquus grown in brewery wastewater using subcritical water extraction towards zero wastePublication . Ferreira, Alice; Jazic, Jelena Molnar; Gouveia, Luisa; Maletic, Snezana; Tomic, Milan; Agbaba, Jasmina; Vladic, JelenaABSTRACT: In this study, green technology was applied for extraction of compounds from wastewater-grown microalga biomass with the final goal of obtaining microbiologically safe products within a sustainable biorefinery process with zero waste. Tetradesmus obliquus biomass resulting from brewery wastewater treatment, with (To-CO2) and without CO2 supplementation (To), was submitted to subcritical water extraction (SWE) at temperatures 120-220 degrees C for 10 min. The impact of the different SWE conditions in the obtained liquid extracts and solid residues were investigated for metal content and chemical and microbiological profiles. Gas chromatography-mass spectrometry analysis indicated that of T. obliquus extracts and residues are valuable sources of aliphatic saturated, unsaturated, and alkylated (mostly methylated) hydrocarbons, phenols, esters, and ketones. Polyphenolic content and antioxidant activity were enhanced approximately 4 times by increasing the temperature from 120 to 220 degrees C. Also, the content of polyphenols doubled when T. obliquus was supplemented with CO2 for all the tested temperatures (To: 0.249-1.016 mg GAE mL(-1); To-CO2: 0.437 - 1.767 mg GAE mL(-1)). The microbiological analysis determined that liquid extracts and residues represent safe sources of bioactive components that can be used in different industries. In addition, the lower content of heavy metals in residues suggests the possibility of using the solid waste as animal feed or soil conditioner in agricultural applications.