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Research background. Microalgae represent an emergent sustainable source of bioactive compounds such as antioxidants, vitamins, minerals and polyunsaturated fatty acids that can ameliorate the nutritional characteristics of foods. The biochemical composition of microalgae could be modulated by varying the culture conditions to enhance the accumulation of biomolecules of interest. The aim of this work is to optimise the nutri-functional properties of two microalgae that can be used in food production. Experimental approach. Nannochloropsis gaditana L2 and Chlorella sp. SM1 were screened for growth, biochemical composition and radical scavenging activity employing four different growth media (algal, BG-11, f/2 and Conway) with different nutrient composition. The feasibility of using Chlorella sp. SM1 cultivated in BG-11 medium, in an under-investigated Mediterranean dairy product ricotta cheese and its effect on the sensory attributes was investigated. Additionally, Arthrospira platensis was used as reference in sensory analysis. Results and conclusions. Nitrate- and phosphate-rich media (BG-11 and algal) enhanced the biomass productivity. However, the highest lipid production (23.10 and 11.86 mg/(L·day) by strains SM1 and L2 respectively) and carbohydrate content (34.79 and 44.84% by SM1 and L2 respectively) were obtained with the nitrate-deficient f/2 medium. Regardless of the used medium, the lipid profile of Chlorella sp. SM1 and N. gaditana L2 remained adequate for different applications with >50% C16-18 as the main fatty acids. Significant increase in oleic acid (C18:1) content was recorded in response to nitrogen deficiency, being the highest in SM1 in f/2 medium (34%). Nitrogen deficiency was also found to enhance phenolic compound (expressed as gallic acid equivalents, 48.8 and 35.1 mg/g in SM1 and L2 respectively) and carotenoid contents (2.2 and 2.0 mg/g in SM1 and L2 respectively). Due to its interesting antioxidant potential, Chlorella sp. SM1 was used at different mass fractions (0.2, 1 and 1.5%) to enrich the ricotta cheese. The sample with 0.2% Chlorella sp. SM1 was found to give the most appreciated product. Novelty and scientific contribution. This study presents the production of an innovative ricotta cheese using Chlorella sp. as a functional ingredient, without altering the manufacturing procedure, while maintaining acceptable sensorial characteristics. The biochemical composition of the used strains varied depending on the culture medium composition, which enabled the accumulation of phytonutrients of interest., Pozadina istraživanja. Mikroalge su sve češći održivi izvor bioaktivnih spojeva, poput antioksidansa, vitamina, minerala i polinezasićenih masnih kiselina, kojima se mogu poboljšati nutritivna svojstva hrane. Biokemijski se sastav mikroalgi može izmijeniti promjenom sastava podloge za uzgoj, s ciljem povećanja prirasta željenih biomolekula. Svrha je ovoga rada bila optimirati hranjiva i funkcionalna svojstva dviju vrsta mikroalgi koje se mogu primijeniti u proizvodnji hrane. Eksperimentalni pristup. Analizirani su rast, biokemijski sastav te sposobnost uklanjanja slobodnih radikala mikroalgi Nannochloropsis gaditana L2 i Chlorella sp. SM1 uzgojenih u četiri podloge različitog sastava (hranjiva podloga za uzgoj algi, BG-11, f-2 i hranjiva podloga Conway). Ispitana je mogućnost primjene alge Chlorella sp. SM1 uzgojene u BG-11 podlozi u proizvodnji sira tipa ricotta, mediteranskog mliječnog proizvoda koji je slabo istražen, te njezinog utjecaja na senzorska svojstva sira. Uz to, mikroalga Arthrospira platensis upotrijebljena je za izradu kontrolnog uzorka za senzorsku analizu. Rezultati i zaključci. Proizvodnja se biomase povećala u podlogama bogatim nitratima i fosfatima (BG-11 i hranjiva podloga za uzgoj algi). Međutim, najveća proizvodnja lipida (dnevno 23,10 mg/L u soju SM1 i 11,86 mg/L u soju L2) i najveći udjel ugljikohidrata (34,79 % u soju SM1 i 44, 84 % u soju L2) postignuti su uzgojem u podlozi f/2 siromašnoj nitratima. Bez obzira na sastav podloge, sastav lipida u mikroalgama Chlorella sp. SM1 i N. gaditana L2, s više od 50 % C16-18 kao glavnim masnim kiselinama, bio je prikladan za različite primjene. Nedostatak dušika doveo je do znatnog povećanja udjela oleinske kiseline (C18:1), i to najviše u soju SM1 uzgojenom u podlozi f/2 (34 %). Također su opaženi povećani udjeli fenolnih spojeva (48,8 mg/L u soju SM1 i 35,1 mg/g u soju L2, izraženo kao ekvivalent galne kiseline) i karotenoida (2,2 mg/g u soju SM1 i 2,0 mg/g u soju L2). Zbog svog zanimljivog antioksidacijskog potencijala, mikroalga Chlorella sp. SM1 primijenjena je u različitim masenim udjelima (0,2; 1 i 1,5 %) za obogaćivanje sira tipa ricotta. Proizvod s najboljiim karakteristikama dobiven je s dodatkom 0,2 % ove mikroalge. Novina i znanstveni doprinos. U radu je prikazana proizvodnja novog sira tipa ricotta s dodatkom mikroalge Chlorella sp. kao funkcionalnim sastojkom, pri čemu se nije mijenjao postupak proizvodnje, a zadržane su prihvatljive senzorske značajke sira. Biokemijski je sastav korištenih sojeva mikroalgi ovisio o sastavu hranjive podloge, pa je time bilo moguće povećati proizvodnju željenih fitonutrijenata.