Utjecaj selena na akumulaciju lipida u morskoj mikroalgi Dunaliella tertiolecta tijekom različitih načina kultivacije

doctoral thesis

• Title (english): Influence of selenium on lipid accumulation in the marine microalgae Dunaliella tertiolecta during different cultivation modes
• Author: Maja Galić Perečinec
• Mentor: Mirela Ivančić Šantek (mentor)
• Committee member: Blaženka Kos (predsjednik povjerenstva)
• Committee member: Ivana Radojčić Redovniković (član povjerenstva)
• Granter: University of Zagreb; Faculty of Food Technology and Biotechnology; (Department of Biochemical Engineering); (Laboratory for Biochemical Engineering, Industrial Microbiology and Malting and Brewing Technology); Zagreb
• Defense date and country: 2023, Croatia
• Scientific / art field, discipline and subdiscipline: BIOTECHNICAL SCIENCES; Biotechnology
• Universal decimal classification (UDC): 60 - Biotechnology. Genetic engineering. Products of cloning

Abstract

Mikroalge imaju široku primjenu u proizvodnji biomase i biološki aktivnih spojeva. Glavni istraživački ciljevi bili su: utvrditi učinak različitih koncentracija anorganskog oblika selena (natrijevog selenita) na brzinu rasta, fotosintetsku aktivnost, razinu oksidativnog stresa i akumulaciju neutralnih lipida u morskoj mikroalgi D. tertiolecta, istražiti učinak selenita u hranjivoj podlozi na akumulaciju lipida tijekom jednostupanjskog i dvostupanjskog uzgoja mikroalgi te ispitati izvedivost povećanja uzgoja i sinteze lipida s mikroalgama u laboratorijskom fotobioreaktoru uz dodatak selenita. Najveće vrijednosti optičke gustoće (OD₆₈₀=0,67) i gustoće stanica (43,11×10⁵ stanica mLˉ¹) postignute su tijekom 10. dana dvostupanjskog uzgoja u laboratorijskom fotobioreaktoru u podlozi obogaćenoj sa 20,00 mg Lˉ¹ selenita. Izlaganje mikroalge D. tertiolecta povišenim koncentracijama selenita (20,00 i 40,00 mg Lˉ¹) rezultiralo je povećanom koncentracijom malondialdehida (MDA) i drugih spojeva reaktivnih s tiobarbiturnom kiselinom (TBARS), što ukazuje na peroksidaciju lipida u stanicama mikroalgi. I u manjem (100 mL) i u većem mjerilu (2 L) uzgoja, najveće povećanje udjela neutralnih lipida zabilježeno je 14. dan dvostupanjskog uzgoja u kulturi mikroalgi koja je sadržavala 20,00 mg Lˉ¹ selenita. Tijekom uzgoja u laboratorijskom fotobioreaktoru najveći udio neutralnih lipida zabilježen je 11. dana uzgoja na 20,00 mg Lˉ¹ selenita te je bio 27,67 puta veći u odnosu na najveći udio lipida dobiven tijekom uzgoja u manjem mjerilu (100 mL). Usporedbom sastava masnih kiselina zabilježeno je značajno povećanje udjela palmitinske kiseline (C16:0) i oleinske kiseline (C18:1 cis 9) što je povoljno za proizvodnju biodizela. Također, analiza sastava masnih kiselina pokazala je prisutnost različitih masnih kiselina važnih u kontekstu proizvodnje višestruko nezasićenih masnih kiselina (palmitoleinska (C16:1 cis 9), linoleaidinska (C18:2 trans 9, 12), linolenska (C18:2 cis 9, 12) i γ-linolenska kiselina (C18:3 cis 6, 9, 12)). Uspoređujući izračunate vrijednosti četiri bitna fizikalna svojstva biodizela (cetanski broj (Φb), kinematička viskoznost (ηb), gustoća (ρb) i viša kalorična vrijednost (δb)) s vrijednostima standarda (ASTM D6751 i EN 14214) zaključeno je da biodizel proizveden transesterifikacijom lipida biomase mikroalgi D.tertiolecta uzgajanih pri različitim koncentracijama selenita zadovoljava sve zahtijeve standarda za proizvodnju biodizela. Dodavanje selenita u hranjivi medij mikroalge D. tertiolecta predstavlja potencijalnu strategiju za povećanje prinosa neutralnih lipida te poboljšanje potencijala uporabe lipida mikroalge D. tertiolecta za proizvodnju biodizela.

Abstract (english)

Microalgae have a wide range of applications in biomass production and the production of bioactive compounds. The main research objectives were to determine the effect of different concentrations of inorganic selenium (sodium selenite) on the growth rate, photosynthetic activity, oxidative stress levels, and neutral lipid accumulation in the marine microalga D. tertiolecta, investigate the effect of selenite in the nutrient medium on lipid accumulation during one-stage and two-stage microalgae cultivation, and examine the feasibility of increasing microalgal growth and lipid synthesis in a laboratory photobioreactor with the addition of selenite. The highest values of optical density (OD₆₈₀=0.67) and cell density (43.11×10⁵ cells mLˉ¹) were achieved on the 10th day of two-stage cultivation in a laboratory photobioreactor in a medium enriched with 20.00 mg Lˉ¹ of selenite. Exposure of the microalga D. tertiolecta to elevated concentrations of selenite (20.00 and 40.00 mg Lˉ¹) resulted in an increased concentration of malondialdehyde (MDA) and other thiobarbituric acid reactive substances (TBARS), indicating lipid peroxidation in microalgal cells. In both small (100 mL) and large-scale (2 L) cultivation, the highest increase in neutral lipid content was recorded on the 14th day of two-stage cultivation in a microalgal culture containing 20.00 mg Lˉ¹ of selenite. During cultivation in the laboratory photobioreactor, the highest neutral lipid content was recorded on the 11th day of cultivation with 20.00 mg L-1 of selenite, and it was 27.67 times higher than the highest lipid content obtained during microalgal cultivation on a smaller scale (100 mL). Comparison of the fatty acid composition showed a significant increase in the proportion of palmitic (C16:0) and oleic acid (C18:1 cis 9), which is favorable for biodiesel production. Additionally, the fatty acid composition analysis revealed the presence of various fatty acids important for the production of polyunsaturated fatty acids (palmitoleic (C16:1 cis 9), linoleaidic (C18:2 trans 9, 12), linolenic (C18:2 cis 9, 12), and γ-linolenic acid (C18:3 cis 6, 9, 12)). Comparing the calculated values of four essential physical properties of biodiesel (cetane number (Φb), kinematic viscosity (ηb), density (ρb), and higher heating value (δb)) with standard values (ASTM D6751 and EN 14214), it was concluded that biodiesel produced by transesterification of microalgal biomass lipids grown at different concentrations of selenite meets all the requirements for biodiesel production standards. Adding selenite to the nutrient medium of the microalga D. tertiolecta represents a potential strategy to increase the yield of neutral lipids and improve the potential use of D. tertiolecta microalgal lipids for biodiesel production.

• Keywords: mikroalge; D. tertiolecta; pigmenti; oksidativni stres; karotenoidi; lipidi; fotobioreaktor
• Keywords (english): Microalgae; D. tertiolecta; Oxidative stress; Carotenoids; Lipids; Photobioreactor
• Language: croatian
• URN:NBN: urn:nbn:hr:159:990179
• Promotion: 2023
• Study programme: Title: Postgraduate PhD Study in Nutrition; Study programme type: university; Study level: postgraduate; Academic / professional title: doktor/doktorica znanosti, područje biotehničkih znanosti, polje nutricionizam (doktor/doktorica znanosti, područje biotehničkih znanosti, polje nutricionizam)
• Type of resource: Text
• Extent: 226 str. ; 30 cm
• File origin: Born digital
• Access conditions: Open access
• Created on: 2023-09-25 12:29:32