High Light Stress Regimen on Dunaliella Salina Strains For Carotenoids Induction

Abstract

aim of this study was to select the most appropriate high light stress regimen for culturing D. salina strains to produce economically viable high concentrations of carotene. Materials and methods Dunaliella salina strains and experimental design Three Dunaliella salina strains were grown and maintained in modified natural seawater medium 1.5M (MD4) [19]. The medium contained NPK* 0.1g/l, MgSO 4 1.86g/l, EDTA 0.00876g/l, FeCl 3 0.00049g/l, MnCl 2 0.00189g/l, NaCl 1.5M, NaHCO 3 50mM. PH was adjusted to 7.5 ± 0.5. (* N-P-K (30-15-10): 30% N, 15% P2O5, 10% K2O, 0.05% Mg, 0.05% Ca, 0.01% B, 0.05% Zn, 0.05% Cu, 0.05% Fe, 0.025% Mn, 0.005% Mo.). 30 ml of algal culture was grown in 50 ml-flasks with initial cell concentration of 1x10 5 cells/ml. Samples were manually mixed daily. Each strain was grown with three replicates. Cultures were maintained at room temperature and light intensity of 50 µmol.photons/m 2 /s (measured by Digital light intensity meter, LITEcheck) for the first 10 days. At day 11, samples were stressed by maintaining high light Abstract The microalgae Dunaliella salina is the richest source of commercial β-carotene known to man. This natural compound has been proven invaluable in medicine, industry and other fields of science, due to its provitamin A activity and potential disease suppression, as well as usage as a supplement for food and animal feed including as additive to food and cosmetics. However, β-carotene content in Dunaliella cells depends heavily on growth conditions and nutrient parameters. A set of experiments was conducted to determine the optimum high light stress regimen for Dunaliella salina to achieve the highest carotenoids induction. Three D. salina strains (D. salina CCAP 19/18, D. salina A9 and D. bardawil) were cultured in MD4 1.5M medium under stress condition at different regimens for a period of 26 days. Following the first phase of exponential growth, 3 different growth cycles were tested: a cycle of three-day at 800 µmol.photons/m 2 /s and one day at 50 µmol.photons/ m 2 /s, a cycle of one day at 800 µmol.photons/m 2 /s and three-day at 50 µmol.photons/m 2 /s and finally an all-time stress at 800 µmol.photons/m 2 /s. Total carotenoids were analyzed over the experimental period, including the antioxidant capacities and total phenolic contents of the algal carotenoid extract were simultaneously evaluated. Result revealed that all three D. salina strains produced the highest concentration of total carotene under the all-time stress regimen of 800 µmol.photons/ m 2 /s, and D. salina CCAP had higher total carotenoid content than D. salina A9 and D. bardawil in all stress conditions. This study could surely serve as the basis for scaling up this process to industrial-level applications, which will undoubtedly require further investigation and evaluation of the extraction and testing procedures.