The Production of α-Tocopherol, Sterols and Fatty Acids by Three Marine Microalgae

Abstract

A comparative study of the production of $α$-tocopherol, sterols and fatty acids by Tetraselmis suecica, Isochrysis galbana and Chlorella sp. was done. The level of these compounds was determined in the exponential, stationary and decay phases of microalgae cultures kept at 18 {\textdegree}C and 24 h light. The highest level of $α$-tocopherol was attained in the decay phase of I. galbana and T. suecica (ca. 350 {\textmu}g/g of freeze-dried material) but for Chlorella sp. (ca. 180 {\textmu}g/g of freeze-dried material) the maximum level was achieved in the stationary phase. Stigmasterol, sitosterol, campesterol, cholesterol and cycloartenol were identified. The level of these sterols, however, was very much dependent on species and growing stage. The highest levels of these sterols were recorded in I. galbana. Concerning $ω$3 fatty acids, linolenic acid (18:3$ω$3) was present at the highest level in Chlorella sp. and T. suecica. The maximum level attained in Chlorella sp. was 20% in the exponential phase whereas it was achieved (12%) in the decay phase in T. suecica. The level of eicosapentaenoic acid (20:5$ω$3) was particularly high (28%) in I. galbana. This microalgae presented also 6% of docosahexaenoic acid (22:6$ω$3) but only traces of this fatty acid were detected in Chlorella sp. and T. suecica. The production of these biomolecules was also studied at two different growing conditions - 26 {\textdegree}C/ 24 h light and 18 {\textdegree}C/ 16 h light. These changes in the growing conditions did not affect the production of tocopherol by Chlorella sp. but a reduction was observed in the other two species. The change of the photoperiod led to an increased production of $β$-sitosterol and stigmasterol in I. galbana but in the other two species a decrease of all sterols was recorded. The higher temperature caused also lower sterol levels. The changes in growing conditions were positive for the production of polyunsaturated fatty acids in Chlorella sp. However, its production by I. galbana and T. suecica was negatively affected.