Effect of UV radiation or titanium dioxide on polyphenol and lipid contents of Arthrospira (Spirulina) platensis

Phenolics and lipids of Arthrospira (Spirulina) platensis are important compounds with attractive properties. The influence of two oxidative stress conditions (UV irradiation and TiO2 concentration) on the production of these added-value compounds was investigated. UV and TiO2 stresses were shown not to influence the final concentration of biomass that resulted to be 4.83 and 5.08 g L− 1, respectively. Compared to the control run, total polyphenol yield decreased by 7.5, 24.1 and 23.1% after UV exposure for 3, 6 and 9 h, respectively, whereas in the presence of 0.10, 0.25 and 0.50 g L− 1 of TiO2 such a yield increased by 8.4, 7.0 and 7.3%, respectively. However, the treatment with 9 h of UV stress led to a lipid content increase of 29.5%, but with a reduction of the FAME fraction (67.3%). While the TiO2 stress lead to a substantial decrease of total lipid fraction. These results on the whole suggest that UV irradiation could be usefully exploited to increase the lipid content of microalgae or cyanobacteria for different applications in bioenergy production (e.g. combustion, gasification and pyrolysis), while the increased phenolic content induced by the oxidative stress with TiO2 may be of some interest in both the pharmaceutical and cosmetic sectors.