Adaptation of autotrophic to heterotrophic culture of Porphyridium purpureum (Bory) KM Drew & R.Ross: characterization of biomass and production of exopolysaccharides

Microalgae are successfully adapted to different environments where they metabolize inorganic and, in some cases, organic compounds. The modification of culture conditions can induce the synthesis of exopolysaccharides with potential health benefits. This study aims to adapt the autotrophic culture of the red alga Porphyridium purpureum to a heterotrophic culture in order to compare the biochemical composition of biomass and the production of exopolysaccharides (EPS). The adaptation of autotrophic to heterotrophic culture was carried out by progressively reducing the photoperiod and adding glucose. EPS extraction and purification were carried out. EPS were characterized by Fourier transform infrared spectroscopy and gas chromatography-mass spectrometry. The antioxidant capacity of both biomasses was analyzed by the 2,2 '-azino-bis (3- ethylbenzothiazoline-6-sulphonic acid) (ABTS) method and 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. Results for both biomass and EPS showed significant differences in biochemical composition and antioxidant activity under the two growing conditions. Furthermore, the heterotrophic EPS (HT-EPS) seems to favor the accumulation of glucuronic acid. Our results are the first adaptation from autotrophic to heterotrophic culture of P. purpureum. These trophic variations show that P. purpureum can adapt to heterotrophic culture and present interesting differences in its biochemical composition, being an alternative in the increase of metabolites, mainly carbon compounds, of interest to the industry.