Design of experiment to increase lipid and pigment production in Chromochloris zofingiensis: lab and pilot scale cultivation

Microalgae are proving to be promising sustainable food sources of the future, characterised by high nutritional value with proven health benefits. Within this context, the eukaryotic microalgae Chromochloris zofingiensis is increasingly gaining the attention of the scientific community, as it exhibits several features that make its application for biotechnological purposes highly advantageous. These characteristics include rapid growth, trophic flexibility and simultaneous synthesis of high amounts of triglycerides and carotenoids, including the antioxidant ketocarotenoid astaxanthin, in response to stress conditions (e.g. nitrogen deprivation, osmotic stress). To increase lipid and carotenoid production, the combined effect of different stresses was tested by applying a Design of Experiment (DoE) approach on growth curves carried out in CellDEG, a high-density cultivation system. Chromochloris zofingiensis was then cultivated in a 200 L photobioreactor under photoautotrophic conditions following a two-stage cultivation strategy: a first phase where microalgae were grown under favourable conditions in order to obtain the highest biomass yield, followed by a second phase where stress was applied. In particular, two different stresses were analysed, namely nitrogen depletion and osmotic stress. Additionally, since nitrogen availability appeared to be one of the main variables influencing lipid and pigment productivity, further preliminary experiments were conducted in a continuous flat panel photobioreactor employing different nitrogen concentrations, while keeping incident light intensity, salt concentration and residence time constant.