# Antioxidant Production in _Dunaliella_
## 3 Cultivation Conditions
_Dunaliella_ strains can adapt to grow under quite different nutrients conditions, which demonstrates the diversity of these strains [112; 113; 114; 115]. The essential photoautotrophic growth parameters of microalgae (_Dunaliella_) are shown in Figure 3. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Characteristics** & **Photo-Autotrophic** & **Heterotrophic** & **Mixotrophic** \\ \hline Bioreactor’s surface tovolume & & & \\ ratio (m\({}^{2}\)/m\({}^{3}\)) & High & Low & High \\ \hline Sterility & Usually sanitised & Sterility required & Not required \\ \hline Contamination risk & Low & High & Medium \\ \hline Harvesting cost & High due to the low density of biomass & Low due to high biomass & Low due to high biomass \\  & biomass & concentration & concentration \\ \hline Bioreactor set up cost (per unit & & & \\ of volume) & High & Low & High \\ \hline Bioreactor operation cost (per & & & \\ kg of biomass) & Low & Medium & High \\ \hline Scale-up & Design optimisation required & Easy & Design optimisation required \\ \hline Efficiency in wastewater & & & \\ treatment & Low & High & High \\ \hline Growth rate & Low & Medium & High \\ \hline Biomass density (g L\({}^{-1}\)) & Low & Medium & High \\ \hline Lipids (\%) & Low & High & High \\ \hline Proteins (\%) & High & Low & Medium \\ \hline Carbohydrates (\%) & Low & High & Low \\ \hline Chlorophyll and \(\beta\)-carotene & & & \\ (\%) & High & Low & Medium \\ \hline Lutein (\%) & Medium & High & High \\ \hline \hline \end{tabular}
\end{table} 
Table 3: _Cont._Using available technologies, _Dunaliella_ biomass production costs are approximately US $4.92 kg\({}^{-1}\), which, for biodiesel production, is exceptionally high. Production costs could be reduced (US $3.05 kg\({}^{-1}\)) if biomass was produced using waste water as a nutrient source [116]. A biomass production costs of US$ 4.92 kg\({}^{-1}\) would be acceptable if biomass was used for the production of high-value products (processed biomass value, US $123 kg\({}^{-1}\)) [117]; \(\beta\)-carotene (from _Dunaliella_ spp.) and astaxanthin (from _Haematococcus_ spp.) command a market value of $100-1000 kg\({}^{-1}\)[117]. Moreover, the demand for astaxanthin, \(\beta\)-carotene and lutein is now emerging in the market. The global carotenoid market was valued at $1.3 billion in 2017 and is projected to reach $1.8 billion by 2022 [7]. Other high-value compounds such as antioxidant enzymes could make _Dunaliella_ biotechnologies economically profitable. The current biomass productivity of _D. salina_ lies between 0.75 g m\({}^{-2}\) d\({}^{-1}\) and 3.0 g m\({}^{-2}\) d\({}^{-1}\) (ash-free dry weight, AFDW) [118], depending on seasonality and other cultivation factors. Variation of growth parameters disturbs intracellular metabolism via photosynthesis and photorespiration, which results in an imbalance between the generation and detoxification of ROS, ultimately stimulating enzymatic and non-enzymatic antioxidant responses. Therefore, modifications of cultivation factors may enhance antioxidants levels, making _Dunaliella_ a competitive candidate for antioxidant (enzyme and non-enzyme) production.