# Development of an Organic Culture Medium for Autotrophic Production of _Chlorella vulgaris_ Biomass
## 3 Results and Discussion
### Evaluation of Organic C. vulgaris Biomass  
In order to have an \"organic\" certification, the final product needs to meet the requirements of EU Regulation 2018/848 on organic production and labelling of organic products. Furthermore, its nutritional composition should be appealing to buyers in terms of food quality standards when compared with non-organic products, and above all, ensure food safety requirements for the consumer. Therefore, the biochemical composition of biomass produced in the tubular photobioreactors using the optimized organic culture medium and the synthetic medium was analysed (Table 4). The mean protein content of _C. vulgaris_ grown in organic and synthetic media was 57.2 and 58.6 g 100 g\({}^{-1}\), respectively. These values are consistent with the values reported by [PERSON] et al. (2018), but considerably higher than those reported by [PERSON] et al. (2018) and [PERSON] et al. (2018) in which _C. vulgaris_ biomass presented lower protein contents (38.0-47.82 g 100 g\({}^{-1}\)). Proteins have a special role in human nutrition due to the presence of essential amino acids, which are building blocks for proteins and, thus, for growth, cell metabolism, and tissue maintenance. This result is highly significant, as the demand for alternatives to animal protein is on the rise, in particular, due to the growing trend of consumers choosing vegan and vegetarian diets. The mean values of total lipids obtained in the biomass grown in organic medium (9.4 g 100 g\({}^{-1}\)) were slightly lower than those obtained with the synthetic culture medium (11.0 g 100 g\({}^{-1}\)). The lipid content here reported for biomass grown using both media is similar to the values previously reported in the literature for _C. vulgaris_([PERSON] et al., 2018). \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Growth Media** & \multicolumn{3}{c}{**“Organic”**} & \multicolumn{3}{c}{**“Synthetic”**} \\ \cline{2-7}
**Contents** & **Min** & **Mean** & **Max** & **Min** & **Mean** & **Max** \\ \hline
**Proximate Composition** & & & & & & \\ Protein (g 100 g\({}^{-1}\)) & 56.8 & 57.2 & 57.6 & 55.2 & 58.6 & 61.9 \\ Lipids (g 100 g\({}^{-1}\)) & 8.6 & 9.4 & 10.1 & 10.5 & 11.0 & 11.5 \\ Carbohydrates (g 100 g\({}^{-1}\)) & 3.9 & 4.4 & 4.8 & 0.5 & 1.5 & 2.1 \\ Dietary fibres (g 100 g\({}^{-1}\)) & 16.9 & 16.9 & 16.9 & 14.2 & 15.5 & 16.7 \\ Ash (g 100 g\({}^{-1}\)) & 9.1 & 9.2 & 9.3 & 8.3 & 10.8 & 13.3 \\ Moisture (g 100 g\({}^{-1}\)) & 2.3 & 3.0 & 3.7 & 2.5 & 2.8 & 3.0 \\ Energy (JJ 100 g\({}^{-1}\)) & 1499 & 1529 & 1559 & 1510 & 1551 & 1591 \\ Energy (J kcal 100 g\({}^{-1}\)) & 357 & 365 & 372 & 361 & 370 & 379 \\
**Pigments (mg g\({}^{-1}\))** & & & & & & \\ Chlorophyll \(a\) and \(b\) & 8.1 & 12.6 & 17.1 & 9.9 & 10.7 & 11.5 \\ Pheophytin \(a\) and \(b\) & 7.7 & 10.1 & 12.4 & 12.4 & 13.9 & 15.3 \\ Total carotenoids & 4.9 & 6.2 & 7.5 & 4.7 & 5.0 & 5.4 \\
**Heavy Metals (mg kg\({}^{-1}\))** & & & & & & \\ Tin & 2 & 2.5 & 3 & & \(<\)2(LOD) & \\ Lead & 0.08 & 0.09 & 0.10 & 0.10 & 0.12 & 0.13 \\ Cadmium & & \(<\)0.05 (LOD) & & & \(<\)0.05(LOD) & \\ Arsenic & & \(<\)0.10 (LOD) & & 0.16 & 0.21 & 0.26 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Analytical composition of Chlorella vulgaris dried biomass grown in “synthetic” and “organic” growth media in 10 m\({}^{3}\) tubular photobioreactors. The results represent the minimum, mean, and maximum values for two individual biological replicates. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**PBR** & \begin{tabular}{c} **Biomass Productivity** \\ **(g L\({}^{-1}\) d\({}^{-1}\))** \\ \end{tabular} & \
\begin{tabular}{c} **Specific Growth Rate** \\ **(d\({}^{-1}\))** \\ \end{tabular} &
\begin{tabular}{c} **Final Dry Weight** \\ **(g L\({}^{-1}\))** \\ \end{tabular} \\ \hline PBR 1 & 0.024 & 0.025 & 1.13 \\ PBR 2 & 0.021 & 0.024 & 1.02 \\ PBR 3 & 0.022 & 0.028 & 0.96 \\ Average & 0.023 \(\pm\) 0.001 & 0.026 \(\pm\) 0.002 & 1.04 \(\pm\) 0.09 \\ \hline \hline \end{tabular}
\end{table}