# Caroenoid Production from Microalgae: Biosynthesis, Salinity Responses and Novel Biotechnologies
## 4 Potential Applications of Internet of Things (IoT) in Carotenoids Production  
The Internet of Things (IoT) is a huge ecosystem that connects things, machines and humans, anytime and anywhere. As the third wave of the world information industry, the IoT has attracted thriving research interest from various fields, such as the food supply chain [93], healthcare applications [94] and precision agriculture [95]. The number of IoT devices worldwide is predicted to reach 75 billion by 2025 [93]. Considering its successful experiences in agriculture and its advantages as a real-time, efficient and intelligent comprehensive data system of works, the IoT also shows competitiveness in microalgae biorefinery [96]. Microalgae biorefinery can be divided into two consecutive categories, the upstream processing and downstream processing [97]. The upstream processing mainly focuses on the high-density cultivation of selected microalgae and the regulation and optimization of the cultivation process, such as choosing the suitable trophic mode and light conditions. The downstream process mainly includes the harvest of microalgae, the separation and extraction of key products and subsequent processing to make microalgae-derived products. The IoT, as an ubiquitous, huge network, can be perfectly combined with traditional biotechnologies in microalgae biorefinery [96]. As shown in Figure 4, both upstream and downstream events are connected and collected, and all information will then be processed by the IoT platform. Then, how can the IoT be applied in the production of microalgae-derived carotenoids? \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Stress Conditions** & **Microalgae** & **Carotenoids** & **Fold Change** & **Ref.** \\ \hline
100-500 mM NaCl (Two-stage) & _Caccomyza anubensis_ & Lutein & 0.47-fold & [89] \\
200 mM NaCl & C. _zafingiensis_ CCAP 211/14 & Astaxanthin & 1.23-fold & [88] \\
36.27 g/L NaCl & _Tischrysis lutea_ & Fuccaxanthin & – & [64] \\
2\% NaCl (\(w/v\)) & _Chromochloris zafingiensis bkt1_ & Lutein & 1.38-fold & \\  & & \(\beta\)-carotene & 0.36-fold & \\ High light + NaCl & _Chromochloris zafingiensis_ & Astaxanthin & 7.53-fold & [70] \\ LA + NaCl (20\%) & _Chorella sonvitamin_ & Astaxanthin & 1.25-fold & [92] \\ GABA + high light + NaCl & _Haematococcus phytailis_ & Astaxanthin & 3.24-fold & [90] \\ MT+ N-starvation + NaCl & _Haematococcus phytailis_ & Astaxanthin & 1.20-fold & [91] \\ TiO\({}_{2}\) + N-starvation + NaCl & _Colsatrella sp._ & Zeaxanthin & 0.51-fold & [42] \\  & & Astaxanthin & 1.16-fold & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Salt treatment and salinity-combined conditions for carotenoids production. For the upstream processing of carotenoid production, sensors are indispensable for data monitoring. Traditional detection techniques (such as measurement of biomass, cell size, etc.) are time-consuming, prone to causing culture contamination and cannot get data in time. In comparison, online sensors can monitor microalgae growth to gain real-time data, calculate unmeasured variables and even predict growth models. For example, _H. pluvialis_ is relatively sensitive to culture environment; its growth and cell composition can go far away from expectations without careful tuning. Possible contamination during sampling can disturb its growth. In addition, nutrient deficiency could drive it into a cyst structure and cause it to begin accumulating astaxanthin and other secondary metabolites [10]. In this case, innovative online sensors can monitor its growth in several aspects. Optical density (OD) sensors [98; 99] can determine real-time biomass and dissolved oxygen (DO), CO\({}_{2}\) sensors [100] can screen metabolic activity, pH sensors and nitrate and phosphorous sensors [101] can guarantee a suitable environment and nutrient sufficiency; these can all be applied to ensure high-density cultivation of _H. pluvialis_. Moreover, the IoT can also act as the base of a decision support system.