# Caroenoid Production from Microalgae: Biosynthesis, Salinity Responses and Novel Biotechnologies
## 2 Health-Promoting Carotenoids from Microalgae and Their Biofunctions
### Health-Promoting Carotenoids and Their Production from Microalgae  
#### 2.2.1 Lutein  
Lutein, (3\(R\), 3\(R\), 6_R_)-\(\beta\), \(\varepsilon\)-carotene-3, 3_\({}^{\prime}\)-diol, is a natural antioxidant and has drawn interest for its health-promoting functions. Human metabolism cannot synthesize lutein,  
Figure 1: Biosynthesis pathways of carotenoids in microalgae and their chemical structures. MEP: methylerythnitol phosphate; IPP: isopentenyl pyrophosphate; DMAPP: dimethylallyl diphosphate; GPPS: geranyl diphosphate synthase; GGPPS: geranyl pyrophosphate synthase; GGPPS: geranyl pyrophosphate synthase; GGPP: geranyl pyrophosphate; PSY: phytoene synthase; Z-ISO: \(\zeta\)-carotene isomerase; ZDS: \(\zeta\)-carotene desaturase; CrtlSO: caroten isomerase; LCYE: lycopene epsilon cyclase; CY97A: cytochrome P450 beta hydroxylase; CY97G: cytochrome P450 epsilon hydroxylase; LCYB: lycopene \(\beta\)-cyclase; BKT: \(\beta\)-carotene ketolase; CHYB: \(\beta\)-carotene hydroxylase. and lutein uptake in a suggested dose (6 mg day\({}^{-1}\)) has been proved to be beneficial for human health. Lutein has potentials in free radical scavenging for skin health and can also prevent age-related macular degeneration (AMD) and Alzheimer's Disease (AD) [3; 17]. Absorbed lutein can accumulate in human retina, filter blue light and, thus, protect eyesight. Biofunctional carotenoids and their natural sources, biofunctions and recommended doses are listed in Table 1.  
Orange-yellow fruits like mango, broccoli and other green leafy vegetables are dietary sources of lutein [22].The margold flower is the main source of natural lutein and lutein esters. Lutein contents in different species of margold petals range from 17 to 570 mg/100 g [23]. However, there are some drawbacks of this source, such as mandatory harvesting in specific seasons and time-consuming petal separation. Other sources containing lutein also have such disadvantages as low concentration (corn residues, leafy green vegetables) and low bioavailability (egg yolk, crustaceans) [24]. The production of lutein from microalgae may avoid these troubles. Microalgae can accumulate considerable biomass concentrations and accumulate lutein under suitable culture conditions. As a primary xanthophyll carotenoid, lutein is an antenna pigment in  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Carotenoids** & **Natural Sources** & **Biofunctions** & **Recommended Dose** & **Ref. ** \\ \hline \hline \multirow{4}{*}{**Lutein**} & \multirow{4}{*}{Marigold flower *; Yolk; Broccoli; Mracalgae Orange-yellow freituits; Leafy green vegetables; Anti-inflammatory Anti-inflammatory Anti-  
the light-harvesting complex (LHC) of microalgal photosynthetic apparatus. When light intensity is too high, lutein can reduce oxidative damage by non-photochemical quenching (NPQ) [25]. Thus, illumination is a key environmental factor for lutein accumulation. Compared with marigold-originated lutein, lutein in microalgae exists in free form. The feasibility and economic competitiveness of using microalgae to replace the marigold flower to produce lutein has been widely discussed [23; 24], including harvesting cost, extraction and processing methods and bioavailability analysis. Up until now, many microalgae subgenera have been investigated for lutein production, such as _Scenedesmus_, _Chlorella_, _Cocomvza_, _Parachlorella_ and _Tetraselmis_[25]. To achieve both high content and productivity of carotenoid from microalgae, various cultivation factors are globally considered, including trophic mode, carbon source, fed-batch, semi-continuous operation, light intensities and light/dark cycles, etc. [25]. Mixotrophic is popular in lutein production from various microalgae capable of glucose uptake, such as _Chlorella minutissima_[26], _Chlorella sorokiniana_ MB-1-M12 [27] and _Chlorella_ sp. GY-H4 [28]. The lutein production of _Chlorella_ sp. GY-H4 under 20 g/L glucose (10.5 mg/L/day, 63 mg/L) was higher than that under 10 g/L glucose (7.3 mg/L/day, 44 mg/L) [28].