## 3 Results and Discussion
### Macronutrient Content  
The composition of the whole intact biomass of _C. reinhardtii_, _Spirulina_ and _Chlorella_ was analyzed and calculated as a percentage of dry weight (DW) (Figure 2). The moisture content of 1.1% for _C. reinhardtii_, 1.8% for _Spirulina_, and 1.88% for _Chlorella_ are within the range of the recommended limit of \(<\)10% for microalgae powder quality [5]. The protein content of _C. reinhardtii_ (46.9%) was slightly higher than that of _Chlorella_ (45.3%) and slightly lower than that of _Spirulina_ (50.4%), however, there were no significant differences between the three species (\(p\geq 0.05\)). Protein sources of \"not animal origin\" are generally divided into two groups, conventional such as legumes and non-conventional proteins such as single-cell protein including microalgae [15]. The protein contents of the three studied species were superior to that of high-protein plant foods such as soybean (37%) and milk (26%) [5]. [PERSON] et al. [39] reported that the protein content (calculated as a sum of amino acids) was 51.56% for _Spirulina_, and 39% for _Chlorella_, which is in close agreement with the values obtained in this study. Similarly, primary metabolism and the biomass composition of _C. reinhardtii_ as % of DW under different energy inputs were measured and it was found that the protein content ranged between 37 and 42% [40]. Figure 1: **(A)** Growth curve of _C. reinhardtii_ population grown in mixotrophic condition and measured using either a haemocytometer or spectrophotometer. Data representative of triplicate measurements (SD = 3). **(B)** TEM images of _C. reinhardtii_ grown in TAP and imaged at different time and conditions, a to c are the images of the 14 days old cells while d to f are the images of the 30 days old cells. Letters in blue inside the images refer to the following: P: Pyrenoid; LB: Lipid Bodies; S: Starch granule; TM: Phylakoid Membrane; E: Eyespots; G: Golgi bodies. Likewise, differences in the basic composition of _C. reinhardtii_ under different growth conditions, where the protein content under mixotrophic growing system reached 38.1% DW was reported [41]. The ash content of the three microalgae species in this study varied significantly. Ash content in microalgae is directly correlated with the concentration of inorganic compounds and salts in the water environment, where the microalgae were grown [8]. On a dry weight basis, _C. reinhardtii_ exhibited the lowest ash content (4.8%), followed by _Chlorella_ (9.3%) and _Spirulina_ (11.4%). The three values are well situated within the wide range of 8-40% ash content observed in microalgae [42]. The ash contents of the three species were lower than the maximum value allowed in algal products sold in the USA (45% DW), and were comparable with that of land vegetables, ranging between 5-10% DW [43]. The lower ash content in _C. reinhardtii_ may help to explain its relatively high content of lipids and pigments (chlorophyll and carotenoids) compared with the commercial species _Chlorella_ and _Spirulina_. In Figure 2, _C. reinhardtii_ showed a lipid content of 24.7% DW, which is higher than that of _Chlorella_ (16.1%) and _Spirulina_ (14.1%). Lipid content varies even among the same microalgae species and is highly affected by the growing parameters, more specifically the growing stress conditions. Numerous studies have been conducted to boost the total lipid level in _C. reinhardtii_ by applying different techniques of cell stressing. Reducing the nitrogen content was one of the most common stressing techniques which increased neutral lipid accumulation, as TAG (triacylglycerollycerol) droplets (from \(<\)1 ug up to 11 ug per million cells DW basis), accompanied with reduced photosynthetic efficiency and decreased growth. The stressing technique was extensively studied to boost TAG content for biofuel production from microalgae [44]. _C. reinhardtii_ had lower carbohydrate content compared with either _Spirulina_ or _Chlorella_ products (Figure 2).