## 4 Discussion
MCC41 presents high concentrations of palmitic acid, can grow under mixotrophic conditions, and fixes atmospheric nitrogen [36]. Thanks to these properties, they may represent excellent raw materials for the production of biodiesel. Carbohydrates are among the leading products of photosynthesis, and in some species of cyanobacteria, their content can reach up to 50% of the dry weight [106]. These compounds are present in the cell wall (structural support) in addition to being stored as an energy source for the cell [97]. A possible biotechnological application of carbohydrates from cyanobacteria is in the area of biofuels, due to the high content of fermentable sugars and low hemicellulose and lignin contents [15; 107]. In particular, the feasibility of producing bioethanol from the cyanobacterial biomass depends on the content and composition of the carbohydrates in the cell, both varying and depending on factors such as cultivation conditions and species type. Therefore, the production of carbohydrates by cyanobacteria has become the focus of much research [15; 72; 73; 108] due to their potential application as a substrate for biofuels [109]. Some cultivation conditions favor the accumulation of carbohydrates in cyanobacterial cells, including the limitation of nitrogen in the medium where it is cultivated [72]. In Table 6, where the data referring to the accumulation of total carbohydrates can be found, we can observe a large variability according to the species, i.e., from 15% in _Synechococcus_ sp. [69] up to 70% in _Spirulina maxima_[70]. However, the best carbohydrate-accumulating species were also grown in nitrogen-poor media (e.g., wastewater-borne cyanobacteria, _Arthrospin platelets_ NIES-39, and _Spirulina platensis_) [15; 21; 70]. In other words, some species are able to accumulate carbohydrates more than others, but this capacity can be influenced by the medium in which they are grown. Another critical question is the demand for food, which is a worrying factor in the world because of the growing population. According to the United Nations, the world population could reach 8.5 billion in 2030 and increase even more to 9.7 billion in 2050, creating a significant challenge related to food production. In this way, the food sector looks for foods or inputs that can add nutritional value and benefit human and animal health. These products are called functional foods, which provide metabolic and nutritional effects on health and essential physiological functions [80; 83; 107; 109]. The search for a healthy diet and lifestyle causes consumers to purchase products that complement their physiological and metabolic needs. As a result, there has been an increase in this food sector, which focuses on consuming carbohydrates, lipids, and proteins. However, food alternatives have been sought as a source of protein, replacing animal sources [80; 83; 107; 110]. Algae and microalgae have emerged as promising alternative sources of macronutrients. However, one of the problems encountered is the high cost of producing biomass, limiting the applications of its use. Due to this problem, research is being carried out on cyanobacteria, mainly due to the ease of their proliferation, generating much biomass. As the results collected in Table 7 show, cyanobacteria are an excellent source of proteins, either as a food supplement or as an input to increase the concentration of this nutrient in food. Among these microorganisms, _Spirulina_ sp. have stood out due to their excellent properties. They can be applied as biostimulants or biofertilizers, animal feed, or to produce human foods enriched in _Spirulina_ sp., which are already commercially available. In addition, they are used in cosmetics, medicines, and functional foods. These applications, mainly as a source of protein, are possible because they are safe, nutritious, and sustainable raw materials. For this reason, there is much research into the literature on cyanobacteria, as seen in the above tables. Data related to _Spirulina_ sp.