## 1 Introduction  
Microalgae and cyanobacteria are a very interesting group of photosynthetic microorganisms that have strong potential for use in the food industry as a source of valuable biomolecules (proteins, lipids, pigments, etc.). They have attracted increased interest as cell factories, and as an alternative pathway to traditional practices that employ heterotrophs. As they are photosynthetic microorganisms, they might provide simpler cultivation facilities and easier processes (no sterilization required, low contamination potential, etc.) for the production of biomass and the subsequent biomolecules [1, 2, 3]. More recently, microalgae have attracted attention for the production of carbohydrates (polysaccharides) and as a potentially renewable source for various applications in the food and chemical industry [4, 5, 6, 7, 8]. Microalgae and cyanobacteria synthesize carbohydrates through photosynthesis and carbon fixation processes. Carbohydrates have diverse structural (cell walls, etc.) and metabolic (energy storage, etc.) roles. The most common carbohydrate types found in microalgae and cyanobacteria are cellulose as structural carbohydrates (in microalgae), and starch (in microalgae) or glycogen (in cyanobacteria) as energy storage molecules [8]. Among the different carbohydrate types, \(\beta\)-glucans are of particular interest due to their bioactive functions, including immunomodulation, antitumor, antioxidant and antibacterial activities, serum cholesterol and glucose reduction, obesity prevention, etc. [9]. Consequently, \(\beta\)-glucans are considered as a very interesting source for the preparation of functional foods [10; 11]. So far, the main sources of \(\beta\)-glucans that have been investigated are cereals, fungi (yeasts, mushrooms, etc.) and bacteria [12]. Similar studies on \(\beta\)-glucans from microalgae and cyanobacteria are scarce [13; 14; 15]. _Arthrospira_ (commonly known as Spirulina) is an edible cyanobacterium that is produced worldwide as a food supplement owing to its high nutritional value. It is one of the most commercially produced species and is regarded as a very good source of proteins, with a content of more than 60% DW, pigments (phycocyanin and chlorophyll), vitamins, antioxidants, etc. Generally, _Arthrospira_ displays strong potential as an important ingredient in the development of novel functional foods that fulfil consumer demand for nutritional and health-beneficial food [16; 17]. Regarding the polysaccharides from _Arthrospira_, several studies have demonstrated their biological activity [18; 19; 20] and their potential for use in the food industry [4; 21]. However, there are no studies known so far that deal with \(\beta\)-glucans produced by _A. platensis_. An important aspect in regard to the biotechnological application of _A. platensis_ is that its carbohydrate content can be significantly increased (from 10-20% up to 50-70%) by triggering the accumulation of carbohydrates through the manipulation of given cultivation parameters, such as temperature, salinity, nutrient availability and light intensity [5; 6; 22]. Nutrient starvation/limitation (such as nitrogen or phosphorus) of _A. platensis_ has been widely studied and proven to be a very effective technique for carbohydrate accumulation [6; 23; 24; 25] that could also be easily applied in large-scale cultivation systems [22; 26]. Nevertheless, there are only a few studies that have focused on the characterization of the carbohydrates produced by nutrient-starved/limited _A. platensis_ with regard to nitrogen starvation/limitation [22; 27; 28], while there is lack of work characterizing the carbohydrates accumulated by the phosphorus starvation/limitation process. The aim of the present study was to optimize the carbohydrate production of _A. platensis_ through phosphorus limitation and to characterize the produced biomass in terms of the content of glucan types, dietary fiber, and the monosaccharide profile.