## 1 Introduction  
There are over 30,000 microalgae species; however, fewer than ten species are commercially produced [1, 2], and only two species are recognized for sale within the European Union with European Food Safety Authority (EFSA) approval. Select microalgae contain protein levels based on a dry matter basis, similar to some plant and animal sources of protein. The reported protein content of _Spirulina platensis_ varies from 65% to 77% of the dry matter, a value greater than the protein content of soy flour (37%), chicken (24%), fish (24%), beef (22%) and skimmed milk (36%) [3]. _Isochrysis_ sp. reportedly contains 30.5% protein on a dry weight basis [4]. Although microalgae were used throughout history as a source of food [5], the industrial production of microalgal protein is still a developing field of research due to technical difficulties regarding cultivation, cost of cultivation and processing and limited knowledge regarding their functional, nutritional and bioactive attributes.  
Several research groups have looked at extracting proteins from microalgae, including _Spirulina_ sp. previously. Ultrasound followed by sugaring out with ionic flotation [6] and ultrasound alone were applied to _Spirulina_ sp. previously to disrupt the cell wall [7]. Previously, [PERSON] et al. determined the proportion of proteins released from the microalgae _Porphyridium cruentus_, _Arthospira platensis_, _Chlorella vulgaris_, _Nannochloropsis oculata_ and _Haematococcus pluvialis_, following both mechanical and chemical treatments with a high-pressure disruptor and 2N NaOH [8]. The proportion of essential and non-essential amino acids in the extracts was higher in the alkaline and high-pressure treated samples compared with the untreated algal biomass [8]. A study by [PERSON] et al. assessed the functional properties of protein extracts generated from the brown alga _Himanthalia elongata_ ([PERSON]) [PERSON] [9]. This study suggested that protein extracted from this alga could be suitable for use in the formulation of a wide variety of food products, including sausages, breads, cakes, soups and salads [9]. What protein extraction method is considered the best method depends on the alga treated and the structure of the algal cell wall. Cost is also a factor that should be considered. The type of alga treated, seasonal variations in the quantities of proteins in the starting materials and method all play a part in determining the yield of protein obtainable from a microalga. In addition, the health properties of _Spirulina_ sp. proteins were looked at previously [10]. Protein extracts from microalgae, including _Dunaliella_ sp., at an industrial scale can produce more protein compared with terrestrial plant harvests (about 100 times greater yield).  
The aim of this work was to generate protein extracts from the algae _Spirulina platensis_ and _Isochryss galbuna T-Iso_ using an aqueous sonication method, followed by precipitation with ammonium sulphate and dialysis procedure, as described previously by [PERSON] et al. [11]. The functional and bioactive attributes of the extracted proteins were determined and compared to protein sources including whey protein isolate and flaxseed protein, which are used widely in the food industry as techno-functional ingredients.