## 4 Conclusions  
The foaming capacity and stability values observed for both microalgal protein extracts, along with their solubility at pH 10-12 and excellent OHC values, suggest that these proteins could be used in the formulation of a wide variety of foods with alkaline pH values and with an oil consistency such as that in green drinks with a pH greater than 9.5 and tomato juices. Based on the FC and FS, the microalgal extracts have good stability independent of the pH value compared with flaxseed. However, the aqueous solubility of the extracts limits applications. The renin-angiotensin-aldosterone system (RAAS) controls hypertension development through the actions of two enzymes: renin (EC 3.4.23.15) and ACE-I (EC 3.4.15.1). In a previous study, the response surface methodology (RSM) was used to generate hydrolyses with ACE-I inhibitory activities from _Isochrysis gulana_ (not _Spirulina_ sp.). The conditions that produced the greatest ACE-I inhibitory activity were a temperature of 55.64 \({}^{\circ}\)C, a substrate concentration of 5.46 g (100 mL)\({}^{-1}\) and a trypsin enzyme/substrate ratio (E/S) of 6.27% [37]. The highest ACE inhibitory activity observed was 47.62% ACE-I inhibition at a concentration of 1 mg/mL [33]. The ACE-I inhibitory values observed in this study (95%) were greater than 47.62% at a concentration of 1 mg/mL compared with Captopril\({}^{\circledR}\), the positive control which was assayed at a concentration of 0.05 mg/mL. The renin inhibitory control was also assayed at the same concentration. In addition, the protein extracts generated were found to inhibit renin [38]. In addition, the observed ACE-I and renin inhibitory activities shown by the protein extracts suggest that they could find applications in functional foods for preventative healthcare. _Spirulina_ is certified as generally recognized as safe (GRAS)--GRN No. 127--by the United States  
Figure 6: ACE-I and renin inhibitory activities of proteins extracted from _Spirulina_ sp. and _Isochrysis gulana T-Iso_, assayed at a concentration of 1 mg/mL compared with the control (Captopril\({}^{\circledR}\)) (n = 3) and 10 uM Z-Arg-Arg-Pro-Phe-His-Sta-Ile-His-Lyss-(Boc)-OMe (renin inhibitor).  
(US) Food and Drug Administration (FDA) and complies with the requirements for use set out by Regulation (EU) 2015/2283 on novel foods [25]. However, the presence of contaminants and anti-nutritional factors as well as allergens should be evaluated as discussed previously. The bioavailability and bioavailability of the ACE-I inhibitory activities should be characterized, especially when these ingredients are incorporated in different food matrices, a driving factor of such important nutritional and health benefits [38]. This data is essential for preventative or adjuvant therapeutic strategies against high blood pressure and associated diseases.  
Conceptualization, S.B. and M.H.; methodology, S.B.; writing--original draft preparation, S.B.; writing--review and editing, M.H.; supervision, M.H.; project administration, M.H.; funding acquisition, M.H. Both authors have read and agreed to the published version of the manuscript.  
Teagasc grant number NFNY-6889-142 funded this research.  
Not applicable.  
This project was carried out as part of the BioAlgae Project (Teagasc funded project no. 2016-073). [PERSON] is in receipt of a PhD Walsh Fellowship (grant no. NFNY 6889-142) funded by Teagasc for the period of 2016-2020. The authors would also like to acknowledge the EUALGAE COST Action-European Network for algal bioproducts ESI408.  
The authors declare no conflict of interest.