Population growth combined with increasingly limited resources of arable land and fresh water has resulted in a need for alternative protein sources. Macroalgae (seaweed) and microalgae are examples of under-exploited “crops”. Algae do not compete with traditional food crops for space and resources. This review details the characteristics of commonly consumed algae, as well as their potential for use as a protein source based on their protein quality, amino acid composition, and digestibility. Protein extraction methods applied to algae to date, including enzymatic hydrolysis, physical processes, and chemical extraction and novel methods such as ultrasound-assisted extraction, pulsed electric field, and microwave-assisted extraction are discussed. Moreover, existing protein enrichment methods used in the dairy industry and the potential of these methods to generate high value ingredients from algae, such as bioactive peptides and functional ingredients are discussed. Applications of algae in human nutrition, animal feed, and aquaculture are examined.

The renin-angiotensin-aldosterone system (RAAS) plays an important role in regulating hypertension by controlling vasoconstriction and intravascular fluid volume. RAAS itself is largely regulated by the actions of renin (EC 3.4.23.15) and the angiotensin-I-converting enzyme (ACE-I; EC 3.4.15.1). The enzyme dipeptidyl peptidase-IV (DPP-IV; EC 3.4.14.5) also plays a role in the development of type-2 diabetes. The inhibition of the renin, ACE-I, and DPP-IV enzymes has therefore become a key therapeutic target for the treatment of hypertension and diabetes. The aim of this study was to assess the bioactivity of different oat (Avena sativa) protein isolates and their ability to inhibit the renin, ACE-I, and DPP-IV enzymes. In silico analysis was carried out to predictthe likelihood of bioactive inhibitory peptides occurring from oat protein hydrolysates following in silico hydrolysis with the proteases papain and ficin. Nine peptides, including FFG, IFFFL, PFL, WWK, WCY, FPIL, CPA, FLLA, and FEPL were subsequently chemically synthesised, and their bioactivities were confirmed using in vitro bioassays. The isolated oat proteins derived from seven different oat varieties were found to inhibit the ACE-I enzyme by between 86.5 ± 10.7% and 96.5 ± 25.8%, renin by between 40.5 ± 21.5% and 70.9 ± 7.6%, and DPP-IV by between 3.7 ± 3.9% and 46.2 ± 28.8%. The activity of the synthesised peptides was also determined.

There is growing consumer demand for food products derived from microalgae, driven largely by the perceived health benefits associated with them. The functional and bioactive potential of proteins isolated from two microalgae—Spirulina sp. and Isochrysis galbanaT-Iso—were determined. The results obtained show the potential of microalgal protein extracts for use in the beverage industry, based on solubility values and other functional characteristics, including water and oil holding capacities, foaming, emulsifying activities and stabilities, water activities, solubility and pH. The solubility of algal proteins was pH-dependent, and they were largely insoluble at pH values between 2 and 11. However, the proteins were increasingly soluble at a pH of 12, and they have potential use in formulating foods with higher viscosities or gels, where they could act as fillers to strengthen networks. Compared with whey and flaxseed proteins, the Spirulina sp. protein extract had a superior oil-holding capacity (OHC). The OHC is important in developing texture in food products such as meats. Overall, better foam stability was observed for both Spirulina sp. and Isochrysis sp. soluble protein extracts, compared with flaxseed protein at pH values from 2 to 10 over a period of 120 min. The foam capacity and stability increase the physical properties of foods. However, the emulsion activity and stability values for soluble algal protein extracts were less than the values observed for flaxseed and whey proteins. Algal proteins would not be suitable for use in creaming and food processing involving flocculation. In addition, algal protein extracts inhibited Angiotensin-converting enzyme−1 (ACE−1) and renin, and they have potential for use in functional food ingredient applications to maintain heart health and also to act as meat substitutes.

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