###### Abstract  
The increased demand for protein sources combined with a decrease in the available land and water resources have led to a growing interest in macroalgae as alternative protein sources. This review focuses on strategies for macroalgae protein extraction, enrichment and characterization. To date, the protein extraction methods applied to algae include enzymatic hydrolysis, physical processes and chemical extraction. Novel methods, such as pulsed electric field, microwave-assisted, pressurized liquid and supercritical fluid extractions, and the application of smart solvents are discussed. An overview of the use of membranes and other processes to generate high-value protein concentrates from algae extracts is also presented, as well as some examples of the methods used for their characterization. The potential bioactivities from macroalgae-derived proteins and peptides, including novel glycoproteins and lectins, are briefly reviewed. macroalgae; seaweed; protein extraction; bioactivity +
Footnote †: journal: Medical  
result of environmental and biological stimuli as individual populations exhibit phenotypic plasticity and adaptation to their environment. Because they often experience stressful conditions and highly fluctuating environments, most algae possess mechanisms to enable acclimation to stressors (e.g., UV radiation, temperature and salinity) and are able to defend themselves against biological pressures (e.g., competitors, grazers and/or parasites). This wide range of tolerance combined with their specific cellular structure predisposes them to growth and development under both laboratory and industrial conditions [2]. Macroalgae are multicellular algae with thalli-like structures that can adhere to solid underwater surfaces or float freely in water. They inhabit ecosystems with varied salinities, from freshwater rivers, ponds and lakes to brackish estuaries and the open sea and seashores. Compared to other algal groups, such as microalgae, they occupy available space slower, but grow faster and are less vulnerable to grazing and water turbulence [3]. Macroalgae are classified as green, red and brown algae, according to the thallus color derived from natural pigments. Green algae belong to the _Chlorophyta_ phylum and have the same ratio of chlorophyll \(a\) to \(b\) as terrestrial plants. There are about 4500 species of green algae [4]. Red algae are included in a single class, _Rhodophyceae_, which consists of two subclasses: _Florideophylcidae_ and _Bangiophyceae_. The red color is attributed to the pigments chlorophyll \(a\), phycoerythrin and phyoccupanin. There are about 4000-6000 red algae species in over 600 genera [5]. Brown algae are classified as _Phaeophyceae_ and their principal photosynthetic pigments are chlorophyll \(a\) and \(c\), \(\beta\)-carotene and other xanthophylls. Circa 1500-2000 species of brown algae have been identified so far [6]. Marine macroalgae (seaweeds) are vertically distributed from the upper zone (sea surface) to the lower sublittoral zone [7]. In fact, although many species thrive in littoral zones, some red algae inhabit deeper sea areas (over 25 m below the surface) whereas others are found under rocks, where direct sunlight availability is limited [8]. This is because red algae use a different part of the light spectrum from that used by other algae and thus are able to grow in places where the other algae cannot grow. Macroalgae are photoautotrophic and therefore use photosynthesis to produce and store organic carbon by using CO\({}_{2}\) or HCO\({}_{3}^{-}\)[9]. The photosynthetic rates of macroalgae highly depend on the species although green and red algae usually have higher rates than their brown counterparts (by 1 or 2 orders of magnitude) [3]. When comparing macroalgae and terrestrial plants, significant differences in the chemical composition can be pinpointed in addition to the physiological and morphological ones.