# Current Status and Economic Prospects of Alternative Protein Sources for the Food Industry
## 2 Alternative Protein Sources
### Algae  
Algae-based protein sources are associated with seaweeds and microalgae and have gained increased attention in the food industry over the last decade ([PERSON] et al., 2020) [36]. Both seaweeds and microalgae are photosynthetic, oxygen-producing organisms, but seaweeds are macroscopic, multicellular, marine species of algae, while microalgae are unicellular, microscopic forms. Algae species used for protein production are known to contain protein concentrations similar to animal-based sources such as meat, egg and milk ([PERSON] et al., 2014) [26], while delivering 4-30 times higher protein productivity, when compared to plant-based protein sources such as soybeans and pulses, and requiring far less resources ([PERSON] et al., 2022) [37]. In fact, marine seaweeds, for example, do not require fresh water or arable land to grow ([PERSON] et al., 2019; [PERSON] et al., 2022) [38; 39]. Among seaweeds, brown, green and red algae are commonly used for human consumption, especially in East Asia. According to the Food and Agriculture Organization of the United Nations (FAO, 2023) [40], the Republic of Korea is the largest consumer market of algae, followed by China and Japan. High-protein seaweed species such as _Undaria pinnatifida_ (brown algae, 24 g protein/100 g dry weight), _Ulva lactuca_ (green algae, 32.7 g/100 g DW) and _Porplura_ spp. (red algae, 50 g/100 g DW) are considered promising candidates for alternative protein production. Among microalgae, _Arthospira platensis_, also known as _Spirulina_, and _Chlorella vulgaris_ are the most commonly cultivated species, with multiple applications as functional foods and generally regarded as safe (GRAS) both by the Food and Drug Administration (FDA) and the European Food Safety Authority (EFSA) ([PERSON] et al., 2022; [PERSON] et al., 2022; [PERSON] et al., 2021) [37; 41; 42]. In addition to the relatively high protein content, algae-based protein is considered a favorable source of essential amino acids, comparable to eggs and soybeans ([PERSON] et al., 2023; [PERSON] et al., 2022) [39; 43]. Given that the amino acid profile is highly dependent on species, growth parameters and phase, algae-based protein generally meets the essential amino acids standards. On the other hand, it has been associated with lower digestibility, when compared to traditional sources of plant-based and animal-based proteins ([PERSON] et al., 2014; [PERSON] & [PERSON], 2012) [26; 28]. [PERSON] and [PERSON] (2022) [44] evaluated the in vitro digestibility of different species of seaweed and reported PDCAAS levels ranging from 8%, for _Fucus vesicusus_ (brown algae), to 69%, for _Palmaria palmata_ (red algae). Among microalgae, the two most common species, _Spirulina_ and _Chlorella_ spp., are reported to present PDCAAS of around 77-84% ([PERSON] & [PERSON], 2022; [PERSON] et al., 2021) [42; 44]. However, the digestibility of algae protein is still poorly described in literature, since the shift of algae utilization as a source of proteins is relatively recent. The technological attributes of algae-based proteins are comparable to traditional plant-based proteins, which contributes to their introduction in traditional food model systems ([PERSON] et al., 2020; [PERSON] et al., 2022) [45; 46]. Solubility, foaming, emulsification and gelation capacities, for example, have been found to be pH-dependent, which is also the case for most proteins from plant and animal sources, with a lower performance under acidic conditions closer to the isoelectric point, and favored under alkaline conditions, where the proximity to the pKa of amine groups favors solubility and decreases hydrophobic repulsion ([PERSON] & [PERSON], 2017; [PERSON] et al., 2019; [PERSON] & [PERSON], 2021) [47; 48; 49].