Research frontier refers to a growing trend in research theory and subject content that may be represented using burst keywords
[91][32]. Kleinberg introduced the burst detection approach in 2002. Burst keywords are terms that suddenly increase within a short time
[29][33]. It is possible to reveal the information that does not meet the frequency criteria but has informatics importance in academic advancement using the burst detection approach. It may be more practical and scientific to depict interaction and development trend of research frontiers by identifying hotspots change
[19][34]. CiteSpace (a type of citation visualization software) was used to create the scientific knowledge mapping of burst detection to assess the research hotspots of phycobiliproteins
[92,93][35][36]. Over time, the research emphases and orientations can be more directly represented by analyzing the changes in the most used author keywords in different periods. This study demonstrated that the earlier publications related to phycobiliprotein were its role in photosynthesis and energy transfer to chlorophyll, resulting in a citation burst of “energy transfer” and “photosynthesis” from 1976
[62,74,94][37][13][38]. Phycoerythrin was widely explored due to its fluorescent properties
[59,65][39][40]. Furthermore, the application of phycoerythrin and allophycocyanin in flow cytometry has gained prominence since 1986
[95,96][41][42]. The majority of the phycobiliproteins were identified in cyanobacteria, especially
Arthrospira platensis. The bioactivity properties of phycobiliproteins (specifically antioxidant activity) have piqued the interest of researchers since 2011 and have remained a research frontier until now
[1,5][6][10]. Economically sustainable and environmentally friendly phycobiliprotein extraction methods have also gained popularity and have helped broaden the consumer acceptability of cheaper and safer natural pigments
[71,72,97,98][8][9][43][44].
Phycobiliproteins are mainly found in blue-green algae, yet could also be found in red algae, cyanelles, and cryptomonads
[1][6]. Most researchers used blue-green algae for their phycobiliproteins research, whereas only two red algae genera out of ten were exploited. The recent studies on red algae investigated the structure of phycobilisome in
Griffithsia pacifica and the structural basis of energy transfer in phycobilisome of
Porphyridium purpureum [99,100][45][46]. The
Arhtrospira genus was the most used model organism. The
Arthrospira genus is broadly recognized for its high phycocyanin content
[5][10]. In addition,
Arthrospira maxima has been commercially utilized as a food since 1521
[101][47]. The oldest records of production of
Arthrospira biomass for human consumption are from the Aztecs
[102][48]. Furthermore,
Arthrospira has also been exploited as a protein supplement by the Kanembu tribe of Africa near Lake Chad since 1940
[103][49].
Synechococcus is an unicellular and euryhaline cyanobacterium
[104][50].
Synechococcus is the most plentiful (up to 10
5 mL
−1) and widespread picophytoplankton genus in the open ocean
[105][51]. It is commonly used as a model organism to study cyanobacterial metabolism, particularly photosynthetic research, and has the potential for biotechnological uses
[105,106][51][52]. It is also touted as a phycocyanin and phycoerythrin-rich genus
[107][53]. Furthermore, it has a fast growth rate and an extraordinary resistance to high light irradiation
[104][50]. Hence, these characteristics of
Synechococcus favored most researchers in selecting this cyanobacterium for their study. On the other hand,
Synechocystis and
Nostoc genus are the other blue-green algae frequently employed in phycobiliproteins research due to their high nutritional values, and they are widely commercialized.
Synechocystis has received attention in modeling studies and biotechnological applications due to a variety of characteristics including its fast growth, the potential to fix carbon dioxide into valuable products, and the relative simplicity of genetic modification
[108][54]. Despite
Synechocystis, the
Nostoc genus is employed as a food and feed supplement in Mongolia, China, and South America
[103][49].
Nostoc commune has long been recognized as a worldwide nutritious meal and traditional medicine
[109][55]. A wide variety of notably pharmacological and protective physiological properties of the
Nostoc genus aroused the attention of researchers
[109][55]. On the other hand, the number of algae commonly claimed as toxic genera (
Microcystis, Anabaena, Phormidium, and Nostoc) was lower than the nontoxic algae genera (
Porphyridium, Oscillatoria, Gracilaria, Synechocystis, Arthrospira, and Synechococcus). This indicated that more studies were focused on the benefits of cyanobacteria and their bioactivities.
Microcystis and
Anabaena are the most important toxic cyanobacteria bloom genera in terms of diversity, impact potential, and cascading ecological effects
[110,111][56][57]. Although numerous microalgae species are available in various culture collections worldwide, only a minority have been thoroughly studied
[25][58]. Strains such as
Haematococcus pluvialis (main source of astaxanthin),
Dunaliella salina (the major source of beta-carotene), and
Spirulina platensis (prime source of phycocyanin), are the examples of microalgae that have finally reached commercial-scale success
[9,87,112][59][28][60]. Hundreds of many strains have been described in the literature as sources of phycobiliproteins. However, the lack of strain robustness or low productivity under outdoor environments has been typically cited as the cause of the failure of these strains in achieving commercial-scale production
[25][58].