*2.3. Data Analysis*

The information of publications was manually extracted. For example, journal impact factors (IFs) were retrieved from Journal Citation Reports (JRC) in 2020. In addition, the number of total citations and the h-index value were obtained from the Scopus database (https://www.scopus.com/search/form.uri?display=basic#basic; collected on 15 July 2021). On the other hand, software such as VOSviewer was utilized to perform bibliometric analyses. VOSviewer was employed to visualize the similarities among different subjects (countries and keywords) [14]. In addition, the visualization map was generated using VOSviewer to display the relationship between subjects in a research field. The research network and keyword co-occurrence network were constructed and visualized with VOSviewer. In the case of the keyword co-occurrence network, the most commonly utilized keywords related to the searched words (fucoxanthin) were screened. The minimum number of occurrences for the keyword co-occurrence network was determined as 15. Manual inspection was performed to eliminate the unrelated keywords. Moreover, the data were analyzed using the bibliometric R-package incorporated in the open-source RStudio software (www.rstudio.com; version 4.0.5, assessed on 15 July 2021) [15].

## **3. Publication Output**

A total of 2080 fucoxanthin research articles were published from 1928 to June 2021 (Figure 1). According to the Scopus database, the first fucoxanthin research article was published in 1928. A small number of publications per year were observed (<10 units except 1976) until 1986. The amount of publication has doubled (around 20 units) per year since 1994. After that, the annual publications have elevated steadily and generated an immediate increase in the cumulative total publications. A remarkable increase in the number of publications was detected starting in 2017. In 2017, the number of publications exceeded 100 for the first time. The last decade's publication on fucoxanthin corresponded to 64.90% (1350 publications) of the total publications since 1928. In addition, the previous years (2017 to June 2021) recorded 35.96% of the total publications on fucoxanthin. These findings indicated that a strong interest in fucoxanthin research occurred recently.

**Figure 1.** The annual and cumulative numbers of fucoxanthin publications from 1928 to June 2021.

The major publications on fucoxanthin were articles (82.55%) (Figure 2). Reviews were the second-largest amount of publications, which constituted 11.25% of the total publications. This is followed by book chapters (2.55%) and conference papers (2.31%). Other documents such as books, conference reviews, data papers, editorials, errata, letters, notes, and short surveys accounted for less than 2% of the total publications.

**Figure 2.** Distribution of publication types for fucoxanthin.

#### **4. Global Production of Fucoxanthin Publications**

Fucoxanthin studies have been conducted over the continentals in the world. The top ten countries have contributed to more than 70 publications from 1928 to June 2021 (Table 1), indicating these countries are the key players in studying fucoxanthin. From the time perspective, the United States predominates in producing fucoxanthin articles among the other countries from 1928 to 2000. Although more articles (*n* = 115) by the United States from 2001 to June 2021 were observed compared to the previous period, the United States could only be classified as a second or third place among the other countries in the last two periods. All these top ten countries demonstrated noticeably increased research performance on fucoxanthin from 1928 to June 2021. The most apparent upsurge of fucoxanthin publications was seen in 2011–June 2021 for the top ten countries except for Canada. For example, China showed the most remarkable productivity (almost 24-fold) on fucoxanthin articles; the number of articles escalated from nine (2001–2005) to 219 (2011–June 2021). Overall, Asian countries focused on fucoxanthin publications more than the other countries, as four Asian countries (Japan, China, South Korea, and India) occupied the top ten countries (1928–June 2021). The major three countries that produced the most fucoxanthin publications were Japan, the United States, and China. Japan leads the first ranking in the publications on fucoxanthin with 379 articles, suggesting that Japan plays a significant role in advancing fucoxanthin research.



TP: Total publications; 2021 \*: up to June 2021.

The top ten institutions contributed at least 33 fucoxanthin publications, respectively (Table 2). These top institutions were leaded by Hokkaido University, Japan (110 articles), CNRS Centre National de la Recherche Scientifique, France (61 articles), and Goethe-Universität Frankfurt am Main, Germany (49 articles). Among these ten institutions, five were European and five were Asian. Institutions from Japan occupied three of the top ten institutions: Hokkaido, Kyoto, and Kobe University. The contribution of these three major Japanese institutions resulted in Japan predominating in fucoxanthin research. Fewer fucoxanthin publications were produced from these top ten institutions in 1928–1990 except for Norges teknisk-naturvitenskapelige universitet, Norway. Most of the top ten institutions increased their publications at least one-fold from the 2001–2010 period to the 2011–June 2021 period. The most remarkable elevation of fucoxanthin publications was produced by the Chinese Academy of Sciences, China (around 18.5-fold).

**Table 2.** Top ten productive institutions in producing fucoxanthin publications from 1928 to June 2021.


TP: Total publications; 2021 \*: up to June 2021.

A distribution by communities of 31 countries with at least 20 articles on fucoxanthin was observed (Figure 3). These countries were distributed over four clusters. The first cluster comprised of eight European countries, along with Chile, Iran, Turkey, and New Zealand. The second cluster consisted of Mexico, Australia, Brazil, and four European countries. The third cluster was made of the United States and seven Asian countries, while Canada and three European countries constituted the last cluster. Based on Figure 3, the United Kingdom established a research collaboration with the highest number of countries (26 countries). The United States was the second country that formed the most partnerships with other countries (25 countries). Germany had the third highest number of country collaborations (23 countries). For the strength of research collaboration, the United States formed the most substantial collaboration network with other countries (total link strength: 214). This is followed by Germany (126), the United Kingdom (125), France (118), and Japan (103).

The top ten productive authors produced at least 18 publications (Table 3). Eight of the top ten productive authors were affiliated with Japanese institutions. No publication was generated from these top ten authors in the first period (1928–1970). The number of the publication produced by Liaaen-Jensen, Synnove (Germany) outweighed the other authors from the second period (1971–1980) to the fourth period (1991–2000). The last two periods were dominated by Miyashita, Kazuo (Japan) in terms of publications. Miyashita Kazuo was the most productive and impactful author on fucoxanthin research with 88 publications and a Scopus *h*-index of 50. The *h*-index was utilized to evaluate a researcher's contribution. The *h*-index not only indicates productivity, it also demonstrates the influence of a group's or scholar's published work [16]. The author recently studied the effect of fucoxanthin/fucoxanthinol on cancer, particularly pancreatic and colon cancer [17,18].

Masashi Hosokawa produced 68 publications and became the second most productive author on fucoxanthin research (Scopus *h*-index: 44). The author worked together with Kazuo Miyashita in examining the effect of fucoxanthin on dexamethasone-induced muscle atrophy and fat mass in mice [19]. The third most productive author was Claudia Buchel (41 publications, Scopus *h*-index: 34), who has investigated the structure and energy transfer of FCP complexes lately [20,21]. Synnove Liaaen-Jensen was among the leading researchers from Norway. The author demonstrated the iodine-catalyzed R/S isomerization of the allenic carotenoids fucoxanthin via the attack of I·on C7 [22]. In addition, the author also studied the diphenyl diselenide-mediated photoisomerization of allenic carotenoids fucoxanthin in benzene solution to optimize synthetic yields of (6S)-allenes [23]. A team led by Ryo Nagao studied the structure and function of a diatom photosystem I-light-harvesting supercomplex [24] and adaptation of light-harvesting and energy-transfer processes of diatoms [25,26].

**Figure 3.** Visualization map of countries communities in fucoxathin research (minimum occurrence: 20).

Multidisciplinary collaboration networks among researchers are crucial in developing, evolving, and enriching the nature of fucoxanthin utilization research. The high productivity of these top ten authors could be attributed to the formation of effective research teams via co-authorship networks. The homophyllous network is a collaboration among researchers of the same gender, academic department, and research interest. This network is vital in establishing and sustaining the research capabilities of the members of the organization. On the other hand, heterophyllous collaboration allowed the cooperation among researchers of different gender, affiliations, and research interests. This cooperation could provide new insights or solutions to complex problems and create transformative research [27].


**Table 3.** Top ten prolific authors in producing fucoxanthin research from 1928 to June 2021.

TP: Total publications; 2021 \*: up to June 2021.

#### **5. Subject Category, Sources and Citations**

At least 2.0% of total publications were assigned to each of the top ten subject categories for fucoxanthin research (Table 4). The global fucoxanthin publication landscape covered 27 subject categories. A total of 27.0% publications was classified under the agricultural and biological sciences category. This category's highest percentage of publications signifies the solid scientific interests in the fundamental knowledge of agricultural utilization [28], synthesis, and accumulation [29,30] of fucoxanthin. The rapid development of biochemistry [24,31] and molecular techniques such as genetic transformation [32,33], sequencing [34], and transcription [35] led to the dominance of biochemistry, genetics, and molecular biology category (18.1% publications). The high number of publications in the pharmacology, toxicology, and pharmaceutics (8.3% publications) category could be due to the increase of health-consciousness and the benefits of fucoxanthin [36,37]. However, a low percentage of articles in the economic and social science categories (data not shown) implies that fucoxanthin research is still in its infancy. Thus, it is crucial to focus on the economic viability and social acceptance of fucoxanthin in the future.

A total of 689 scientific journals published fucoxanthin articles from 1928 to June 2021. The top ten journals on fucoxanthin research belonged to seven different publishers (Table 5). Springer occupied three of the top ten journals. The rest of the journals were owned by Multidisciplinary Digital Publishing Institute (MDPI), Wiley Periodical LLC, Elsevier B.V., Inter-Research Science, American Chemical Society, and Oxford University Press. According to the InCites Journal Citation Reports, the top ten journals showed at least an impact factor of 2.400. The journal with the highest impact factor belonged to the Journal of Agricultural and Food Chemistry (5.279), while the Journal of Plankton Research was the lowest impact factor journal (2.455) among the top ten journals.


**Table 4.** Top ten prolific subject categories of fucoxanthin research from 1928 to June 2021.

TP: Total publications.



MDPI: Multidisciplinary Digital Publishing Institute; IF: Impact factor; TP: Total publications.

> Articles from these ten top journals constituted 22.20% of the total fucoxanthin publications (Table 5). The most productive journal was *Marine Drugs*, with 123 articles covering 5.91% of the total publications. This is followed by the *Journal of Phycology* (67 articles, 3.22%), *Journal of Applied Phycology* (55 articles, 2.64%), *Photosynthesis Research* (39 articles, 1.88%) and *Biochimica Et Biophysica Acta* (BBA)—*Bioenergetics* (38 articles, 1.83%).

> The top ten articles in Table 6 demonstrated at least 178 citations. The data of highly cited publications are impactful, as these mirror the scientific advancement, offer revolutionary insights, and provide a significant perspective on scientific advancement [38]. Each of these articles was owned by one prestigious journal except *Marine Drugs* and the *Journal of Agricultural and Food Chemistry*. *Marine Drugs* possessed two top fucoxanthin publications with a high total citation: Peng et al. (2011) and Xia et al. (2013), while two highly cited fucoxanthin research articles were published in *Journal of Agricultural and Food Chemistry*: Sachindra et al. (2007) and Maeda et al. (2007). Furthermore, the top ten most cited publications were observed in only two of the top ten journals, namely *Marine Drugs* and *Journal of Agricultural and Food Chemistry*. The research article produced by Maeda et al. (2005) in *Biochemical and Biophysical Research Communications* was the publication that received the highest total citation on fucoxanthin research (411). The article demonstrated that fucoxanthin upregulates the expression of mitochondrial uncoupling protein 1 that may attribute to the reduction of white adipose tissue (WAT) weight [39]. The review article summarizes the topical state of understanding and provides an overview of the basic knowledge of fucoxanthin. The second highly cited publication was a review article (356). This review discussed the metabolism, safety, and bioactivities of fucoxanthin [2]. The other research article discovered that fucoxanthin was the major active compound in Japanese edible macroalgae, *Hijikia fusiformis*, which might be responsible for the high antioxidant activity [40]. This article was ranked third in the top ten most-cited publications (348). Most of the top ten cited fucoxanthin articles described and discussed the bioactivities of

fucoxanthin (i.e., antiobesity, antioxidant, antiproliferation, anti-inflammatory) [2,6,39–44]. This could be inferred as the interest of researchers was focused on the bioactivities of fucoxanthin lately.

**Table 6.** Top ten most cited fucoxanthin publications from 1928 to June 2021.

