What is the impact of research with Morus nigra? – A scientometric study

Mulberry (Morus spp.) is an evergreen tree belonging to the Moraceae family. The genus Morus has numerous described species, including Morus nigra, an important plant in agriculture and traditional cultures. The objective of this study was to conduct a scientometric research on the species M. nigra. Bibliographic data was been obtained from the Web of Science database considering two times periods. These analyzes showed that research involving M. nigra is concentrated in the areas of nutrition, pharmacology and agronomy science. Eastern countries and Brazil are the largest producers of knowledge about M. nigra. The research has shown different interests in recent decades, showing that the scientific knowledge produced about the species is associated with the objective for which the plant was used throughout history. There is a trend in the growth of publications focused on the potential antioxidant of M. nigra products. The articles had a greater impact factor in the past, however, a significant growth trend in research with M. nigra in the last three years, also suggested by the increase in the number of publications in the period. Understanding the publication standards assist in directing future research as well as in understanding the current panorama of research associated with the species.


Introduction
The genus Morus consists of approximately 24 species, a subspecies, with at least 100 varieties being described (Tutin et al., 1996). The taxonomy of this genus is complex, with more than 150 of the described species, but only 10 to 16 are generally accepted. Classification becomes even more difficult due to the frequent hybridization between species and the fact that many of them are fertile. Within the genus Morus, the species Morus nigra L (1753), popularly known as, blackberry, originates in Iran and disperses to different parts of the world (Ercisli & Orhan, 2007). In Brazil, its probable introduction occurred in the colonial period (Almeida, 2002;Kumar& Chauhan, 2008). However, its large-scale cultivation began with Japanese immigration in the 1900s (Padilha et al., 2009).
The development of M. nigra is strongly been determined by climatic conditions. Very high temperatures tend to hinder its growth. The cultivation of blackberry was introduced in 1970 by the Experimental Station of Pelotas, now Embrapa Clima Temperado. Since then, the cultivation areas have been expanding from Rio Grande do Sul to São Paulo and Minas Gerais (Antunes, 2002). In terms of world production, there are 20,035 hectares cultivated with an increase of 45% of the planted area in the last 12 years. In South America the values are approximately 1,597 ha. In Brazil, approximately 250ha with a production of 780 tons, of which about 15% are, exported (Clarck, 2006). M. nigra is widely used in food and also pharmacology, with different proven biological activities (Padilha, 2009).
Scientific interest in M. nigra in Brazil began in 1972 with the genetic improvement program proposed by Embrapa through the planting of seeds produced by more than fifty crossings carried out at the University of Arkansas, producing more than 12,000 seedlings, originating the first cultivars (Bassols & Moore, 1981). As a pioneer in the production of blackberry, the state of Rio Grande do Sul is the largest producer, reaching around 700 tons/year. The state is considered the main Brazilian producer, where the Tupy variety is grown, which corresponds to 70% of the cultivated area (Lorenzi, Bacher & Lacerda, 2006). The cultivation of mulberry consists of a rustic plantation, with easy management and that does not require large extensions of planted area and therefore promising for family farming (Antunes, 2002).
Considering that the spatial distribution of M. nigra in Brazil is historically linked to the development of research, at first linked to agronomic science, in addition to the nutritional and pharmacological potential of the species, the objective of this work was to investigate the reasons that guide research on M. nigra, globally in the last decade, evaluating factors that can show which trends in research with M. nigra from the quantitative analysis model or scientometric study.

Methodology
In order to know the historical scenario and the perspectives in research with M. nigra, a bibliographic survey was carried out, with a scientometric character, where mathematical tools are used to help formulate hypotheses and predict phenomena involving the topic of interest. (Pereira et al., 2018). The bibliographic survey used in the study was carried out on the Web of Science database using the descriptors "Morus nigra NOT Black mulberry" and "Black mulberry NOT Morus nigra" present in the title field. Only productions in the "original article" or "review" format were been used. Two searches were been carried out, without time restriction and another with a filter in the period from 2009 to 2019. The diversity of journals obtained in the search was been evaluated using the Shannon-Wiener ecological index (H ') (Carvalho, Diniz-Filho & Bini, 2005;Carneiro, Nabout & Bini, 2008) commonly used in scientometric studies. To assess the time trend in studies with M. nigra, we chose to analyze the Principal Component Analysis (PCA) based on the grouping of keywords by year of publication (Carneiro et al., 2008;Nabout et al., 2012). The data were been submitted to statistical analysis with the aid of the PAST 4.01 software (Hammer, Harper & Ryan, 2001).

Results and Discussion
The research resulted in 184 publications between original articles and reviews, distributed over four decades of  This interest is probably been linked to the origin of the species as well as cultural aspects. Mulberry is a plant of Iranian origin, but with worldwide distribution. Its cultivation varies according to the traditional use of the region, for example, in Tunisia M. nigra is only for the production of fruits that can be eaten fresh or processed (Aljane & Sdiri, 2016). In some countries like China and India, mulberries have been cultivated since the 16th century, especially to obtain leaves that serve as food for the creation of Bombyx mori (Ercisli & Orhan, 2007). Elsewhere in the world, fruits are been consumed in a variety of ways and leaves are used to make teas and even to feed ruminants in some countries (Ercisli & Orhan, 2007;Kumar & Chauhan, 2008). M. nigra brought to Brazil in the colonial period and has adapted very well to climatic conditions, such as subtropical and tropical climate (mild to hot climate). In Brazil, it seems introduced since the colonial period (Almeida, 2012;Kumar, Chauhan, Bhardwaj, Kumar & Tyagi, 2011). It is a species that has expanded its cultivated areas in recent years, from Rio Grande do Sul (main Brazilian producer) to other states where the climate is favorable. M. nigra stands out on the national scene for its adaptability to the environment, for its productivity, as well as for its high value as a functional food among others. The Brazilian production of M. nigra went from 250ha to 500ha between the years 2005 and 2014. By 2017, 527.8ha had already planted (Antunes et al., 2014). This cultural and economic panorama justifies the interest of these countries in researching different aspects related to the species.
Publications with M. nigra have concentrated, especially in recent years, on three areas of knowledge: food science, medical chemistry and agriculture science (Figure 3 -a). This trend is evident when looking at the magazines with the largest number of publications with the term "Morus nigra" (Figure 3   M. nigra fruits have a sweet or slightly acidic taste, when ripe they have a black color (Morgan, 1982). They are consumed fresh or processed, such as jams, syrups, drinks, dehydrated, and can also been used in the production of natural dyes (Gundogdu et al.,2011). In addition to food use, the species is also been used for therapeutic purposes. In traditional Chinese medicine, M. nigra leaves are used as an antiphlogistic, hepatoprotective, hypotensive, antipyretic, analgesic, diuretic, expectorant, against diabetes symptoms (Chen et al. 1995), as well as in the treatment of anemia and arthritis (Özgen, Serçe & Kaya, 2009). The agronomic value of M. nigra is associated with the production of biomass to feed cattle and B. mori herds (Park et al., 2013;Wu et al., 2013).   The concentration of studies involving the elucidation of the chemical composition of M. nigra is probably associated with popular practices, where different parts of the plant are been used in preparations to M. nigra for various medicinal purposes. Its leaves have widespread use mainly for the treatment of diabetes, cholesterol, cardiovascular problems, obesity and gout (Oliveira et al., 2018). Previous studies have shown that extracts prepared with M. nigra leaves reduce blood glucose and cholesterol levels (Volpato et al., 2011). Its roots and bark may have anti-anemic, anti-inflammatory action when associated with arthritis and rheumatism, in addition to anti-hypertensive (Özgen et al., 2009;Hu et al., 2018). Other research also has been shown anti-aging (Hu et al., 2018;), antibacterial, cytotoxic and antioxidant, antidepressant and neuroprotective, anti-inflammatory and antinocepective (Chen et al., 2016;Cruz-Calsavara et al., 2018Ribeiro et al., 2019Lim & Choi, 2019), neuroprotective effect (Kawvised, Wattanathorn & Thukham-Mee 2017) and nutraceutical (Miljkovick et al., 2015).
The growing interest in researching M. nigra appears mainly associated with the anti-oxidant potential presented by its extracts, concentrating the studies associated with this potential, suggesting that future research is focused on this activity.
High intake of plant products is associated with a reduction in the risk of different chronic diseases associated with oxidative damage. According to Podsedek (2007) this protection is attributed to substances that have antioxidant activity, such as vitamins C and E, carotenoids, phenolic compounds and especially flavonoids; that interrupt the oxidative process by absorbing free radicals. It is believed that supplementing the diet with herbs, containing high concentrations of compounds capable of deactivating free radicals, also has beneficial effects (Capecka, Mareczek & Leja, 2005).
Reactive oxygen species and their probable involvement in human pathophysiology have attracted the interest of several sectors of society involved in public health (Laguerre, Lecomte & Villenueve, 2007). The mechanisms by which these pathologies develop come from oxidative changes in important molecules such as proteins, carbohydrates, nucleic acids, in addition to the substances involved in the modulation of gene expression and inflammatory responses (Kawanish et al., 2002).
The actions of antioxidant molecules abundant in the fruits of M. nigra can act in the protection of the organism against oxidative damage and consequently in the progress of some chronic diseases. act entirely in neutralizing the action of the reactive classes or with their function to indirectly contribute to enzymatic systems (Oliveira et al., 2018) making it an interesting object in the research and development of drugs and nutraceuticals.

Conclusion
Research on M. nigra research has shown that the scientific knowledge produced about the species is associated with the purpose for which the plant has been used throughout history. This fact is proven when it was observed that scientific production in the fields of nutrition and pharmacology has an epicenter in eastern countries where its culinary and medicinal use is more widespread in addition to having a historical and cultural character. In Brazil, research in agricultural science is dominant, standing out, following the trend of expanding the cultivation of mulberry in the country.
The articles had a greater impact factor in the past, however, a significant growth trend in research with M. nigra in the last three years, also suggested by the increase in the number of publications in the period. It was noted that the researchers' interest is concentrated on the antioxidant potential presented by the different blackberry preparations. In this sense, the trend is for research with M. nigra to continue expanding, suggesting that scientific production is associated with research, optimization and development of products associated with the species' antioxidant potential. However, more surveys should be carried out to better understand the state of the art of research with M. nigra and its nutritional and pharmaceutical potential.