Plant Waste in the Production of New Materials in Brazil: A Scientometric Analysis from 1991 − 2021

Several plant residues can be generated during the stages of industrial processing, such as fruit peel, seeds and bagasse, and these can give rise to high-value products. The management and use of this waste is of global interest. The aim of this study was to evaluate the spatio-temporal evolution of scientific knowledge on the reuse of agroindustrial waste generated in Brazil through a scientometric analysis. To this end, a search was performed in the databases Scopus, Scielo


Introduction
The world population has gradually increased. Producing food properly, sustainably and of a high quality is a challenge for humanity. Technological development has favored increased productivity, which has significantly intensified the need for sustainability in agriculture due to the environmental impacts associated with the use of fertilizers, pesticides, water and others (Lampridi, Sorensen, & Bochtis, 2019).
Because of their high content of vitamins, minerals and fiber, vegetables are key components for a healthy human diet (Nguyen et al., 2020). Thus, the consumption of fruit and vegetables has been stimulated as a form of disease prevention (Silva, Smith-Menezes, & Duarte, 2016). In the industrial production of vegetable products it is common to use, for example, the pulp of fruit and the disposal of the peel and seeds in significant quantities (Cangussu, Fronza, & Cavalcanti, 2020), with a consequent increase in waste generation (Barbosa & Conceição, 2016).
Waste management and sustainable development are challenging topics for developing and industrialized countries (Patel, 2012). In this context, agroindustrial systems and forestry stand out because they demand a significant availability of biomass linked to the activities of these sectors (Santos, Nascimento, & Alves, 2017). The agricultural sector has challenges to face in the management and adequate food security of waste in order to reduce environmental and socioeconomic impacts (Esparza et al., 2020).
In Brazil there has been growing concern about the management of municipal solid waste, both related to its recovery and in order to reduce its environmental impact. However, initiatives in this direction are still insufficient (Prado et al., 2022). According to Silva, Rosas and Oliveira (2018), the prospects for a decrease in solid waste generation in Brazil are not positive. These authors, when analyzing the situation of the country after the creation of Law 12.305/2010 which instituted the National Solid Waste Policy (Brazil, 2010), pointed out that non-generation, reduction, reuse and, consequently, conscious consumption are still developing very slowly.
It is important, therefore, to investigate what researchers in Brazil have done in the field of scientific research on the reuse of agroindustrial waste so far as a way to assess current trends and direct future efforts. In this context, scientometric analysis can be a very useful tool. Review articles have the function of providing information about academic evolution and helping to monitor the development of science. They present the "state of the art" in a specific subject in order to improve the quality of research, guiding future work through evidence (Blümel & Schniedermann, 2020).
The objective of this study was to evaluate the spatio-temporal evolution of scientific knowledge on the reuse of plant waste generated by the agroindustrial sector in Brazil, with emphasis on the types of reuses proposed for plant residues, predominant areas of knowledge and plant species studied (origin, endemism, and phytogeographic domains).

Methods
The methodological basis of this study was based on scientometrics, a segment of the sociology of science that studies the quantitative aspects of scientific activities. Through indicators that detect the growth and trends of the subject addressed, it provides information on the orientation and scientific and technological dynamics of a country, as well as on its participation in science and technology worldwide (Macias-Chapula, 1998;Parra, Coutinho, & Pessano, 2019).

Collection of Scientometric Data
To compose the dataset of this work, the articles/papers were initially accessed in the databases of the Portal de Periódicos da Coordenação de Aperfeiçoamento de Pessoal de Nível Superior-CAPES (http://www.periodicos.capes.gov.br/); Scopus (Elsevier) (https://www.scopus.com); Scientific Electronic Library Online (Scielo) (https://scielo.org/); and Web of Science (www.webofknowledge.com), between May and June 2022. All databases were searched for papers that presented in their title the following combination of terms: "agribusiness* waste*" OR "vegetable* waste*" OR "fruit* waste*" OR "Biomass* Waste*" OR "plant* residue*" OR "Chemical characterization". The asterisk (*) was used to capture variations in the root of words or singular and plural, p. ex. "plant residues".

Temporal Analysis of Publications
The selected time frame was from 1991 to 2021. As the platforms do not have the same standard for the refinement of searches, there was a need to carry out manual verification of all articles in order to exclude the titles that were not related to the reuse of plant waste.
During manual screening, duplicate file deletions and evaluation of titles and abstracts were performed. The application of these filters was carried out by organizing and reading the files in the programs Zotero 6.0.9 and Microsoft Excel. Review articles were excluded in order to consider only articles that investigated physical-chemical characteristics and the applicability of plant residues.
We obtained 14,084 studies, of which 12,072 were scientific papers. Among these, 144 scientific articles were selected for being published in Portuguese or English, produced in Brazil and addressing the theme "reuse of plant residues" (Figure 1).

Bibliometric Indicators
In order to meet the objectives of the scientometric analysis, the data collected in the 144 selected articles were as follows: year of publication; area of knowledge of the research/researchers; type of reuse; plant species cited in the study; and origin, endemism and phytogeographic domains of the species. The scientific names, origins, endemism and phytogeographic domains of the species were determined according to Flora e Funga do Brasil (2022).

Data Analysis
Data analysis was performed with the help of the Program R version 4.0.0 for Windows. Normality was checked by the Shapiro-Wilk test (p = 0.454), showing that the results do not differ from a normal distribution. In order to express the trend of the number of publications over the years, linear regression analysis and determination of (R 2 ) were performed. The images were generated by QGIS 3.26.0 and Microsoft Excel.

Results and Discussion
Although the search covered the period from 1991 to 2021, the first article on this subject was published only in 1994. Between 1994 and 2021 the number of publications increased linearly, indicated by the equation y = 1.3846x + 2000, R² = 0.7525 ( Figure 2). Solid waste generation is considered a consequence of economic growth, which boosts the population's access to new products and consumer goods, such as energy recovery (Mannarino et al., 2016). The transformations arising from globalization that occurred in the 1990s contributed to the increase in information regarding the implications for the environment. Waste management has been incorporated in urban centers, most of which are in member countries of the Organization for Economic Cooperation and Development (OECD) (Demajorovic, 1995). Thus, it is possible that the beginning of scientific production on this subject from the year 1994 is related to the incorporation of the concept of sustainability in 1992 at the United Nations Conference on Environment and Development in Rio de Janeiro. At this event, documents were prepared that stipulated international commitment to actions that associate development and the environment. From that moment, the matter has become official in most governments in the world (Malheiros et al., 2008).
Although the growth in the number of publications in the first two decades of the evaluated period (1994−2014) may be related to the international agreements on the environment, to which Brazil is a signatory, it is important to note that the most significant increase in publications occurred in the later years (2010−2021). It is possible that this is related to the publication of Federal Law nº 12.305/2010, which establishes the National Solid Waste Policy in Brazil. This policy has as its guiding principle the protection of human health and sustainability in government actions in the field of waste management, with goals that seek to eradicate landfills and encourage environmental solutions considered appropriate for the final disposal of municipal solid waste (Brazil, 2010). It is important to note that according to Normative Instruction Ibama nº 13/2012, which establishes the Brazilian Waste List, residues from agriculture, horticulture, aquaculture, forestry, hunting and fishing are considered solid waste, as are residues from the preparation and processing of food products (Ibama, 2012).
In the same period between 2010 and 2019, the Brazilian Association of Public Cleaning Companies and Special Waste (Abrelpe, 2010) observed a considerable increase in the generation of municipal solid waste in Brazil, from 67 million to 79 million tons per year, in all regions of the country. In 2010, ABRELPE reported that 3,152 municipalities sought a selective collection initiative, and this number increased in the following decade to 4,070 municipalities.
Agribusiness is considered responsible for producing much of the organic waste today. The minimization or reuse of agroindustrial waste is an alternative to reduce the impacts caused by the inadequate disposal of these by-products, since they are a source of organic matter such as proteins, enzymes, essential oils and other chemical constituents (Ricardino, Souza, & Silva Neto, 2020). This has stimulated the development of methods and reuse and, consequently, led to an increase in the number of scientific publications in the area.
The concern with the need to produce more food due to the population increase, and the need to preserve natural resources challenge several areas of knowledge, especially the Natural, Exact and Earth Sciences. This was  mentioned in the studies.
Of the 153 plant species described in the papers (Table 1), the most cited were sugarcane (Saccharum officinarum L.)-18 papers; corn (Zea mays L.)-14 papers; rice (Oryza sativa L.)-13 papers; oats (Avena strigosa Schreb.)-11 papers; and (Passiflora spp)-9 papers. Brazil is considered a major sugarcane producer and exporter in global agribusiness, and 68% of Brazilian production is exported, which represents 5.7% of the total revenue of exports made by the country (Satolo et al., 2016). About 11 million tons of bagasse ash and 14 million tons of sugarcane straw ash can be generated annually. These data show that reusing this waste sustainably has become a necessity and has motivated research in recent years (Berenguer et al., 2020).
Bibliographic data demonstrate trends in the development of innovative materials from sugarcane waste with applications in construction , in wastewater treatment (Lebre et al., 2022), and in power generation (Silva et al., 2019), among others. These data are corroborated by Tessmann et al. (2021), who identified, by scientometric analysis, the use of sugarcane residues such as bagasse, molasses, straw, cake and vinasse in the production of bioproducts such as lactic acid and flour.
Corn is another major crop on the world stage, ranking third in world exports, and is the second most significant crop in Brazilian agriculture . Corn processing generates cob and straw, residues that can be used in the production of bioethanol (Gupta & Verma, 2015) and which are considered viable as a complement to sugarcane ethanol (Silva & Castaneda-Ayarza, 2021). In addition, corn silk, often discarded during the corn processing stages, has the potential to become health products (Gasparoti & Paula, 2021).
Rice is one of the most consumed and produced grains in the world and is considered a staple food. In Brazil, rice has economic and social relevance. The need to adapt rice farming systems in order to improve productivity and ensure sustainability has been the subject of recent discussions (García et al., 2021). The by-products of rice crops are generated in significant quantity. Among them are bran, chirera, bark and ashes of burnt bark . The most frequent use of rice residues is as a fertilizer additive and in plants in the production of thermal and electrical energy (Abaide et al., 2019). Applications of residues were also found in the coproduction of furfural, furfuryl alcohol and formic acid , fertilizer ( Oat is considered an important winter crop in Brazil. The area of cultivation of oats grew around 8% from 2019 to 2020, an increase of about 429.7 thousand hectares, and consequently its production has risen (Azevedo et al., 2022). Oats have different uses, such as in the production of grains for human and animal consumption, production of cosmetics and inputs for the chemical industry, green fertilization, pasture formation or preparation of hay and silage, among others (Mori, Fontaneli, & Santos, 2012). This justifies the search for methods that reuse oat residues, produced in the stages of raw material processing, to obtain fertilizer (Dias et al., 2003;Paredes Filho, Silva, & Florentino, 2020) and for the conservation (Panachuki et al., 2015) and improvement of soil quality (Franchini, Gonzalez-Vila, & Rodriguez, 2002).
Fruit and vegetables are among the most important waste generators in the food processing industry, supermarkets and homes, and waste may exceed 25% of the initial product (Sánchez et al., 2021). This fact is attributed to the regular growth in the use of fruits and vegetables in diets due to the population's search for natural and healthy foods .
In Brazil, passion fruit is a widely consumed fruit. It is estimated that about 60% of the cultivation is intended for fresh consumption, while the rest of the production is used in juices and concentrates in processing. The increase in consumption of this fruit may be related to its nutritional characteristics, such as high levels of vitamins, carotenoids and phenolic compounds. Research has been carried out with the objective of evaluating the chemical composition and the physical-chemical characteristics of. the agroindustrial residues of passion fruit, due to the increase in the availability of these materials . In addition, the residues have also been studied for use as flour (Mendes et al., 2019) in the production of methane (Edwiges et al., 2018), animal feed (Pereira et al., 2020) and biosorbent (Pavan et al., 2008).
Several fruits whose residues were studied in the studies collected here, although less cited, are important in the Brazilian and global scenario. Sustainable reuse can contribute to the bioeconomy and to the fulfillment of the 2030 Agenda for sustainable development, launched by the United Nations (UN) (United Nations, 2017). Bioeconomy is understood as the use of innovative and biotechnological processes for the conversion of biomass into bioproducts (food, biofuels, biochemists, forage, etc.), either as raw material or final product. In this type of economy the production bases, such as materials, chemical compounds and energy, are derived from renewable biological resources (Bueno & Torres, 2022). This new approach to the economy is consistent with the need to rise to value-added raw materials for other sectors given their varied characteristics and applicability. The fermentation of fruit residues can be used in the production of biofuels (Tahir & Amin, 2013). A focus of many countries today is the modernization of biogas for the large-scale production of renewable energy systems, which encourages the valorization of biofuel in the energy system, both economically and environmentally (Angelidakia et al., 2018).
For biogas production, husks, bagasse and fruit seeds are used as biomass in renewable methods such as anaerobic digestion. It is used as a direct energy source in boilers and biogas turbines (Sousa & Rizzatto, 2022).  used residues of açaí, cocoa, coconut, cupuaçu and Brazil nut to evaluate the combustion properties and create renewable energy alternatives for the industry of the Amazon region of Brazil. Similarly, residues of species such as tomato, squash, carrot, and potato were used for the treatment of plant solid waste and the development of scientific knowledge on the kinetics of hydrolysis in anaerobic codigestion systems (Leite et al., 2021).
Plant residues were used long before the Christian age as green fertilization was applied to agricultural systems. Nowadays, they are reemerging as alternatives to conventional forms of agricultural production. They present benefits such as improving the physical-chemical and biological properties of the soil and fertility, providing nutrients for following crops, erosion control and plant protection (Abranches et al., 2021). Biochar can also be produced by different materials containing carbon such as wood, coal and coconut shell, with numerous applications in different areas, but mainly in the environmental area, as one of the adsorbents in water and effluent treatment (Bhatnagar et al., 2013). Studies have shown the use of plant residues in this, such as Ceiba speciosa (A.St.-Hil.), Ravenna, in the adsorption of synthetic phenolic effluent (Franco et al., 2021), sugarcane bagasse, coconut shell and babassu coconut endocarp in the removal of 2,4-D herbicide from water , and Passiflora edulis residue in methylene blue biosorption (Pavan et al., 2008).
In addition, plant waste has been used in construction based on tests making mortar with waste from Pinus caribaea (Stancato, Burke, & Beraldo, 2005) as a mineral additive to partially replace cement from the biomass residue of sugarcane (Anjos et al., 2013) and complementary cementation material resulting from the calcination of elephant grass biomass (Martínez Ramírez et al., 2019). The quality of the concrete is related to the quality of the aggregates used, and the concrete is based on the dosed and homogeneous mixture between aggregates, cement and water (Silva et al., 2022). The use of agroindustrial plant residues in the production of cement and construction derivatives reduces the extraction of mineral resources, which has direct impact on the preservation of natural resources (Pacheco-Torgal & Jalali, 2011).
Different applications of plant residues were little mentioned by the works in the searches. Among them, articles were found that aimed to evaluate residues for the production of compounds of interest to the pharmaceutical industry and polymer production (Branco et al., 2010), chitosan films for food packaging (Mesquita et al., 2020) and cellulose nanocrystals from rice husk (Hafemann et al., 2020). In addition, vegetable waste can be raw materials with the potential to provide solutions in the future for science's demand for biomedical materials (Pelegrini et al., 2019).
The development of products originating from plant waste can reduce the negative socioeconomic and environmental impacts caused by food waste (Esparza et al., 2020). The strategies to valorize residues of vegetable origin are still relatively scarce due to the small amount of knowledge, but the development of biotechnologies can help in this valorization, improving the yield, quality and economic viability (Ganesh, Sridhar, & Vishali, 2022). In this way, research is needed that proposes new applications for plant waste, in order to expand the range of options for the producer market.

Conclusions
Waste management means adopting a set of appropriate actions at all stages of the manufacturing process of a product, from the collection of raw material to the final product. The reuse of agroindustrial plant waste follows the precepts of sustainable development, and seeks to minimize waste production, aiming at the preservation of public health and the quality of the environment. The residues most investigated for reuse were (Saccharum officinarum), corn (Zea mays), rice (Oryza sativa), oat (Avena strigosa Schreb.) and passion fruit (Passiflora edulis, Passiflora alata). Regarding the distribution of species in different Brazilian phytogeographic domains, it was found that the Atlantic Forest, the Cerrado and the Amazon are the most investigated. Publications with residues of species occurring in the Atlantic Forest and Cerrado, two highly threatened Brazilian biomes, may reveal a concern with the conservation and preservation of these biomes.
A significant number of studies investigated the use of plant waste from large crops, due to their commercial importance combined with the great environmental impact that such crops potentially generate. A small number of studies investigated residues of native plant species. These findings open the prospect that research for the use of plant residues from the most threatened biomes, even if generated on a smaller scale from local species in cooperatives and communities, could contribute to the strengthening of the entire production chain. This strengthening, in turn, could be reflected in the greater engagement of communities in actions for the conservation of species, whose residues are confirmed to be useful. Therefore, this is a gap in knowledge in a field where scientific investigations are still insufficient.
The authors evaluated agroindustrial plant waste more frequently, with the objective of generating potential products for food, fertilizer, biofuel, activated carbon, and construction, but 12 papers did not contain the specified application and 33 other applications were less cited. Among the less cited applications, it is worth mentioning those that focused on health (human and animal) and cosmetics, demonstrating that there is another gap in knowledge to be explored here, since plant residues can be sources of pharmacologically active chemical compounds.

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