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Article

The Valorization of Coffee By-Products and Waste Through the Use of Green Extraction Techniques: A Bibliometric Analysis

by
Beatriz Navajas-Porras
1,†,
María Castillo-Correa
2,†,
María D. Navarro-Hortal
3,
Cristina Montalbán-Hernández
3,
Diego Peña-Guzmán
4,
Daniel Hinojosa-Nogueira
5,*,‡ and
Jose M. Romero-Márquez
6,7,*,‡
1
Department of Endocrinology and Nutrition, University Hospital Doctor Peset, Foundation for the Promotion of Health and Biomedical Research in the Valencian Region (FISABIO), 46017 Valencia, Spain
2
Faculty of Pharmacy, University of Granada, 18011 Granada, Spain
3
Department of Physiology, Institute of Nutrition and Food Technology “José Mataix Verdú”, Biomedical Research Centre, University of Granada, 18016 Armilla, Spain
4
Unidad Docente Multiprofesional de Atención Familiar y Comunitaria, Hospital Universitario Reina Sofia, 14004 Córdoba, Spain
5
Unidad de Gestión Clínica de Endocrinología y Nutrición, Laboratorio del Instituto de Investigación Biomédica de Málaga (IBIMA), Hospital Universitario de Málaga (Virgen de la Victoria), 29590 Málaga, Spain
6
Department of Endocrinology and Nutrition, Virgen de las Nieves University Hospital, 18012 Granada, Spain
7
Foundation for Biosanitary Research of Eastern Andalusia—Alejandro Otero (FIBAO), 18014 Granada, Spain
*
Authors to whom correspondence should be addressed.
†
These authors contributed equally to this work.
‡
These authors also contributed equally to this work.
Appl. Sci. 2025, 15(3), 1505; https://doi.org/10.3390/app15031505
Submission received: 14 January 2025 / Revised: 25 January 2025 / Accepted: 30 January 2025 / Published: 1 February 2025
(This article belongs to the Special Issue Extraction and Applications of Bioactive Compounds for Food Products)
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Abstract

:
Coffee is one of the most widely consumed beverages worldwide. This has motivated the coffee industry to adopt sustainable practices, with an increased emphasis on environmentally friendly extraction methods. The objective of this study was to explore, through a bibliometric analysis, the identification of influential researchers, institutions, emerging topics, and gaps concerning the valorization of coffee by-products and residues using green extraction techniques. A total of 7306 scientific publications on green extraction were identified, 72 specifically addressing coffee or its by-products. The analysis highlights a focus on innovative green technologies, such as natural deep eutectic solvents, ultrasound-assisted or microwave-assisted extraction. These methods enable the efficient and sustainable extraction of bioactive compounds, including polyphenols, chlorogenic acid, caffeine, with potential applications in food, pharmaceutical, and energy industries. Despite this, research on coffee by-products remains limited, partly due to their use in other applications, such as biochar, animal feed, and construction materials, which do not rely heavily on green technologies. Key contributors to the field include countries such as Spain, Italy, Brazil, and China. This study emphasizes the potential of coffee waste to generate high-value products through sustainable methodologies, identifies noteworthy research and key actors in the field, and underscores the necessity for further innovation and collaboration.

1. Introduction

Coffee is a traditional beverage with a global market that has experienced significant growth due to increasing consumer demand [1]. Originating as an energy supplement among Ethiopian tribes, coffee is now consumed worldwide in various forms, ranging from traditional infusions like espresso to modern styles such as cold brew [2]. It is estimated that approximately 500 billion cups of coffee are consumed daily [3]. Around 33% of global coffee consumption occurs in Europe, predominantly in Scandinavia, followed by countries in Asia, Oceania, and the Americas, although tea remains the most consumed beverage in some regions [3,4,5]. This rising demand has led to a doubling of coffee production, with cultivation now occurring in over 70 countries, including Brazil, Vietnam, and Colombia, as well as nations in South America, South Asia, and Central Africa [6,7].
The growing demand for coffee has brought several environmental concerns, primarily related to its production and consumption. In 2015, the United Nations introduced the Sustainable Development Goals (SDGs), which, when applied to the coffee sector, have the potential to drive significant improvements in areas such as wastewater treatment, residue management, and labor conditions [8,9]. Key environmental challenges include the high consumption of water resources, the significant volume of waste generated, and the inefficient use of coffee by-products such as coffee pulp, husks, silver skin, and spent coffee grounds (SCGs) [4]. For instance, coffee grounds are one of the most prevalent forms of organic waste globally, posing serious environmental concerns due to improper disposal practices [10].
Despite these challenges, coffee by-products and waste have considerable economic potential because of their composition, which includes valuable compounds such as fatty acids, polysaccharides, polyphenols, and minerals [4]. These materials can be repurposed across various industries, including pharmaceuticals, cosmetics, food, and energy. This creates a circular economy in which these by-products are revalued and transformed into biofuels, biopolymers, bio-fertilizers, food additives, or construction materials [4,6,10].
The process of extracting these compounds and products can be expensive, low yield, or result in significant environmental contamination [11]. Consequently, the sustainable extraction of these compounds has become a significant area of interest, particularly with regard to the use of organic solvents and the implementation of innovative, eco-friendly technologies [12]. The term “sustainable extraction” is used to describe methods that are designed to minimize the environmental impact. This is obtained using less harmful chemicals, a reduction in energy consumption, and an enhancement of the efficiency of the extraction process. The most commonly employed techniques include the use of natural deep eutectic solvents, in addition to methods such as supercritical fluid extraction, ultrasound- or microwave-assisted extraction, and pressurized liquid extraction [11,12,13].
This study aims to examine publication trends, research focus areas, and collaborative networks related to the valorization of coffee by-products and waste through the application of green extraction techniques, using a bibliometric analysis.

2. Materials and Methods

2.1. Methodology Employed in the Search for Scientific Publications

The present study employs a bibliometric analysis to examine the available scientific literature on the subject of green extractions and coffee-related products. Bibliometric analyses are considered to be a robust methodology for facilitating the identification of influential works, leading researchers, and key institutions, in addition to the identification of emerging topics and research gaps [14]. The search and data acquisition process was conducted by compiling all related research using the Web of Science (WOS) database, which is one of the most widely used sources of bibliographic data on scientific research [15]. Due to the presence of methodological challenges, including the lack of homogeneity, which complicates the integration of metadata from different sources, only one source of information was selected for analysis [16]. In order to identify all existing documents up to the end of August 2024, a bibliographic search was conducted using the following keywords: “green extraction” OR “green solvent” OR “sustainable extraction” AND “coffee”. “All Fields” was employed as a filter to identify the greatest number of documents containing the specified keywords. All documents that aligned with these characteristics were selected, and all available information was collected, including the title, keywords, authors, year of publication, abstract, journals, and other relevant elements. All data were extracted in .txt format due to its versatility for further analysis.

2.2. Data Analysis

The initial filter was applied with the objective of identifying all articles that did not include the keyword “coffee” (n = 7306). Subsequently, it was employed as a keyword for the final analysis (n = 72). The number of publications per year were determined for the period from the identification of the first article found to exhibit these characteristics (2011) until August 2024. The WOS categories with the 10 highest numbers of publications were identified as the most relevant. The aforementioned method was employed for the five journals with the highest number of publications. The 10 countries with the highest number of publications and citations were identified as the most relevant for the purposes of this study. The same methodology was employed for the analysis of authors. About institutions, the 20 most highly cited were selected. In addition, out of a total of 515 keywords, 30 keywords with the highest number of occurrences and a minimum of 4 occurrences were selected. Similarly, the 50 words with the highest frequency of occurrence among the total of 2291 words in the title, source, or abstract, which had a minimum of 10 occurrences, were subjected to a similar analysis.
The analysis of publication years, publishers, WOS categories and open access status was conducted using the online analysis platform provided by WOS. The remaining dataset was subjected to bibliometric analysis using the VOSviewer 1.6.20 software, which is designed for the construction and visualization of bibliometric networks [17]. The data were processed and presented as percentages to facilitate analysis and interpretation.

3. Results

A total of 7306 scientific publications related to green extraction were identified, of which only 72 specifically addressed coffee or its by-products. Among the total publications, 77% were original research articles, 18% were review papers, and the remainder were distributed across other document types. Figure 1 illustrates the distribution of publications by year and by country, organized both by the number of publications and the number of citations. Additionally, the figure highlights significant events such as the implementation of the Sustainable Development Goals (SDGs) and the COVID-19 pandemic.
A comparison of WOS categories reveals that the most represented fields are Food Science and Technology (20.3%), Multidisciplinary Chemistry (12%), Chemical Engineering (7.5%), Sustainable and Green Science and Technology (6.8%), and Analytical Chemistry (5.3%). Additionally, the categories of Agricultural Engineering, Environmental Science, Biotechnology, Applied Microbiology, Biochemistry, Molecular Biology, and Applied Chemistry each account for approximately 4%.
The publications are distributed across 52 different journals, with a significant proportion (26.4%) appearing in five primary journals: Foods, Industrial Crops and Products, Sustainable Chemistry and Pharmacy, Journal of Food Measurement and Characterization, and Molecules. However, the journals with the highest citation counts are Food and Bioproducts Processing (255 citations), Trends in Food Science & Technology (230 citations), TRAC-Trends in Analytical Chemistry (174 citations), Waste Management (174 citations), and Molecules (126 citations). Regarding publishers, Elsevier leads with a contribution of 47.2%, followed by MDPI (15.3%), and Springer Nature (9.7%). The total citation count for all articles is 2068, with an average of 28.7 citations per article.
A collaborative network analysis identified key universities and research institutions contributing to this field. Notable connections were observed among institutions such as the University of Cagliari, the Polytechnic Institute of Lisbon, the Bulgarian Academy of Sciences, and the University of Southern Denmark. A temporal analysis (Figure 2) highlights that some of the earliest institutions to adopt an ecological approach to coffee product valorization include the Teagasc Food Research Center and the Federal University of São Carlos. In contrast, institutions such as the Autonomous University of Aguascalientes, Lorraine University, and the University Kebangsaan Malaysia have emerged as recent contributors to this field. Additionally, the CSIR-Central Food Technological Research Institute and the University of Minho stand out as two of the most significant research institutions in this area.
Based on this information, an exhaustive analysis of the most influential authors was conducted, considering both the number of publications and the number of citations (Table 1). The results indicate an absence of overlap between the authors who publish the most in the area and those who receive the highest number of citations. Furthermore, the analysis reveals the absence of any author who has published a substantial number of papers; in this regard, Murthy, Pushpa S, can be identified as the researcher with the most publications.
A gender analysis of the 40 most cited authors revealed that 63% were male and 37% were female. A co-occurrence and cluster analysis of the keywords was conducted (Figure 3). The orange cluster comprises terms such as “phenolic compounds”, “spent coffee grounds”, “bioactive compounds”, “green extraction”, or “supercritical-fluid extraction”, which are related. The purple cluster comprises terms such “antioxidant activity”, “polyphenols”, “optimization”, “chlorogenic acid”, or “caffeine”.
Figure 4 presents the results of the same analysis, but this time focuses on the most frequent words in the publications, specifically in the title, source, and abstract sections. The co-occurrence analysis classified the most frequently occurring words into three predominant clusters, which correspond to the trends observed in the field. The green cluster contains terms related to the conditions and techniques employed in the extraction process, with notable examples including “temperature”, “ethanol”, or “subcritical water”. The orange cluster is concerned with products and applications, and includes terms such as “coffee”, “product”, or “bioactive compound”. The final cluster, in purple, is concerned with studies on bioactive compounds and their properties and includes terms such as “study”, “coffee ground”, “polyphenol”, or “caffeine”.

4. Discussion

The coffee industry has a considerable environmental impact, affecting various aspects such as deforestation, biodiversity loss, high carbon and water footprints, overproduction driven by unsustainable consumption, and poor waste management [9]. This has heightened the urgency for adopting more sustainable methodologies, a call increasingly recognized by social, industrial, and scientific communities. In this context, the concept of “green chemistry” is gaining prominence as a valuable approach with the potential to significantly transform the industry [18]. This affirmation is supported by the scientific literature, which reveals a notable increase in the number of publications related to these green technologies. This growth may be associated with the implementation of the SDGs or the European Green Challenge Agreements, indicating a significant shift in the field [8,9,19]. In this sense, evidence suggests that green policies and agreements have the capacity to mobilize all relevant actors, including the scientific community, in order to identify solutions. Moreover, Figure 1 highlights data from a de-elicitation process that analyzed the research impact of the ongoing COVID-19 pandemic, aligning with findings from other studies [20].
Despite this progress, research focusing on the use of coffee or its by-products remains limited. This may be due to the fact that coffee by-products are often used for other purposes, such as the production of biochar and biochelates [21], animal nutrition [22], biopolymers [23], or the manufacture of construction materials [24], which do not require the use of these green technologies for the obtaining and valorization of the products.
The analysis of countries that have made the most significant contributions to the research and development of sustainable technologies within the context of the coffee industry reveals several key players. These include Spain, Italy, Brazil, India, Portugal, France, and Indonesia, which are consistent with the countries that are the primary producers or the principal consumers [3,4,6,7]. Most of the countries mentioned also exhibit a notable presence in the field, as evidenced by a considerable number of citations. It is notable that China has made a significant impact in this field, not only in terms of the high number of publications, but also in terms of the high number of citations it has received. This is particularly significant given that China is one of the major consumers of tea, rather than coffee [5]. However, this phenomenon may be attributable to the increasing prominence of the coffee industry in China, which has led to an increase in consumption and, consequently, a rise in waste [25]. This has given rise to concerns regarding the environmental impact of coffee production and consumption. Furthermore, China’s transition towards more efficient and sustainable technologies has also contributed to this research trend [26].
The prevalence of WOS research categories such as Food Science Technology or Multidisciplinary Chemistry underscores the interdisciplinary character of the field, which brings together the research areas of food and chemical and technological sciences. This highlights the importance of adopting an integrated approach to address the challenges associated with the ecological valorization of waste or by-products derived from coffee [27]. On the other hand, an analysis of the distribution and scope of the publications, as well as their academic impact, reveals that a number of articles have been the subject of considerable interest within the research community [23,27,28,29,30]. About the relevance of the publishers, it is noteworthy that the largest academic publishers exert a considerable influence over the dissemination of scientific knowledge in the field under consideration, as evidenced by their notable presence in the analysis.
Figure 2 illustrates the absence of big initiatives involving multiple institutions with the objective of fostering partnerships between institutions with the aim of strengthening the transfer of knowledge. Only collaboration between institutions, such as that observed between the University of Cagliari and the Polytechnic Institute of Lisbon, could be considered as evidence of an active research network in Europe, complemented by significant contributions from Asia and South America. The CSIR Center for Food Technology Research Institute and the University of Minho exert a greater influence within the network, as indicated by their greater weight. Institutions such as the University of Lille and the University Kebangsaan Malaysia are contributing to the expansion of knowledge in this area with more recent research.
With regard to the relevant authors, it can be observed that the proportion of women is lower than that of men in this research. This trend is observed across the research field and is reflected in the “Diversity landscape of the chemical sciences” report [31]. It is also important to note, that the most relevant studies in this field have been conducted by women. It is noteworthy that there was no overlap between the 15 most influential authors in terms of the number of publications and those with the highest number of citations (Table 1).
The network of key terms shown in Figure 3 is divided into two principal clusters, one in orange and the other in purple. The orange cluster focuses on concepts related to sustainable extraction methods and waste valorization. Notable terms within this cluster include “phenolic compounds”, “spent coffee grounds”, “green extraction”, “bioactive compounds”, and “supercritical-fluid extraction”. These terms highlight the emphasis on utilizing waste materials, such as coffee grounds, through innovative and sustainable technologies to extract valuable bioactive compounds. This approach prioritizes the use of green technologies to minimize environmental impact while maximizing extraction efficiency [32]. In contrast, the purple cluster is associated with the chemical and biological properties of the extracted compounds, reflecting a focus on their composition, functionality, and potential applications. The terms “polyphenols”, “antioxidant activity”, “chlorogenic acid”, and “caffeine” are particularly prevalent within this group. This reflects the significant interest in the extraction of antioxidant compounds, particularly polyphenols, which are of particular interest due to their beneficial health properties [33,34]. The interconnection between the two groups elucidates the correlation between extraction techniques and the attributes of the resulting compounds, exemplifying the potential of waste as a valuable resource within a circular economy model. For example, the selection of an environmentally friendly extraction method can markedly impact the quantity and quality of the extracted compounds [35].
Figure 4 provides a visual representation of three distinct nodes, which can be clearly differentiated. The green cluster is focused on the technical and environmental parameters associated with the extraction methods. The use of terms such as “temperature”, “microwave”, and “subcritical water” reflects the crucial role played by the experimental conditions and the technology employed in the extraction process. The orange cluster emphasizes the valorization of products and by-products, particularly in relation to the terms “coffee”, “product”, “bioactive compound”, “extraction method”, and “application”. The final cluster, in purple, focuses on the chemical and bioactive properties of extracted compounds, as well as their relation to extraction methods. The use of terms such as “polyphenol”, “caffeine”, “chlorogenic acid”, and “antioxidant activity” indicates a focus on the characterization and analysis of the functional effects of these compounds. Moreover, the numerous interconnections between the clusters illustrate the interdependence of technical, chemical, and application-related aspects. To illustrate, the extraction conditions (green cluster) influence the quantity and quality of the extracted compounds (purple cluster), which in turn affects their use and product valorization (orange cluster). The co-occurrence of words and keywords analyses demonstrate that the sustainable techniques are predominantly employed for the extraction of antioxidant compounds and bioactive supplements. However, they are also utilized for the production of other products, including biodiesel [36,37,38]. One example of the initial green methods employed is the utilization of sunflower oil for the extraction of caffeine, which has resulted in the development of a more sustainable technique [39]. One of the earliest investigations into the use of a bio-renewable agrochemical solvent (ethyl lactate) for the extraction of caffeine was conducted in 2013 [40].
Table 2 presents a synthesis of the most relevant information extracted from the analyzed publications. It focuses on the specific coffee products utilized, the techniques and solvents employed, and the obtained products.
A variety of factors have been identified as contributors to the waste produced by the coffee industry. The quantity and composition of waste is determined by the specific coffee variety, the growth conditions, and the processing methodologies employed [41]. According to recent estimates, in 2020, global coffee production will exceed 2 billion tons in solid waste [42]. This magnitude represents not only an environmental challenge, but also a reuse opportunity for high-value compounds.
According to the bibliometric analysis, the most widely used coffee product is the SCG, which is one of the most abundant residues and has the greatest potential for resource recovery [43], estimated to constitute about 40–45% of the total mass of coffee after brewing [44]. Consequently, a significant proportion of research efforts are directed towards this particular type of waste, given its extensive industrial applications, particularly in the production of cosmetics or food ingredients [42,45]. In addition, the bibliometric analysis highlighted research into other products such as green beans, husk, and pulp, which have been shown to possess a high abundance of bioactive compounds [46,47,48]. These residues are, as a general rule, utilized by various industries, which have invested significantly in the generation of novel high-value products such as bio-sugars or bio-oils [49]. Due to the characteristics of these residues and their significant potential, the food, pharmaceutical, and cosmetic industries are the primary sectors prioritizing their waste management through reuse and recycling [50].
Another crucial element is the extraction method. The results of the bibliometric analysis show that ultrasound-assisted extraction and microwave-assisted extraction are particularly noteworthy, which may be due to their reduced solvent usage, rapid extraction, and energy efficiency [48,51]. For example, the employment of ultrasound-assisted extraction techniques has been demonstrated to result in a substantial enhancement of the total phenol content and antioxidant activity, with a recorded increase of almost 60% in comparison with conventional extraction methods [52]. Microwave-assisted extraction has been identified as a highly efficient and ecologically sustainable extraction method [53]. This finding may be a motivation for researchers to publish more high-quality studies using this method.
Pressurized liquid extraction, along with high-temperature and high-pressure solvent extraction, also stands out [51,54]. The bibliometric analysis has enabled the observation that sustainable technologies such as cold plasma-assisted extraction (CPAE) have not been described in relation to coffee products. This could be a significant technique for extracting polyphenols [53], from coffee waste.
In terms of the type of solvent employed, the most commonly utilized are water [55], and natural deep eutectic solvents. This is due to their biodegradability and low toxicity [47,56]. These findings are consistent with those obtained through co-occurrence analysis. Furthermore, deep eutectic solvents and absolute or hydrated ethanol, a traditional solvent with favorable extraction efficiency [47,51,57], are also employed. The employment of this eco-friendly methodologies has been demonstrated to reduce operating costs by decreasing solvent and energy consumption, thereby optimizing process efficiency and enhancing profitability [58]. An illustrative example is a study on the extraction of oil with supercritical fluids from used coffee grounds, which demonstrates a preliminary economic assessment with a net process yield of approximately 56 million euros per year [59].
Subsequently, the extraction processes yield a range of by-products. The high occurrence of polyphenols and caffeine is indicative of their importance as bioactive compounds of interest. According to the results, the compounds that were found to be most prevalent were caffeic acid and chlorogenic acid and their derivatives. This finding can be attributed to the strong antioxidant properties exhibited by these compounds [56,57,60]. This highlights its importance and value in its recovery from coffee waste for both the scientific community and industry. Caffeine constitutes another significant compound in the analysis. Caffeine represents a highly valuable commercial product and is one of the most relevant compounds in this field [61,62]. As a result, the industry has experienced uninterrupted growth [63], which may be attributed not only to the increase in coffee consumption, but also to the increased consumer acceptance of related products [64]. A clear example of this is the expansion of the caffeinated beverage industry, which is trying to regulate to reduce caffeine consumption in the population [65]. Other important compounds include the polyphenols, including the flavonoids, the catechin or the quercetin [35,36], which possess antioxidant and biological activity and confer significant health benefits [35,36,57]. These compounds serve as functional ingredients in food and nutraceuticals [35,36,57]. Other examples include biodiesels [38,57,66], or pectin and cellulose, among other substances [57,66]. Indeed, it has been demonstrated that biodiesels derived from used coffee grounds generate lower carbon emissions in comparison with fossil fuels. Consequently, in addition to the fact that these new products can be produced in a more environmentally friendly manner, the products themselves can be made more environmentally friendly [67].
An example of the global potential both in terms of economic savings and sustainability can be seen in some studies that, for example, using aqueous solutions are able to extract phenolic compounds from coffee grounds for sustainable applications in the food and pharmaceutical industry [44]. Considering the aforementioned evidence, it is clear that coffee waste and by-products have the potential to create significant opportunities. However, this will only be achieved if there is an increase in innovation and environmental awareness, which will result finally in the transformation of the industry and thus of waste into wealth [68].

5. Conclusions

This study highlights the key actors making increasing efforts to transform coffee waste into high-value products for diverse industries. The results reveal a fragmented landscape, where some institutions demonstrate long-term interest while others have recently become involved. Despite the rise in research related to green technologies, specific studies on coffee waste remain limited. The leadership role in this field is predominantly held by producing and consuming countries, which underscores the importance of developing new technologies and more efficient, sustainable methods to transform coffee waste. The analysis indicates clear interdisciplinary trends, uniting the fields of food, chemical, and technological sciences. The present study also finds that global initiatives, such as the Sustainable Development Goals and the European Green Deal, have significantly increased interest in optimizing the utilization of by-products and waste from the coffee industry. However, achieving more effective sustainability requires fostering collaboration between institutions. Addressing these gaps will facilitate the transition to a more environmentally friendly and resource-efficient model, wherein coffee waste is transformed into significant benefits for multiple industries. This transition not only serves to reduce the substantial volume of coffee waste but also contributes to the establishment of a more robust and sustainable circular economy.

Author Contributions

Conceptualization, D.H.-N.; methodology, B.N.-P., M.C.-C. and D.H.-N.; software, D.H.-N. and J.M.R.-M.; validation, M.C.-C., M.D.N.-H. and C.M.-H.; formal analysis, M.C.-C., M.D.N.-H. and J.M.R.-M.; visualization, B.N.-P., D.P.-G. and C.M.-H.; data curation, M.C.-C., M.D.N.-H., D.P.-G. and C.M.-H.; writing—original draft preparation, B.N.-P., M.C.-C. and D.H.-N.; writing—review and editing, J.M.R.-M.; supervision, D.H.-N. All authors have read and agreed to the published version of the manuscript.

Funding

Beatriz Navajas-Porras is supported by a postdoctoral Sara Borrell contract (CD23/00029) from ISCIII-Madrid (Spain). Daniel Hinojosa-Nogueira is supported by a postdoctoral Sara Borrell contract (CD23/00111) from ISCIII-Madrid (Spain). Jose M. Romero-Márquez is a researcher funded by the Foundation for Biosanitary Research of Eastern Andalusia—Alejandro Otero (FIBAO).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The original data presented in this study were obtained from the Web of Science, and the methodological approach is described in the manuscript.

Conflicts of Interest

The authors declare no conflicts of interest.

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Applsci 15 01505 g001
Figure 1. Evolution of scientific publications by year and country according to the number of citations and the number of publications.
Figure 1. Evolution of scientific publications by year and country according to the number of citations and the number of publications.
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Figure 2. A temporal analysis of the most relevant institutions according to the number of citations.
Figure 2. A temporal analysis of the most relevant institutions according to the number of citations.
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Figure 3. Keyword co-occurrence analysis.
Figure 3. Keyword co-occurrence analysis.
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Figure 4. Co-occurrence analysis of words appearing in publication titles, sources, and abstracts.
Figure 4. Co-occurrence analysis of words appearing in publication titles, sources, and abstracts.
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Table 1. Distribution of authors according to the total number of citations and total number of publications.
Table 1. Distribution of authors according to the total number of citations and total number of publications.
By Number of DocumentsBy Number of Citations
Murthy, Pushpa S. (n = 5)Bubalo, Marina Cvjetko (n = 247)
Aguilera, Yolanda (n= 3)Jokic, Stela (n = 247)
Benitez, Vanesa (n = 3)Redovnikovic, Ivana Radojcic (n = 247)
Martin-Cabrejas, Maria A. (n = 3)Vidovic, Senka (n = 247)
Maimulyanti, Askal (n = 3)Duan, Yuqing (n = 211)
Prihadi, Anton Restu (n = 3)Ma, Haile (n = 211)
Pimpley, Vaibhavi A. (n = 3)Wen, Chaoting (n = 211)
Romani, Aloia (n = 2)Zhang, Haihui (n = 211)
Tiwari, Brijesh K. (n = 2)Zhang, Jixian (n = 211)
Zhang, Zhihang (n = 2)Karmee, Sanjib Kumar (n = 173)
Canas, Silvia (n = 2)Bueno, Monica (n = 168)
Cebello-Hernanz, Miguel (n = 2)Gallego, Rocio (n = 168)
Gil-Ramirez, Alicia (n = 2)Herrero, Miguel (n = 168)
Berego, Patrizia (n = 2)Cheng, Yan (n = 117)
Bettinato, Margherita (n = 2)Du, Shichao (n = 117)
Table 2. Summary of the principal actors involved in the valorization of coffee by-products and waste products using green extraction techniques, extracted from the co-occurrence analysis of words appearing in titles, sources and abstracts of publications.
Table 2. Summary of the principal actors involved in the valorization of coffee by-products and waste products using green extraction techniques, extracted from the co-occurrence analysis of words appearing in titles, sources and abstracts of publications.
Utilized Coffee ProductsExtraction Methods
❖
Spent coffee grounds
❖
Green coffee beans
❖
Coffee husk
❖
Coffee pulp
❖
Leaves of Coffee
❖
Coffee silverskin
❖
Coffee cherries
  • Ultrasound-assisted extraction
  • Microwave-assisted extraction
  • Pressurized liquid extraction
  • High temperature and pressure solvent extraction
  • Subcritical extraction
  • Lyophilization
  • Soxhlet extraction
  • Supercritical CO₂ extraction
  • Electromembrane extraction
  • Subcritical water extraction
  • Physical and enzymatic processes
  • Chitosan films
Products ObtainedSolvents Used
⮚
Caffeic acid
⮚
Chlorogenic acid and derivatives
⮚
Caffeine
⮚
Polyphenolic compounds
⮚
Flavonoids
⮚
Catechin and quercetin
⮚
Phenolic acids (gallic, caffeic, ferulic)
⮚
Antioxidant compounds (melanoidins)
⮚
Modified polysaccharides
⮚
Soluble dietary fiber
⮚
Pectin and cellulose
⮚
Proteins
⮚
Trigonelline and theophylline
⮚
Diterpene esters (cafestol and kahweol)
⮚
Oils
⮚
Biodiesel
⮚
Butanol (produced by fermentation)
⮚
Edible films
▪
Water
▪
Natural deep eutectic solvents
▪
Deep eutectic solvents
▪
Absolute and hydrated ethanol
▪
Ethyls of acetate, butyrate, and propionate
▪
Ethyl lactate
▪
DBU as solvent and catalyst
▪
Isopropanol
▪
Supercritical CO₂
▪
Ethanol-water and acetone-water
▪
Vegetable oils
▪
Citric acid solution
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Navajas-Porras, B.; Castillo-Correa, M.; Navarro-Hortal, M.D.; Montalbán-Hernández, C.; Peña-Guzmán, D.; Hinojosa-Nogueira, D.; Romero-Márquez, J.M. The Valorization of Coffee By-Products and Waste Through the Use of Green Extraction Techniques: A Bibliometric Analysis. Appl. Sci. 2025, 15, 1505. https://doi.org/10.3390/app15031505

AMA Style

Navajas-Porras B, Castillo-Correa M, Navarro-Hortal MD, Montalbán-Hernández C, Peña-Guzmán D, Hinojosa-Nogueira D, Romero-Márquez JM. The Valorization of Coffee By-Products and Waste Through the Use of Green Extraction Techniques: A Bibliometric Analysis. Applied Sciences. 2025; 15(3):1505. https://doi.org/10.3390/app15031505

Chicago/Turabian Style

Navajas-Porras, Beatriz, María Castillo-Correa, María D. Navarro-Hortal, Cristina Montalbán-Hernández, Diego Peña-Guzmán, Daniel Hinojosa-Nogueira, and Jose M. Romero-Márquez. 2025. "The Valorization of Coffee By-Products and Waste Through the Use of Green Extraction Techniques: A Bibliometric Analysis" Applied Sciences 15, no. 3: 1505. https://doi.org/10.3390/app15031505

APA Style

Navajas-Porras, B., Castillo-Correa, M., Navarro-Hortal, M. D., Montalbán-Hernández, C., Peña-Guzmán, D., Hinojosa-Nogueira, D., & Romero-Márquez, J. M. (2025). The Valorization of Coffee By-Products and Waste Through the Use of Green Extraction Techniques: A Bibliometric Analysis. Applied Sciences, 15(3), 1505. https://doi.org/10.3390/app15031505

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