## 4 Discussion
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 significantcontributions 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.