Sustainability Impact for Extraction (SIX Score): from Concepts and Principles to Impact-based Metric for Green Extraction Assessment

Abstract

The shift towards a circular and sustainable economy has positioned the biorefinery sector as a key player in the valorisation of industrial by-products, particularly through the extraction of bioactive compounds from agri-food residues. Since its introduction in 2012, the concept of Green Extraction (GE) has established a set of principles aimed at process intensification, reducing energy consumption, minimising of solvent use, and mitigating environmental and safety impacts. Despite the widespread adoption of green chemistry and green engineering approaches, a significant gap remains in the availability of quantitative, accessible, and standardized tools for assessing the sustainability of extraction processes. While life cycle assessment offers a comprehensive evaluation framework, its complexity, cost, and data requirements often limit its routine application, especially during early-stage process development. To address this, the article proposes the SIX Score, a simplified sustainability metric that uses the widely recognized six GE principles as formal reference: 1. raw material renewability, 2. solvent hazardousness, 3. energy efficiency, 4. process robustness, 5. waste production, and 6. extract quality. This framework aims to standardize sustainability evaluations, enabling informed decision-making and facilitating iterative improvements in extraction protocols. The tool, embedded in open-access software (SIX Score Hub), is designed to support the continuous optimization of extraction procedures, fostering scientifically grounded advancements in green technologies and sustainable practices. The manuscript will delve into the application of the chosen criteria of the SIX Score in different extractions scenarios considering different technologies and approaches to highlight its applicability, criticisms and main advantages over traditional green metrics systems. By offering a pragmatic and scientifically grounded evaluation system, the proposed framework aims to provide a solid foundation for the scientific community to further refine, expand, and advance the concept of sustainable extraction.