Waste cooking oils as a sustainable feedstock for bio-based application: A systematic review

Waste cooking oils (WCOs) are common wastes and promising green, eco-friendly and sustainable feedstocks for bio-based applications. While the primary valorisation strategy revolves around the concept of waste-to energy, new research trends have emerged in the last decade. This systematic review provides a comprehensive analysis of the current state of the art in the conversion of WCOs into bio-based molecules. Based on the PRISMA methodology, 64 papers were selected using different databases and sources, such as: PubMed, ScienceDirect, Scopus and MDPI. The data extraction process focused on studies reporting the biological and chemical conversion of WCOs into value-added bioproducts. Many of the selected publications deal with the development of bioactive molecules, including biosurfactants, with application in pharmaceuticals, food, cosmetics, and bioremediation. Bioconversion processes mainly featured engineered Yarrowia lipolytica and Escherichia coli strains, even if additional microorganisms were also employed. In the same way, different chemical processes have been thoroughly studied. A smaller segment of research is directed to the production of feed supplements and soaps. Regulatory constraints limit further development in feed supplements due to potential contaminants, while soap production needs further stability studies. The present systematic review shows promising outcomes in the valorisation of WCOs through the development of value-added molecules and products. Despite the wide range of applications, these findings identify that the scalability and economic sustainability of the selected processes require further investigation. This study seeks to summarize the current state of the art and identify potential gaps to advance the industrialization of WCOs valorisation.