Unlocking the potential of second cheese whey: a comprehensive review on valorisation strategies

The second cheese whey (SCW) is the liquid fraction that remains after the production of whey-2 cheeses. SCW appears as a white to yellow/green opalescent liquid with suspended solids and contains up 3 to 6% lactose and variable amounts of proteins, fats, and mineral salts. Due to its organic load, SCW is 4 characterized by levels of BOD (Biochemical Oxygen Demand) and COD (Chemical Oxygen Demand) that are 5 significantly higher than urban wastewater. Therefore, it poses an environmental challenge and represents 6 a significant cost and a problem for cheese production facilities when it comes to disposal. On the flip side, 7 SCW contains valuable nutrients that make it a cost-effective substrate for bio-based productions including 8 lactose extraction, and the production of lactic acid, bioethanol, eco-friendly bioplastics, biofuels, 9 beverages, bioactive peptides, and microbial starters. A search in Scopus database indicates that despite 10 the numerous potential applications, interest in SCW exploitation is surprisingly limited and, accordingly, 11 sustainable management of SCW disposal remains an unresolved issue. In this review, which marks the first 12 exclusive focus on SCW, with the aim of contributing to increase the interest of both the scientific 13 community and the stakeholders in the exploitation of this by-product, the processes aimed at SCW 14 valorisation will be described, with particular attention to its use in the production of beverages, food and 15 feed, single cell proteins and as a source of biodegradable bioplastics, organic acids and renewable energy. 16 Moreover, to provide valuable insights into its applications and innovations, an overview on patents 17 regarding the exploitation of SCW will be presented.