Development of Leather-like Materials from Enzymatically Treated Green Kiwi Peel and Valorization of By-Products for Microbial Bioprocesses

The management and possible valorization of agro-food waste is a major issue in the pursuit of a zero-waste economy. Green kiwi peel (GKP), the primary byproduct of kiwi fruit consumption, offers an attractive source of raw material for the development of biobased polymer films due to its availability and composition, which includes cellulose, hemicellulose, and pectin. In this study, we aimed to entirely valorize GKP by combining material functionalization and biomanufacturing approaches. Starting from mechanically ground GKP, either citric acid or two commercial enzyme preparations were employed to treat the biomass and obtain biobased films. Remarkably, the enzymatic treatment selectively consumes some of the component biopolymers, modifying their ratio. As a result, the mechanical properties of the GKP-derived films can be tuned depending on treatment conditions, offering the possibility of matching different requirements. We also show that the byproduct of biopolymer treatments, which is an acidic liquid fraction rich in glucose and fructose, can be used to formulate growth media for industrially relevant yeast cell factories, namely Saccharomyces cerevisiae, Yarrowia lipolytica, and Rhodotorula toruloides. Hence, the study presents a way to the full exploitation and valorization of the starting material. Overall, we propose an integrated approach with the aim of fully valorizing GKP, showing a versatile methodology that could be applied to other agro-food wastes to make them suitable for similar valorization pathways.