Design of an innovative fiber-rich spreadable cheese up-cycling olive stones: structural and sensory characterization

The olive industry generates annually huge quantities of by-products, including olive stones (OS) which are currently used almost exclusively for energy production through combustion. However, OS could be considered a source of dietary fibers, thus opening the possibility to design alternative valorization pathways in a circulareconomy perspective. To explore this potential, OS (81 % fiber) were locally collected, dried, and milled (particle size < 0.5 mm). The resulting OS powder was then incorporated into a model spreadable cheese formulation before curding, at concentrations of 3.5 and 7.0 g/100 g, to meet the "source of fiber" and "high in fiber" nutritional claims, respectively. The addition of OS induced a significant change in the visual appearance, with an overall darkening of the matrix, without affecting its moisture content. Regarding structural properties, OS inclusion at both levels significantly improved the spreadability of cheese, while reducing its elastic properties compared to the control. Confocal microscopy revealed OS fibers affected the microstructure of the typical threedimensional protein network present in the curd, with large insoluble fiber particles embedded in protein aggregates and acting as inactive fillers. Sensory analysis showed that consumer acceptability remained high, although it declined with increasing OS content. These findings demonstrate that incorporating OS powder at 3.5 g/100 g into innovative spreadable cheese is technologically feasible and nutritionally beneficial, offering a new way for the valorization of OS as a healthy functional food ingredient.