Use of Hazelnut Shells Subjected to Instant Controlled Pressure Drop (DIC) Treatment in Cakes: Physicochemical, Nutritional, Textural Properties, and Pore Structure Using Thresholding Algorithms.

Hazelnut shells are an abundant agro-industrial by-product with potential as a functional food ingredient. This study investigated the use of hazelnut shells subjected to instant controlled pressure drop (DIC) treatment in cake production and evaluated their effects on the physicochemical, nutritional, textural, and structural properties of cakes. The DIC process significantly increased the antioxidant potential of the hazelnut shells, yielding cakes with higher phenolic content and antioxidant capacity than those made with untreated shells. Cakes prepared with DIC-treated hazelnut shells exhibited reduced starch digestibility and a lower glycemic index, indicating potential antidiabetic effects. While incorporating untreated hazelnut shells softened the cake texture, DIC-treated shells preserved texture characteristics closer to the control sample. The cake pore structure-including cell number, total area, average cell size, cell perimeter, and fractal distribution-was analyzed using four thresholding algorithms: Huang, Intermodes, IsoData, and Otsu. The Huang and Otsu algorithms were more effective at detecting small pores, whereas the Intermodes algorithm was more effective at identifying larger pores. In addition, the DIC process improved the cake surface roughness. The findings demonstrate that DIC treatment is an effective approach for enhancing the functional properties of hazelnut shells and their use as value-added ingredients in functional bakery products. PRACTICAL APPLICATIONS: Hazelnut shells, an abundant agro-industrial by-product, can be valorized through DIC treatment and incorporated into bakery formulations. DIC enhances functional and antioxidant properties while maintaining acceptable cake texture and structure. This approach offers a sustainable strategy for converting hazelnut-processing waste into functional ingredients, enabling the development of fiber-rich, antioxidant-enhanced, and potentially low-glycemic bakery products, while supporting clean-label production and waste reduction.