Impact of thyme oil enrichment and drying on microstructure and physicochemical quality of pumpkin snacks: A fractal analysis approach

Abstract

The global market for dehydrated vegetable-based snacks has expanded significantly, driven by consumer preferences toward natural healthy products. This study explores convective dehydration (50–70 °C) not only as a preservation technique but also as a platform for developing functionally enriched pumpkin snacks (Cucurbita moschata) containing free and microencapsulated thyme essential oil. The snacks microstructure was characterized through an integrated imaging approach, including Scanning Electron and Confocal Laser Scanning Microscopy together with and Fractal analysis. Thermodynamic stability was evaluated analyzing water sorption isotherms and glass transition temperature. Results identified 70 °C as the optimal drying temperature, yielding the highest total polyphenol content (196.33 ± 16.16 mg GAE/100 g db) and antioxidant capacity (15.35 ± 0.94 mg TE/100 g db) while simultaneously optimizing sensory acceptability and process time (170 min.). Samples containing microencapsulated oil exhibited higher fractal dimensions (ranging from 1.810 to 1.840) and lower lacunarity values (decreasing from 0.4785 to 0.3012) at magnifications of 1000x and 5000x, respectively. These samples presented a reduced W-parameter from the GDW water sorption model showing a fundamental modification in water-matrix interactions. Microencapsulated enriched samples exhibited superior thermal stability, reflected by higher Tg values (e.g. 29.33 °C at 20% H2O). Antioxidant capacity of these samples highlighted their protective role on bioactive compounds (DPPH: 64.57 mg TE/100 g db) compared to free oil impregnated samples. These findings underscore the synergy between microscopy together with fractal image analysis as a robust framework for the design of innovative microencapsulated-oil plant-based snacks with tailored functional and structural properties.