Process–Bioactivity Relationship of Fennel Seed Extracts: Effects of Cryogenic Grinding, Solvent Polarity and Optimisation

This study investigates the influence of normal and cryogenic grinding on the antioxidant properties and bioactive compound profiles of fennel seed (Foeniculum vulgare) powder at varying particle sizes. Methanolic and ethanolic extracts were evaluated for DPPH radical scavenging activity (AAO), total phenolic content (TPC), and total flavonoid content (TFC) using conditions optimised through Response Surface Methodology (RSM) employing an I-optimal quartic design. Statistical analysis confirmed that grinding type and solvent type were the dominant factors influencing all three responses, with their interaction significantly governing flavonoid content recovery. The optimal extraction conditions were identified as cryogenic grinding, methanol as solvent, and a particle size of 200 µm, with an overall desirability of 0.887. Validated experimental values under these conditions were AAO = 87.11%, TPC = 11.31 mg GAE/g, and TFC = 14.18 mg QE/g, with prediction errors within ±5% of model-predicted values confirming the robustness of the developed models. HRLC-MS analysis confirmed that cryogenic grinding preserves a broader and more concentrated phytochemical profile compared to normal grinding. These findings demonstrate that cryogenic grinding combined with methanol extraction at fine particle sizes significantly enhances the yield of antioxidant-rich phytochemicals from fennel seeds, supporting their potential application in functional food and nutraceutical development.