Effects of Steam Explosion Combined with Ultrafine Grinding on the Physicochemical Properties, Antioxidant Capacity, and Volatile Profiles of Morchella sextelata Stipe Powders

Morchella sextelata stipe is an underutilized by-product with potential for value-added food applications. This study investigated whether steam explosion (SE) pretreatment could enhance the effects of subsequent ultrafine grinding (UG) on the physicochemical properties, antioxidant capacity, and volatile profiles of stipe powders. Conventional grinding, UG, SE, and combined SE-UG treatments were compared using particle-size analysis, SEM, FT-IR, XRD, antioxidant assays, and HS-SPME-GC-MS. SE-UG reduced the median particle size (D50) from 88.88 to 10.46 μm and increased the water solubility index from 31.20% to 36.55%. It also caused extensive microstructural disruption and altered crystallinity without major changes in functional groups. SE-UG showed the highest DPPH and ABTS radical-scavenging activities, whereas SE and SE-UG exhibited similarly high total antioxidant capacity, with no significant difference between the two treatments. Volatile profiling showed treatment-dependent changes, with several furans and pyrazines occurring at higher relative abundances in SE-containing groups. These findings indicate that SE pretreatment facilitates subsequent UG and improves selected physicochemical and antioxidant properties while markedly modifying the volatile profile, supporting the value-added utilization of M. sextelata stipes.