Exploitation of <i>Pleurotus ostreatus</i> Processing Stems for the Production of Powders Using Different Drying Methods

ABSTRACT The effects of hot air and freeze‐drying methods on the drying behavior, physicochemical properties, functional characteristics, total phenolic content, antioxidant activity, and microstructural properties of mushroom stem powders were investigated. The freeze‐drying process was performed at −25°C and 0.8 mbar, while the air‐drying process was studied at 40°C, 55°C, and 70°C. Air‐drying kinetics were better described by Page's model. Higher air‐drying temperatures caused a decrease in bulk density from 0.837 g/cm 3 at 40°C to 0.807–0.814 g/cm 3 at 55°C–70°C. The freeze‐dried powder had a much lower bulk density (0.470 g/cm 3 ; tapped 0.572 g/cm 3 ). Dried stem powders showed fair flowability characteristics according to the Carr Index (10–17.67) and Hausner Ratio (1.11–1.22), both of which depended on the drying method. Freeze‐drying provided better retention of functionality and color, being lighter colored and having less browning in comparison with air‐dried samples. The total amount of phenolics was at a maximum at 40°C air drying (80.18 mg GAE/g d.s.), with the freeze‐dried powder maintaining maximum phenolic functionality. SEM images showed that the freeze‐dried powder had a porous, flake‐like structure in comparison with the collapsed and more compact structure of the hot‐air dried. In summary, freeze‐drying produced higher‐quality Pleurotus ostreatus stem powder suitable for various food applications, including soups, sauces, bakery products, and meat alternatives.