Functional and Structural Properties of Extruded Products Enriched with Mushroom-Fermented Flour

Extrusion technology enables the development of nutrient-dense snacks, but most commercial extrudates rely on nutrient-poor cereal flours. This study evaluates the effect of the incorporation of mushroom-fermented flours (MFF) from Ganoderma sessile (GS) and Pleurotus ostreatus (PO), at increasing substitution levels, on the physicochemical, structural, nutritional, and functional (bioactive) properties of corn-based extrudates, relative to a corn control. Partial substitution (10–20%) significantly reduced expansion index and hardness, and reduced or maintained density, relative to the corn control, without causing structural collapse. At 100% substitution, the two species diverged sharply: GS100 retained an expansion index statistically indistinguishable from the corn control and a density numerically closer to, though still significantly different from, the corn control, while developing a markedly lower final pasting viscosity than the corn-containing formulations; PO100 produced the highest density and lowest expansion index of the entire data set, with an essentially flat pasting profile, despite both flours showing comparable shifts in protein, ash, and carbohydrate content. Incorporation of MFF markedly increased protein, ash, total phenols, triterpenes, and reducing power relative to the corn control, with the largest gains at 100% substitution; free radical-scavenging capacity increased significantly only in the 100% MFF extrudates. These results demonstrate that solid-state fermentation combined with extrusion is an effective strategy for producing nutritionally and functionally enhanced snacks.