This study pioneered the application of Poria cocos solid-state fermentation (SSF) to Tartary buckwheat (TB). We aimed to enhance its nutritional value, antioxidant activity, and bioaccessibility through fungal biotransformation. Notably, SSF significantly increased protein (by 15.53%) and polysaccharides (by 158%) in TB, alongside a 4.87% improvement in DPPH radical scavenging capacity. Principal component analysis identified 5-day fermentation (FTB-5) as the optimal process, achieving the highest comprehensive score. Furthermore, SSF modified TB’s aroma profile (e.g., increasing 2(3H)-Furanone, 5-methyl by 352.02%) and optimized its amino acid composition, with essential amino acids rising by 12.90%. Critically, in vitro digestion confirmed a higher release rate of bioactive compounds in FTB-5 compared to raw TB. When applied to Chinese steamed bread, FTB-5 imparted a superior sensory score, with a soft texture and an appealing color. This study establishes Poria cocos SSF as a novel strategy for TB valorization, bridging traditional fungal biotechnology with functional food development.

To improve the comprehensive utilization value of wheat bran, solid-state fermentation (SSF) with Wolfiporia cocos was applied for biological modification. The fermentation conditions were optimized by single-factor tests and response surface methodology, and the optimal parameters were 5.20% inoculation amount, a solid–liquid ratio of 1:2.35, and fermentation at 28 °C for 17 days, yielding a FRAP value of 115.20 μmol/g. Unfermented wheat bran (CG) and fermented wheat bran (FWB) were then compared in proximate composition, phytic acid, total phenolics, flavonoids, and triterpenoids, and in vitro simulated digestion properties. After fermentation, the crude protein content increased by 16.0% and the water-soluble dietary fiber content increased by 102.6%, while the phytic acid content decreased by 18.0%. The extractable contents of total phenolics, flavonoids, and triterpenoids increased by 40.53%, 188.55%, and 28.86%, respectively. In vitro digestion showed that FWB released more nutrients and bioactive compounds in the intestinal phase than CG, and protein digestibility increased from 55.5% to 74.2%. The antioxidant capacity of the digestive fluid was also enhanced. Correlation analysis suggested this enhancement was associated with the release of phenolics and flavonoids; however, this relationship should be considered exploratory and requires further confirmation. In summary, Wolfiporia cocos fermentation modifies the nutritional composition of wheat bran, reduces anti-nutritional factors, and facilitates the release of active substances, supporting the valorization of wheat bran as a functional food ingredient and contributing to a more circular utilization of this low-value milling by-product.