Synergistic Fermentation of Pu-Erh Tea Residue with a Tailored Bacterium and Enzymes: Unlocking Its Potential as a Sustainable Feed Ingredient

Pu-erh tea residue (Ptr), an insoluble byproduct generated during the industrial production of ready-to-drink Pu-erh beverages, is often discarded as waste despite its substantial nutritional potential. To enhance its feed value, this study developed a microbial–enzymatic synergistic fermentation system. A dominant strain, isolated from decaying tea residue, was identified as Bacillus albus and designated as Bacillus albus C01 (Bacillus.a C01). The Bacillus.a C01 strain was sensitive to all nine antibiotics tested and reduced system pH to 3.9 after 5 days of fermentation. 16S rRNA sequencing revealed that microbial–enzymatic synergistic fermentation enriched Bacillus spp., inhibited Pseudomonas spp., and optimized Ptr quality by upgrading nutrients and degrading tannins. Synergistic fermentation significantly increased the contents of crude protein (+7.50%), soluble protein (+93.32%), acid-soluble protein (+41.87%), reducing sugars (+506.49%), γ-aminobutyric acid (+28.00%), tea polyphenols (+7.47%), acetic acid (+22.87%), and total antioxidant capacity (+23.78%), while decreasing crude fiber (−26.61%), tannins (−90.10%), and suppressing polyphenol oxidase activity (−55.41%). In summary, co-fermentation of Ptr with Bacillus.a C01 and composite enzymes significantly improved its nutritional profile by increasing available proteins and organic acids, and enhancing antioxidant capacity, thereby upgrading this industrial byproduct into a functional feed ingredient. This approach offers a practical strategy to mitigate feed shortages and upcycle solid waste from the beverage industry.