High-Level Expression of a Novel Tannase from Penicillium oxalicum in Aspergillus niger for Enzymatic Production of Punicalin from Pomegranate Peel

Pomegranate peel, a polyphenol-rich byproduct, is a valuable resource for punicalin production. A novel tannase ( Po TanA) from Penicillium oxalicum was expressed in Aspergillus niger FBL-B, producing a maximum activity of 450.6 U mL –1 through high cell density fermentation. Po TanA exhibited optimal activity at pH 6.0 and 45 °C, with remarkable stability under acidic conditions (pH 2.5–6.5) and temperatures up to 45 °C. It demonstrated broad substrate specificity, showing highest specific activity toward methyl gallate (224.1 U mg –1 ). The tannase was further used to directly hydrolyze the pomegranate peel for punicalin production. When applied to pomegranate peel hydrolysis under the optimized conditions (pH 6.0, 40 °C, and 20 U mL –1 ), Po TanA produced punicalin at a yield of 20.2% with a conversion rate of 90.5%, the highest reported to date. These results highlight Po TanA as an efficient biocatalyst for sustainable valorization of pomegranate waste into high-value punicalin.