Optimized Extraction and Antibacterial Activity of Polyphenols from Sour Pomegranate Peel

Pomegranate peel, a rich source of polyphenols, is largely underutilized. To address the challenges of high polarity, poor solubility, and instability of these bioactive compounds, a green ultrasound-enzyme combined extraction system was developed for sour pomegranate (Punica granatum L.) peels from Xinjiang, China. Process parameters were optimized via single-factor tests, Plackett–Burman design, and Box–Behnken response surface methodology. The optimal conditions (cellulase:pectinase = 7:3, enzyme concentration 2.5%, enzymatic hydrolysis at 40 °C for 60 min, followed by ultrasound at 50 °C for 27 min with a solid–liquid ratio of 1:20) yielded a total polyphenol content of 216.2 mg/g, which closely matched the predicted value (0.76% deviation). This combined approach significantly outperformed individual methods in polyphenol yield and antioxidant activity. HPLC identified punicalagin, ellagic acid, gallic acid, catechin, and chlorogenic acid as major phenolics. The extract exhibited antibacterial activity against the two tested bacterial strains, with a minimum inhibitory concentration of 12.5 mg/mL against both E. coli and S. aureus. This efficient, eco-friendly process offers a promising strategy for valorizing pomegranate peel waste.