Optimized Extraction and Component Identification of Physalis alkekengi L. Calyx Polyphenols and Antioxidant Dynamics During Thermal Processing

Physalis alkekengi L. has attracted widespread attention and cultivation due to its unique lantern-shaped fruit and various bioactivities. Existing studies have mainly focused on its fruit, while the calyx, despite its significant bioactivity, has long been neglected. In particular, research on the changes in polyphenol content and antioxidant activity during its drying process remains scarce. This study aimed to optimize the extraction process, comprehensively profile the polyphenol composition, and evaluate the effects of the drying temperature on the polyphenol content and antioxidant capacity in the calyx of Physalis alkekengi L. (CPAL). Ultrasound-assisted extraction (40 kHz, 300 W) combined with response surface methodology was used to optimize the extraction conditions. The optimized parameters were determined as a 49% ethanol concentration, a 42 mL/g liquid-to-material ratio, a 64 °C extraction temperature, and a 29 min extraction time. Under these settings, the yield reached 10.44 ± 0.16 mg GAE/g, exceeding that of the conventional heat reflux extraction method. Using high-resolution mass spectrometry, 63 polyphenolic compounds were identified, primarily derivatives of kaempferol, quercetin, and hydroxycinnamic acid; 43 of these compounds were first reported in CPAL. CPAL polyphenols possess potent antioxidant activities, with IC50 values of 68.77, 12.76, and 101.24 μg/mL for DPPH, ABTS, and FRAP, respectively. Furthermore, as the drying temperature increased, the polyphenol content and antioxidant activity of CPAL increased significantly. These findings provide a scientific basis for the development of natural antioxidants and functional foods.