An Exploratory Study on the Influence of Frying on Chemical Constituent Transformation and Antioxidant Activity in Ziziphi Spinosae Semen: A Multimodal Analytical Strategy Based on UPLC–Q–TOF–MS and GC–IMS

Ziziphi Spinosae semen (ZSS) is renowned for its rich nutritional composition and is traditionally consumed in China, Japan, and Korea, where it is widely incorporated into both medicinal diets and daily cuisine. To address the lack of systematic research comparing raw and fried ZSS, this study aimed to elucidate the compositional and functional changes induced by the frying process. This study systematically compared the chemical profiles and antioxidant activities of ZSS and fried ZSS using ultra-performance liquid chromatography–quadrupole–time-of-flight mass spectrometry (UPLC–Q–TOF–MS) and gas chromatography–ion mobility spectrometry (GC–IMS). A total of 92 non-volatile compounds and 43 volatile organic compounds (VOCs) were identified. Frying significantly promoted the formation of polar compounds such as flavonoids and saponins and increased the content of aldehydes and alcohols, thereby generating aromas characteristic of Maillard reactions and lipid oxidation. Principal component analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS-DA) clearly distinguished the two groups in terms of their chemical composition and flavor characteristics. In addition, 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assays demonstrated that the antioxidant capacity of fried ZSS was significantly higher than that of the raw sample (p < 0.05). These results indicate that the frying process reshapes the chemical properties and bioactivity of ZSS via multiple pathways, including glycoside hydrolysis, lipid oxidation, and Maillard reactions. Overall, this study establishes a scientific foundation for the development of functional foods derived from ZSS.