Processing effects on metabolites and volatiles in turnip (Brassica rapa L.) products: a targeted metabolomics study

Turnips are rich in phenolics, saponins, and glucosinolates, but how different processing forms reshape their nutritional composition, aroma characteristics, and metabolite profiles remains unclear. This study aimed to systematically compare raw turnip (LL) with four processed products, including oral liquid (KF), powder (FM), syrup (TJ), and tablets (PJ), and to identify processing-associated compositional and aroma differences. HS-SPME-GC-MS, sensory evaluation, antioxidant assays, and UPLC-Q Exactive/MS-based targeted metabolomics were integrated. FM showed the highest total sugar content (413.4 mg/g DW), whereas KF had the highest soluble sugar content (211.98 mg/g DW) and antioxidant capacity. PJ exhibited the highest total phenolic (3.62 mg GAE/g DW) and flavonoid contents (2.58 mg RE/g DW), retained relatively high saponin content (1.82 mg/g DW), and showed the greatest diversity of detectable polyphenolic metabolites. FM was enriched in dihydromyrcenol (513.31 μg/L), KF was characterized by phytol (77.15 μg/L), whereas TJ contained geosmin (161.29 μg/L), and PJ in nonanal (691.17 μg/L) and phenethyl acetate (208.27 μg/L). These findings provide an integrated basis for selecting processing strategies according to the desired compositional and aroma attributes of turnip-derived products.