Characterization and comparative analysis of saponins in various spinach (Spinacia oleracea L.) cultivars according to growing seasons

Spinach is valued for its nutritional benefits, containing essential vitamins, minerals, and functional compounds that support health, particularly through anti-inflammatory and immunomodulatory properties. However, the specific metabolites responsible for these effects remain unidentified. This study quantified total saponin content in 15 spinach cultivars harvested in different seasons, expressed on a dry matter basis (mg/g D.M.), using gravimetric, spectrometric, and HPLC-CAD methods. Five new oleanane-type saponins, spinaciasaponin A, B, D, and E (1, 2, and 4–6), as well as the known compound celosin I (3), were isolated and quantitatively analyzed. The highest total saponin content was found in the spring, particularly in Luckyyou (3.2821 mg/g D.M.) and Shinwoldong (3.2214 mg/g D.M.) cultivars. Spinaciasaponin B (2) was most abundant in Luckyyou (1.1431 mg/g D.M.), while spinaciasaponin E (6) peaked in Shinwoldong (1.3668 mg/g D.M.). This study provides insights into saponin profiling and variation across spinach cultivars and seasons.