Integrated HPLC-DAD and multivariate analysis for exploratory prioritisation of candidate marker compounds in Lactuca...

Lactuca indica L. is a medicinal plant widely used in traditional Vietnamese medicine. A validated HPLC-DAD method was developed for the simultaneous quantification of four selected phenolic compounds, chlorogenic acid, caffeic acid, luteolin-7-O-glucuronide, and luteolin, in 12 batches collected from northern Vietnam. The method showed good linearity (R² ≥ 0.9999), recoveries of 97.8-102.7%, repeatability of 1.15-1.72% RSD, intermediate precision of 1.73-3.37% RSD, and LOD/LOQ values of 0.02-0.84/0.07-2.79 µg mL^-1. DPPH radical scavenging activity showed substantial between-batch variation, with IC₅₀, extract values ranging from 30.40 to 97.91 µg mL^-1. Principal component analysis revealed notable variation in phenolic compound profiles, while partial least squares regression explored the relationship between phenolic composition and antioxidant activity. An integrated HPLC-DAD/PLSR analysis identified chlorogenic acid and luteolin-7-O-glucuronide as the variables most closely associated with DPPH radical-scavenging activity (VIP > 1), providing a data-driven basis for their prioritisation as candidate markers for DPPH-oriented quality evaluation of L. indica.