A Multivariate RSM–PLS Framework and HPLC Polyphenolic Profiling for Characterizing Distinct Extraction Signatures in Pressurized Liquid vs. Conventional Stirring Extraction of Asteraceae Species

The current research investigates the extraction efficiency of an emerging green technology, pressurized liquid extraction (PLE), compared to traditional stirring extraction (STE) in order to recover higher antioxidant capacity from three plant species of the Asteraceae family, namely Solidago virgaurea, Tussilago farfara, and Helichrysum stoechas. The optimal PLE conditions were achieved through a combined response surface methodology (RSM) approach. The resulting optimized PLE parameters (40% ethanol, 160 °C, 25 min, 1700 psi) were experimentally verified and directly contrasted with STE (40% ethanol, 80 °C, 60 min, 500 rpm). Despite having the same solvent polarity, the two methods showed significant variations in mass transfer kinetics and heat intensity. Across all species, PLE significantly boosted the ascorbic acid antioxidant capacity (p < 0.05), thereby showing enhanced recovery of compounds that contribute to the overall antioxidant capacity. STE generated noticeably increased total polyphenolic content and DPPH radical scavenging activity (p < 0.05), indicating that some phenolic subclasses might be susceptible to PLE at higher temperatures. Values for ferric-reducing antioxidant power were largely similar among approaches. Overall, PLE was shown to be highly effective in maximizing the total antioxidant capacity in shorter extraction times, while STE can better preserve specific polyphenolic fractions, as demonstrated through analysis of the optimal extracts by HPLC-DAD. The integration of experimental validation with chemometric modeling supports the reliability and practical applicability of the optimized PLE protocol.