Toward efficient recovery of the alkaloid plantagonine from Verbascum sinuatum flowers: Optimization of microwave-assisted and pressurized liquid extraction methods

The increasing scientific interest in Verbascum sinuatum L. flowers (VSFs) is due to their potential applications across multiple sectors, including the pharmaceutical, cosmeceutical, and food industries, particularly in the development of functional foods and nutraceuticals. The phytochemical composition of VSFs is predominantly characterized by phenolic compounds, iridoid glycosides, and alkaloids such as plantagonine. This bioactive alkaloid identified in VSFs has been reported to have anticancer, antioxidant, and antimicrobial activities. In the literature, no studies have addressed the optimization of plantagonine extraction from VSFs. Thus, this study aimed to maximize the extraction of plantagonine from VSFs through microwave-assisted extraction (MAE) and pressurized liquid extraction (PLE). For MAE, 2g of dried VSF powder was placed in a closed vessel and dissolved in 40 mL of a solvent at various concentrations (S) and temperatures (T) and for various periods of time (t). Regarding PLE, the procedure involved placing 1g of dried VSFs in a 66 mL extraction cell containing diatomaceous earth under 10 bar pressure and applying various S, T and t conditions. Efficient recovery, meaning the maximization of the yield using the lowest possible inputs, was determined using the Response Surface Methodology (RSM) with three independent variables (t/X₁, T/X₂, and the proportion of ethanol in the hydroethanolic solution, S/X₃), employing a five-level circumscribed central composite design (CCCD) comprising 28 experimental runs. The plantagonine content in the VSF extracts obtained under the operational conditions for each point of the experimental design was evaluated through HPLC-ESI-QqQ-MS/MS. The results revealed that under the optimal extraction conditions, the yield obtained using PLE (2312.86 ± 39.69 µg/g extract; 25 min, 200°C, 59% ethanol) was 1.7-fold higher than that obtained using MAE (1356.20±32.10 µg/g extract; 25 min, 180°C, 55% ethanol). Therefore, this study proposes, for the first time, the optimal extraction conditions for maximizing the recovery of plantagonine from VSFs using two green extraction techniques, demonstrates the superiority of PLE, and provides a quantitative framework for further industrial extraction and application in the food, cosmeceutical, and pharmaceutical industries.