Abstract
Silybum marianum (L.) Gaertn, viz. milk thistle, has been the focus of research efforts in the past few years, albeit almost exclusively restricted to the medicinal properties of its fruits (achenes). Given that other milk thistle plant organs and tissues have been scarcely investigated for the presence of bioactive compounds, in this study, we present a phytochemical analysis of the extracts of S. marianum capitula during the flowering phenological stage (stage 67). Gas chromatography–mass spectroscopy results evidenced the presence of high contents of coniferyl alcohol (47.4%), and secondarily of ferulic acid ester, opening a new valorization strategy of this plant based on the former high-added-value component. Moreover, the application of the hydro-methanolic extracts as an antifungal agent has been also explored. Specifically, their activity against three fungal species responsible for the so-called Botryosphaeria dieback of grapevine (Neofusicoccum parvum, Dothiorella viticola and Diplodia seriata) has been assayed both in vitro and in vivo. From the mycelial growth inhibition assays, the best results (EC90 values of 303, 366, and 355 μg·mL−1 for N. parvum, D. viticola, and D. seriata, respectively) were not obtained for the hydroalcoholic extract alone, but after its conjugation with stevioside, which resulted in a strong synergistic behavior. Greenhouse experiments confirmed the efficacy of the conjugated complexes, pointing to the potential of the combination of milk thistle extracts with stevioside as a promising plant protection product in organic Viticulture.
Highlights
IntroductionCarduus marianus L.), commonly known as milk thistle, St. Mary’s Thistle, or wild artichoke, is an herbaceous plant of the Asteraceae family
As expected from the phenological stage in which the plants were collected and taking into consideration that the entire capitula were used for the extraction, the panel of extracted components was different from those present in the commercially available milk thistle seed extract: instead of silybin (A and B) and isosilybin (A and B), coniferyl alcohol and other eugenol analogues were identified; and instead of vanillin, the quantitative presence of its precursor was evidenced
Current approaches to obtain coniferyl alcohol are either inefficient, harmful (Penicillium simplicissimum (Oudemans) Thom vanillyl alcohol oxidase (PsVAO) can be used to produce it, but it intrinsically produces harmful byproduct H2 O2 ), or expensive [43,44]. These limitations can be overcome with the ultrasonic-assisted hydro-methanolic extraction of the capitula, reported in this paper, which may allow for the obtainment of the phenylpropanoid coniferyl alcohol with a yield of 50–80%
Summary
Carduus marianus L.), commonly known as milk thistle, St. Mary’s Thistle, or wild artichoke, is an herbaceous plant of the Asteraceae family. Native to the Mediterranean area, it is nowadays grown in many countries as a medicinal plant, due to the variety of biological activities—mostly linked to the hepatoprotective properties and anti-carcinogenic capacity—associated with the main pharmacological active ingredient extracted from its achenes (fruits): silymarin [1,2]. The standardized extract obtained from the dried fruits of S. marianum contains. 70–80% of silymarin and 20–30% of polymeric and oxidized polyphenolic compounds [3]. Silymarin is a flavonolignan complex of polyphenolic molecules, which includes diasterereoisomers silybin A and silybin B (whose mixture in a 1:1 ratio is named silibinin), 4.0/)
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