3.2. Chromatographic AnalysisLC-MS/MS analysis revealed that the studied F. vulgaris extracts contain several classes of phenolic compounds, mainly different types of flavonoids, but also phenolic acids and aldehydes. A total of 24 individual phenolic compounds were identified, and their quantification is detailed in Table 2. As can be seen, the presence in the extracts of quercetin, astragalin, gallic acid and kaempferol stands out.The highest number of polyphenols was detected in the dried flower extract, which, in general, also showed the highest concentrations of the compounds, as can be seen in Figure 3. This stacked column chart has been constructed with the concentration values in µg mL−1 and shows the relative contribution (%) of the polyphenol concentration of each sample subgroup (indicated by colors) for individual compounds.Figure 4 summarises the results for the determination of polyphenols in the different extracts. The most significant compounds in the alcoholate were quercetin, gallic acid, astragalin, and kaempferol, all at concentrations above 10 ppm (see Table 2). The 3- and 4-hydroxybenzoic acids and 4-hydroxybenzaldehyde were only detected in this sample. The composition of the extracts obtained from the fresh and frozen flower samples is quite similar. Of note is the high concentration of quercetin-3-glucoside in the dry sample extract, a compound that was identified exclusively in this extract.

As indicated above, the polyphenolic content of the hydrolate was negligible. Their use in cosmetics is not related to their polyphenol content, but to their content of volatile compounds and thus to their flavouring properties.

The results of the LC-MS/MS determination consistently support the values obtained for the spectrophotometric indices (TPC and AA). In general, the concentration of polyphenols in the alcoholate was the lowest, which explains its lower TPC and AA values. Similarly, the higher number of compounds identified and their higher concentrations in the dry extract of Filipendula are consistent with the higher TPC and AA values of this extract. The contribution of some specific polyphenols in higher concentrations in the fresh flower extract, such as catechin or astragalin, could explain its higher antioxidant activity. In this regard, it is important to note that structure–activity relationships play a very important role in determining whether compounds will exhibit an antioxidant effect [28,29]. Therefore, the AA index values can vary significantly between different classes of compounds, even between compounds of the same type [30].Five of the compounds identified in Filipendula extracts in this work, namely gallic and ellagic phenolic acids, catechin, quercetin, and astragalin, have also been found in the methanolic extracts of Filipendula underground organ air-dried samples at different stages of development [14]. The presence of gallic acid, ellagic acid, and astragalin, as well as quercetin-3-glucoside, was also determined in the infusions of the freeze-dried flowers of Filipendula vulgaris [15], coinciding with the results of the present study in the higher concentration of quercetin-3-glucoside. It is significant that each compound isolated from a particular part of the Filipendula plant has specific biological activities associated with it [10]. Another study involving the flowers, in addition to the phenolics mentioned above, confirmed the presence of kaempferol [16]. Mass spectrometry was used in two papers, the first of which positively identified 11 phenolic compounds, and tentatively identified other related substances [17], confirming seven of the compounds identified in the present work. The second paper concluded that the quantitative distribution of the compounds identified in the extracts depended on the extraction solvent applied, but in general, the highest efficiency corresponded to the methanolic extract [18], in which a total of 18 polyphenolic compounds and derivatives were determined, four of them coinciding with those determined in this work (gallic acid, catechin, ellagic acid, and astragalin). However, to the authors’ knowledge, the presence of other polyphenols, such as hydroxybenzoic acids or procyanidins, has never been reported in flower extracts. 3-hydroxybenzoic acid is used in cosmetics as a skin conditioning agent, while 4-hydroxybenzoic acid has properties as a fragrance and preservative agent (data obtained from PubChem). As for the procyanidin oligomers determined in the present work, they have been investigated as potential hair growth-promoting agents [31].

In summary, F. vulgaris contains a wide range of polyphenols with health benefits and, consequently, extracts derived from the plant can be considered a promising source of ingredients for use in cosmetics based on natural ingredients and marketed under the organic cosmetics label.