Earlier, Boligon et al. [15], using the HPLC-DAD method, had analyzed the qualitative composition of phenolic acids in crude extracts from purchased leaves of N. officinale grown in special hydroponic systems in Santa Maria in Brazil. Only caffeic and chlorogenic acids were found to be present in those extracts. Our HPLC-DAD analyses of parent plant extracts also detected caffeic acid, but chlorogenic acid was absent. In addition to caffeic acid, our extracts proved to contain six other phenolic acids (Table 5) [15]. Aires et al. [42] performed qualitative and quantitative phenolic acid estimations in methanol: water (v/v) extracts from young baby-leaves of N. officinale grown by organic farmers in the northern region of Portugal. The study revealed the presence of five phenolic acids: caffeic, chlorogenic, dicaffeoyltartaric and gallic acids. The main compounds were: dicaffeoyltartaric acid (5.50 mg/100 g DW) and chlorogenic acid (3.30 mg/100 g DW), which were not found in the herb extracts in our study (Table 5). The amounts of caffeic acid (0.20 mg/100 g DW) and gallic acid (1.60 mg/100 g DW) were respectively about 35.5 and 8.5 times lower in comparison with our results (Table 5). In another study, carried out by Zeb [43], seven phenolic acids were identified: caffeoylmalic, caftaric, p-coumaric, gallic, p-hydroxybenzoic, sinapic and vanillic, and also derivatives of coumaric, p-coumaric, ferulic and gallic acids in methanol: water (60%:40%) extracts from the leaves of wild N. officinale plants found in Pakistan. By comparison, our herb extracts also contained p-coumaric acid and gallic acid, but we did not confirm the presence of caftaric, p-hydroxybenzoic, sinapic and vanillic acids. In our study, we did not test for caffeoylmalic acid (Table 5) [43].
A study conducted by Taveira et al. [44] dealt with estimation of phenolic acids in biomass extracts from other species of the Brassicaceae family—Brassica oleracea L. var. costata DC. The study involved a qualitative analysis of phenolic acids in crude aqueous extracts from the biomass of shoot cultures grown on an MS medium agar containing 20 g/L sucrose and 2 mg/L BA, 0.1 mg/L NAA, and 0.5 µM gibberellic acid (GA). The composition of phenolic acids in those cultures differed from the composition of our N. officinale microshoot cultures. The acids identified in those extracts were chlorogenic acid and its derivatives such as: 4-acylchlorogenic, 3-caffeoylquinic, 3-p-coumarylquinic, 3-ferulylquinic and quinic acids [44]. Production of phenolic acids by in vitro cultures was also the subject of our earlier studies [45]. We had analyzed qualitative and quantitative composition of phenolic acids in extracts from S. chinensis cv. Sadova agar and agitated microshoot cultures grown on the MS medium with different PGRs of different concentrations. In methanolic extracts from these cultures we estimated eight phenolic acids: chlorogenic, cryptochlorogenic, gallic, neochlorogenic, protocatechuic, salicylic, syringic and vanillic acids. Similarly, the amounts of individual compounds and the total amount of phenolic acids depended on the type of in vitro culture and the variants of the applied media. The maximum total amount of phenolic acids in extracts from S. chinensis cv. Sadova agar microshoot cultures (357.93 mg/100 g DW) had been obtained by us for the cultures maintained on the MS medium containing 2 mg/L BA and 0.5 mg/L NAA, collected after 30 days of culture, and this amount was 1.5-fold higher than the maximum total content determined for the N. officinale agar microshoot cultures (237.52 mg/100 g DW) (Table 2). In extracts from agitated microshoot cultures of S. chinensis cv. Sadova, the maximum total content of phenolic acids (269.73 mg/100 g DW) was confirmed for extracts of the biomass cultured in the MS medium with 2 mg/L BA and 2 mg/L NAA over a 30-day growth period, and it was similar to the maximum total content determined in the N. officinale agitated microshoot cultures (236.74 mg/100 g DW) (Table 3) [45]. Quantitative differences in terms of phenolic acid yields were also found among the agitated shoot cultures of three cultivars of St John’s-wort—Hypericum perforatum cvs. Elixir, Helos, and Topas, cultured on variants of the MS medium differing in the composition of PGRs and their concentrations [46]. Extracts of all three cultivars were proved to produce the same phenolic acids: chlorogenic, 3,4-dihydroxyphenylacetic, p-coumaric, neo-chlorogenic, protocatechuic and syringic acids. However, the amounts of individual compounds and the total amount of phenolic acids depended on the cultivar studied and the applied media variants. The cultivar ‘Helos’, which had been grown on the MS medium containing 0.1 mg/L BA and 0.1 mg/L NAA for three-week culture cycles, was the richest source of phenolic acids [46]. The maximum total amount of phenolic acids in extracts from H. perforatum cv. ‘Helos’ agitated microshoot cultures (220.63 mg/100 g DW) was similar to the content in extracts from our N. officinale agitated microshoot cultures (236.74 mg/100 g DW). However, there were also differences in the concentrations of PGRs at which the maximum total amount of these compounds was obtained (Table 3) [46]. write only the main points
- Different studies have analyzed the qualitative composition of phenolic acids in extracts from different plant species
- N. officinale extracts contained caffeic acid, but not chlorogenic acid
- Other studies found different phenolic acids in N. officinale extracts, including dicaffeoyltartaric and gallic acids
- Studies on other plant species in the Brassicaceae family and St. John's-wort identified different phenolic acids in their extracts
- The composition and amount of phenolic acids in extracts varied depending on the plant species, in vitro culture conditions, and growth media used