The Effect of Excipients on the Flavonoid Content in Tilia cordata L. Extracts

Introduction. Tilia cordata L. flowers are a valuable source of phenolic compounds, particularly flavonoids, which demonstrate significant antioxidant, anti-inflammatory, and respiratory-relief activities [1,2]. The extraction efficiency of these bioactive compounds can be substantially affected by the presence of excipients, which influence their solubility and stability. This study aimed to evaluate the impact of selected excipients on the total flavonoid content in Tilia cordata L. flower extracts. Materials and methods. Tilia cordata L. blossom extracts were prepared from 0.5  0.001 g of dried material (Suppliers A and B) in 10 mL of 70% ethanol. Reflux extraction was conducted for 1 h with or without 1% α- or β-cyclodextrin. Flavonoid content was determined by the aluminium chloride colorimetric method and expressed as quercetin equivalents (mg RE/g). Antioxidant activity was evaluated using the DPPH assay and expressed as Trolox equivalents (mg TRE/g). Absorbance was measured spectrophotometrically in triplicate. Results and discussion. The total flavonoid content in Tilia cordata L. flower extracts without excipients was 0.491  0.02 mg RE/g (Supplier B) and 0.507  0.01 mg RE/g (Supplier A). After adding excipients, a significant increase was observed. Using α-cyclodextrin, the total flavonoid content rose to 4.875  0.01 mg RE/g (Supplier A) and 5.072  0.01 mg RE/g (Supplier B). When β-cyclodextrin was applied, the flavonoid content reached 5.111  0.02 (the same results were obtained for supplier A and B) mg RE/g. Antioxidant activity determined in the samples were 841.79  1.24 (Supplier A) and 976.25  0.03 (Supplier B) mg TRE/g (without excipients). Using α-cyclodextrin, the antioxidant activity increased to 916.17 ± 0.03 mg TRE/g (Supplier A) and 997.71 ± 0.02 mg TRE/g (Supplier B). The use of β-cyclodextrin also increased the antioxidant activity in the samples to 961.23 ± 1.45 (Supplier A) and 996.28 ± 1.24 (Supplier B) mg TRE/g. Flavonoid content strongly correlated with antioxidant activity. The enhancement likely resulted from improved solubilization, stabilisation, and mass transfer of flavonoids, as well as reduced degradation during extraction. Among the tested excipients, β-cyclodextrin produced the greatest effect, consistent with its ability to form inclusion complexes with polyphenols and enhance their solubility. Conclusions. The study confirmed that the addition of excipients during reflux extraction significantly increased the total flavonoid content in Tilia cordata L. flower extracts 9-10 times more. A parallel enhancement was observed in antioxidant activity, where DPPH values increased about 1.2 times more. Among the tested excipients, β-cyclodextrin exhibited the strongest effect. The strong correlation between flavonoid concentration and antioxidant capacity indicates that excipient-assisted extraction improves both chemical yield, and functional activity of herbal extracts.