Evaluation of Chemical Composition, Sun Protection Factor and Antioxidant Activity of Lithuanian Propolis and Its Plant Precursors

Abstract

The growing interest in polyphenols of natural origin and their plant sources encourages the study of their chemical composition and biological activity. Propolis is widely used as a source of phenolic compounds. The aim of this study is to evaluate and compare the chemical composition, antioxidant activity and sun protection factor (SPF) of the ethanolic extracts of the poplar buds, birch buds and pine buds of propolis plant precursors collected in Lithuania. The IC50 concentration of the extracts was evaluated using DPPH and ABTS methods. Extracts of poplar buds, birch buds and propolis showed a lower IC50 concentration by ABTS and DPPH methods compared with pine buds extracts. Poplar buds and propolis extracts showed the highest SPF value, while birch and pine buds extracts showed a lower SPF value. High-performance liquid chromatography (HPLC) analysis results showed that phenolic acids, such as p-coumaric acid and cinnamic acid, and flavonoids, such as pinobanksin and pinocembrin, were identified in all the tested extracts. Salicin has been identified only in poplar buds extracts. The results of antioxidant activity showed that propolis poplar and birch buds are a promising source of biologically active polyphenols.

Keywords: UV protection; antioxidant activity; birch; extract; pine; poplar; propolis.

Figure 1

Physical appearance of poplar (1), birch (2), pine (3) buds and propolis (4) extracts.

Figure 2

Chromatogram of A—birch buds, B—poplar buds, C—propolis and D—pine buds extracts. 1—salicin, 2—neochlorogenic acid, 3—chlorogenic acid, 4—vanillic acid, 5—caffeic acid, 6—vanillin, 7—P-coumaric acid, 8—ferulic acid, 9—cinnamic acid, 10—quercetin, 11—pinobanksin, 12—apigenin, 13—kaempferol, 14—pinocembrin.

Figure 3

Antioxidant activity of poplar, birch, pine buds and propolis extracts. Subgraph (A)—ABTS inhibition % of extracts (1 µg CAE/mL to 100 µg CAE/mL); subgraph (B)—DPPH inhibition % of extracts (1 µg CAE/mL to 100 µg CAE/mL); subgraph (C)—IC50_ABTS concentration; subgraph (D)—IC50_DPPH concentration. Subscripts of different letters indicate statistically significant differences between subjects (p < 0.05).

Figure 4

SPF values of poplar, birch, pine buds and propolis extracts by spectrophotometric method. Results are presented at extract concentrations of 10 µg CAE/mL, standards of quercetin, p-coumaric acid and salicin at 10 µg/mL. Subscripts of different letters symbolize a statistically significant difference between samples (p < 0.05).