Comparative Study Regarding the Chemical Composition and Biological Activity of Pine (Pinus nigra and P. sylvestris) Bark Extracts

Abstract

The bark resulted after the industrial processing of wood represents a byproduct of the forestry industry, used in many suboptimal ways, being considered a natural waste. Currently, it has been highlighted that the bark of different woody plants may be an important source of several bioactive compounds, with various beneficial biological functions. The aim of this study is to evaluate and compare the chemical composition and biological activities of two different pine species (Pinus nigra and Pinus sylvestris) bark extracts. Ultrasound (UAE) and microwave (MAE) assisted extractions were performed in order to obtain the extracts. The total polyphenol (TPC) and total tannin (TTC) contents of the extracts were assessed via the Folin–Ciocâlteu method. The volatile and polyphenolic compounds were identified and quantified via a GC/MS analysis and an UPLC-PDA analysis, respectively. The antioxidant activity (AOA) was evaluated using the DPPH and ABTS assays, while the antibacterial activity was assessed using the minimum inhibitory concentration (MIC) protocol. The results showed that the Pinus sylvestris bark extracts obtained by UAE had a higher TPC, TTC and AOA, while the Pinus nigra bark extracts obtained by MAE had higher volatile compounds content (mainly α-pinene and β-pinene). Moreover, the inhibition of the bacterial growth was more efficient in the case of Pinus sylvestris extracts, Gram-positive bacteria being the most affected, while Gram-negative strains presented a relative resistance to the tested extract concentrations. These results may indicate the potential use of the pine bark extracts as antioxidant or antibacterial agents.

Phytochemical Profile and Biological Effects of Spruce (Picea abies) Bark Subjected to Ultrasound Assisted and Microwave-Assisted Extractions

“…The discrepancy between our results and the data found in literature might be due to the different methodologies used for extraction, or even because the vegetal matrices used in the baseline studies were not barks. For example, in one of our previous works conducted on pine bark, it was also shown that the UAE is more efficient for extracting polyphenols and for achieving extracts with higher antioxidant capacities [ 61 ].…”

“…For assessing the TPC, the Folin–Ciocâlteu method was used [ 66 ], slightly modified as previously mentioned in one of our studies [ 61 ]. Briefly, 40 µL of diluted (1:5) extract were brought together in a vial with distilled water, Folin–Ciocâlteu reagent and a 20% Na 2 CO 3 solution.…”

“…The tannins absorbance was translated into TTC expressed as mg pyrogallol/g vegetal material by using pyrogallol as an external standard. The exact work protocol was previously described [ 61 ], but this study used a 1:50 extract dilution and a 15% Na 2 CO 3 solution.…”

“…The identified compounds were quantified based on their peak height. The detailed analysis protocol was previously described [ 61 ].…”

“…The compounds associated with each peak were then quantified based on the peak area and identified based on the similarity of UV spectra when compared to standard solutions. This method was also described in our previous study [ 61 ].…”