Characterization of the Chemical Composition and Biological Activities of Bog Bilberry (Vaccinium uliginosum L.) Leaf Extracts Obtained via Various Extraction Techniques

This investigation aimed to assess the chemical composition and biological activities of bog bilberry (Vaccinium uliginosum L.) leaves. Hydroethanolic extracts were obtained using four extraction techniques: one conventional (CE) and three alternative methods; ultrasound (UAE), microwave (MAE) and high-pressure (HPE) extractions. Spectrophotometric analysis was conducted to determine their chemical content, including the total phenolic content (TPC) and total flavonoid content (TFC). Furthermore, their antioxidative and antimicrobial properties were evaluated. HPLC (high performance liquid chromatography) analysis identified and quantified 17 phenolic compounds, with chlorogenic acid being the predominant compound, with the lowest level (37.36 +/- 0.06 mg/g) for the bog bilberry leaf extract obtained by CE and the highest levels (e.g., HPE = 44.47 +/- 0.08 mg/g) for the bog bilberry leaf extracts obtained by the alternative methods. Extracts obtained by HPE, UAE and MAE presented TPC values (135.75 +/- 2.86 mg GAE/g; 130.52 +/- 1.99 mg GAE/g; 119.23 +/- 1.79 mg GAE/g) higher than those obtained by the CE method (113.07 +/- 0.98 mg GAE/g). Regarding the TFC values, similar to TPC, the highest levels were registered in the extracts obtained by alternative methods (HPE = 43.16 +/- 0.12 mg QE/g; MAE = 39.79 +/- 0.41 mg QE/g and UAE = 33.89 +/- 0.35 mg QE/g), while the CE extract registered the lowest level, 31.47 +/- 0.28 mg QE/g. In the case of DPPH (1,1-diphenyl-2-picrylhydrazyl) antioxidant activity, the extracts from HPE, UAE and MAE exhibited the strongest radical scavenging capacities of 71.14%, 63.13% and 60.84%, respectively, whereas the CE extract registered only 55.37%. According to Microbiology Reader LogPhase 600 (BioTek), a common MIC value of 8.88 mg/mL was registered for all types of extracts against Staphylococcus aureus (Gram-positive bacteria) and Salmonella enterica (Gram-negative bacteria). Moreover, the alternative extraction methods (UAE, HPE) effectively inhibited the growth of Candida parapsilosis, in comparison to the lack of inhibition from the CE method. This study provides valuable insights into bog bilberry leaf extracts, reporting a comprehensive evaluation of their chemical composition and associated biological activities, with alternative extraction methods presenting greater potential for the recovery of phenolic compounds with increased biological activities than the conventional method.