Determination of the antioxidant and antimicrobial activities and total phenolic content of Borago officinalis L. leaf extracts prepared by ultrasound-assisted extraction

This study investigated the antioxidant, total phenolic, and antimicrobial properties of Borago officinalis L. leaves, a medicinal plant widely used in complementary medicine and as an edible wild plant. Ethanolic, methanolic, and aqueous extracts were prepared from washed and unwashed leaves using ultrasound-assisted extraction. Antioxidant activity was determined by the CUPRAC and ABTS assays, total phenolic content by the Folin–Ciocalteu method, and antimicrobial activity by agar well diffusion and broth microdilution methods. The minimum inhibitory concentration, minimum bactericidal concentration, and minimum fungicidal concentration values were also determined. The total phenolic contents (mg GAE/g dw) of methanolic, ethanolic, and aqueous extracts were 475.22, 294.32, and 1039.87, respectively, for washed leaves, and 460.27, 188.06, and 1038.43, respectively, for unwashed leaves. CUPRAC values (mmol TE/g dw) were 1.465, 0.586, and 4.233 for washed leaves and 1.350, 0.298, and 3.207 for unwashed leaves, respectively, whereas ABTS values (mmol TE/g dw) were 6.547, 3.551, and 25.205 for washed leaves and 6.520, 4.371, and 22.473 for unwashed leaves, respectively. The ethanolic extract of unwashed leaves produced inhibition zones against Acinetobacter baumannii (7.18 mm) and Escherichia coli (8.59 mm). In the broth microdilution assay, the ethanolic extract of unwashed leaves and the ethanolic and methanolic extracts of washed leaves exhibited MIC values of 0.196–1.563 mg/mL against all tested microorganisms, whereas aqueous extracts showed MIC values of 0.098–1.563 mg/mL (washed leaves) and 0.049–6.25 mg/mL (unwashed leaves). Overall, aqueous extracts exhibited the highest total phenolic contents and antioxidant capacities. These findings demonstrate that Borago officinalis leaves are a promising natural source of antioxidant and antimicrobial compounds with potential applications in the food, cosmetic, and phytotherapeutic industries.