Plants are a valuable source of biologically active molecules, mainly phenolic compounds. In the present study, the total phenolic content (TPC), DPPH· and ABTS+ scavenging activity as well as ferric reducing ability (FRAP) of aqueous ethanolic (70%) extracts of Cistus incanus L. and Asarum europaeum L. herb, Geum urbanum L. rhizome, Angelica archangelica L. root, white mulberry (Morus alba L.), lemon balm (Melisa officinalis L.), red raspberry (Rubus idaeus L.) and Betula pendula Roth. leaves were determined. In addition, the phenolic profiles of the studied plant extracts and antibacterial activity have been investigated. The extracts from C. incanus and G. urbanum demonstrated the highest TPC and antioxidant capacity, while the extracts from A. archangelica and white mulberry were characterized by the lowest values. A remarkable correlation was also found between the TPC and antioxidant activity of the examined extracts. HPLC analysis showed that the studied extracts were sources of both phenolic acids and flavonoids. More flavonoids than phenolic acids were identified in the extracts of C. incanus, M. alba, R. idaeus and B. pendula compared to the other extracts tested. Not all extracts showed a significant impact on the growth of the tested bacterial strains. Escherichia coli was the most sensitive strain to lemon balm extract (MIC, 0.125 mg/mL), whereas the strains of Acinetobacter baumannii and Bordetella bronchiseptica were sensitive to the G. urbanum extract (MIC, 0.125 mg/mL). Among Gram-positive bacteria, Enterococcus faecalis was the most sensitive to G. urbanum extract. In turn, Staphylococcus aureus and Staphylococcus epidermidis were sensitive to the extracts from C. incanus herb (MIC, 0.125 mg/mL), red raspberry (MIC, 0.125 mg/mL) and lemon balm leaves (MIC. 0.25 mg/mL). Based on the obtained results, the applicability of the studied plant extracts as additives to food and cosmetic products may be considered in the future.
Plant material is a source of many value components, such as phenolic compounds, which may scavenge free radicals and thus reduce oxidative stress. Phenolic compounds showing antioxidant properties include flavonoids, phenolic acids, lignans and stilbenes. The properties of the aforementioned compounds are used by plants as a defense mechanism against the adverse effects of UV radiation, temperature and mechanical damage. They also act as an important chemical defense against herbivores through their specific physiological action on insects. In addition, by reacting directly with the oxidation products of fatty acids, phenolic compounds can prevent adverse changes from occurring in both living organisms and food. They prevent the deterioration of the organoleptic and sensory characteristics of food products. Phenolic compounds also exhibit antimicrobial activity, causing the inhibition of microbial growth by interfering with the transport of nutrients that are important to their function. The functional groups present in phenolic compounds enable their building into the lipid membranes of microorganisms, causing changes in their permeability and reducing resistance to abiotic factors. This action may often be enhanced or weakened due to the possibility of both synergistic or antagonistic effects between phenolic compounds and their interaction with other components present in the plant material. The content of phenolic compounds in plant material may be influenced by both the cultivation system of plants and the method of harvesting and obtaining raw material, as well as the method of drying and storing it. The way in which the biologically active compounds are extracted from a plant material and the part of the plant used and its belonging to a specific botanical family are also important.
Nowadays, consumers are increasingly choosing products of natural origin or those that contain natural substitutes for synthetic additives. When reading the label, they pay attention to information about the presence of plant extracts derived from commercially available plant material, which is often used in natural medicine or culinary applications. In the current study, plant material that is popular with consumers due to its availability and recommended biological properties was used. Cistus incanus L. belonging to the Cistaceae family has been used in folk medicine for the treatment of diarrhea and fever and as an anti-inflammatory agent in skin diseases, rheumatism and nephritis. The herb and leaves of C. incanus exhibit antimicrobial, antiviral and antioxidant properties. Their aqueous solutions are a source of phenolic compounds, particularly flavonoids, phenolic acids and ellagitannins. Asarum europaeum L., known as European wild ginger (Aristolochiaceae), is cultivated in Poland as an ornamental and useful plant. The herbal raw materials are shoots and roots, which emit a characteristic spicy odor and are used in the production of medicines that are used to treat respiratory diseases and in veterinary medicine. Geum urbanum L. (Rosaceae), on the other hand, is used in folk medicine for gastrointestinal and liver diseases and externally to reduce gingivitis. Its roots and rhizomes are a source of tannins, mainly ellagitannins, essential oils, flavonoids and triterpenes. Angelica archangelica L. (Apiaceae), a valuable medicinal plant that has been partially protected in Poland since 2014, is characterized by its peculiar and pleasant fragrance. The stems and seeds are used in confectionery and in the preparation of liqueurs, and the leaves and roots for medicinal purposes, especially in digestive problems, anorexia, migraine or menstrual and obstetric complaints. The roots are a source of coumarins, a flavonoid called archangelenone, palmitic acid and sugar. White mulberry (Morus alba L., Moraceae family) grows as a shrub; the leaves are mainly used in China to feed silkworms, whereas in Poland, after drying, they are packaged and sold as herbal teas. They are recommended as preparations for decreasing blood glucose and reducing obesity, and they show antibacterial, anti-inflammatory and antioxidant activities. Flavonoids and phenolic acids play a key role in antioxidant activity. In contrast, extracts of lemon balm (Mellisa officinalis L.) are a source of rosmarinic acid, which has documented antioxidant activity, as well as flavonoids and essential oils. Lemon balm belongs to the Lamiaceae family, which in traditional medicine is used in the treatment of many diseases in different cultures, for example, to alleviate gastrointestinal and hepatic problems. It has sedative properties, so drinking an infusion of lemon balm leaves before bed accelerates sleep and is recommended for people with irritable bowel syndrome. Fruits and leaves of Rubus idaeus L. (Rosaceae) are valuable medicinal raw materials with nutritional and dietary values. They are used as a cold remedy, rich in mucilaginous compounds, pectin, macro- and micronutrients and ellagic acid. Leaves can be included in herbal mixtures with diuretic and choleretic effects. On the other hand, Betula pendula leaves belonging to the Betulaceae family are purchased for their diuretic and diaphoretic properties. They are excellent for urinary tract problems and strengthening the body after an infection. Phenolic compounds, mainly flavonoids, usually predominate in the chemical composition of extracts prepared from birch leaves using a 20% ethanol solution and methanol.
Obtaining extracts from the plant material in question with the use of ethanol (70%) and a preliminary assessment of their biological activity may be the basis for their future use, e.g., in food, to protect it against the harmful effects of external factors and thus have a positive effect on the human body, reducing the risk of certain diseases. The main purpose of this study was to obtain aqueous ethanolic extracts from the selected plant material available on the Polish market belonging to seven botanical families and to determine their antioxidants and antimicrobials. The content of phenolic compounds and their types were also determined using HPLC, especially with regard to phenolic acids and flavonoids.
The dried herb of Cistus incanus L. and Asarum europaeum L., rhizome of Geum urbanum L., root of Angelica archangelica L., leaves of white mulberry (Morus alba L.), lemon balm (Melisa officinalis L.), red raspberry (Rubus idaeus L.) and Betula pendula Roth. bought from an herbal shop in Warsaw, Poland, were used as the plant material. Folin–Ciocalteu’s phenol reagent, 2,2-diphenyl-1-picrylhydrazyl (DPPH·), gallic acid, 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox), 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), and 2,4,6-tri(2-pyridyl)-s-triazine (TPTZ) were bought from Sigma-Aldrich (Poznań, Poland). High performance liquid chromatography (HPLC) standards were purchased from Sigma Life Science (Merck, Darmstadt, Germany) and ChromaDex® (Irvine, CA, USA), respectively. Other chemicals and solvents were of analytical grade and were used as received without further purification. They were obtained from Avantor Performance Materials (Gliwice, Poland).
The microorganisms used in this study were obtained from the collection of the Department of Pharmaceutical Microbiology, Medical University of Warsaw (Warsaw, Poland). They belonged to Gram-positive bacteria: Staphylococcus aureus ATCC 6538P, Staphylococcus aureus ATCC 25923, Staphylococcus epidermidis ATCC 12228, Enterococcus faecalis ATCC 29212, Enterococcus faecium ATCC 6057, Bacillus subtilis ATCC 6633, Geobacillus stearothermophilis ATCC 7953 and Gram-negative bacteria: Escherichia coli ATCC 25922, Klebsiella pneumoniae ATCC 13883, Proteus vulgaris ATCC 13315, Proteus mirabilis ATCC 12453, Listeria monocytogenes 1043S, Serratia marcescens ATTC 13880, Enterobacter cloacae DSM 6234, Pseudomonas aeruginosa ATCC 27853, Stenotrophomonas maltophilia ATCC 12714, Bordetella bronchiseptica ATCC 4617, Acinetobacter baumannii ATCC 19606.
The aqueous ethanolic extracts from the investigated plant material were performed with 70% ethanol, as described previously, with a minor alteration. For this purpose, 20 g of each plant material and 250 mL of aqueous ethanol were placed in a flask and stirred using a water bath for 10 h at 45 °C. The plant residues were then separated by filtration through a Whatman No. 1 paper filter and the ethanol was evaporated under vacuum on a rotary evaporator at 40 °C (Rotavapor R-200, Büchi Labortechnik, Flavil, Switzerland). The resulting extracts were lyophilized (Alpha 1-4 LSCplus, Osterode am Harz, Germany) and stored at −20 °C until further analysis. The extraction yield was evaluated on the basis of the mas
