Investigation of the functional groups of bioactive compounds, radical scavenging potential, antimicrobial activity of Trigonella foenum aqueous extract “in vitro”

Herbs and spices, which are essential part of the human diet, have been used in traditional medicine to increase the flavor, color, and aroma of various foods and food products. Herbs and spices are also known as preservative, antioxidative, and antimicrobial agents. Plant extracts and their components with pathogen-growth suppression effect and little toxicity to host cells could be considered as excellent candidates for developing new antimicrobial agents. Trigonella foenum- graceum is an annual herbaceous plant with bright yellow and sometimes purple-white flowers. Therapeutic effects of this plant include analgesia, anti-cancer, and treatment of diabetes by lowering blood sugar and lowering blood lipids. In ancient Egypt, this plant was used to embalm the dead and incense. The seeds of the plant are used to treat leprosy, hemorrhoids, and relieve bronchitis. The seeds of this plant contain various compounds such as vitamins, amino acids, saponins, fatty acids, and flavonoids. The antimicrobial and antioxidant effects of T. foenum have been detrmined byvarious studies. This study was therefore aimed to produce the T. foenum extract and evaluate its antioxidant and antimicrobial properties. 

Fifty g of powdered plant was added to 250 mL of water and stirred for 72 h. The solution was passed through the Whatman filter paper and then centrifuged at 3000 rpm for 10 min to discard the suspended solids. Next, a vacuum evaporator was used to remove the excess water and the obtained extract was packed and kept away from light at 4 °C. Total phenol and flavonoid contents were measured by colorimetric methods. The antimicrobial effect of the extract on Escherichia coli, Enterobacter aerogenes, Staphylococcus aureus, Bacillus cereus and Candida albicans was evaluated using disc diffusion agar (DDA), well diffusion agar (WDA), minimum inhibitory concentration (MIC) and minimum bactericidal /fungicidal concentration (MBC/MFC) methods. Interaction of aqueous extract and Chloramphenicol and Amphotericin B was also evaluated. Antioxidant effect of the extract was determined by ABTS, DPPH, and β-carotene/linoleic acid bleaching assay. Fourier-transform infrared spectroscopy (FTIR) was also used to identify the functional groups. 

Total phenol and flavonoid contents of the extract were 46.60 mg GAE/g and 37.57 mg QE/g, respectively. The aqueous extract also showed antioxidant effects of 60.55, 55.53 and 50.40%, based on DPPH, ABTS methods and β-carotene/linoleic acid assay, respectively. T. foenum aqueous extract had the inhibitory effect on all examined microorganisms, at all concentrations (20, 40, 60 and 80 mg/mL). The antibiotic effect of chloramphenicol for E. coli, E. aerogenes, S. aureus and B. cereus was 13.30, 14.50, 18 and 19.10 mm, respectively, and the effect of this antibiotic for C. albicans was not measured. Also, the antibiotic effect of amphotericin B for C. albicans was 15.10 mm. Furthermore, the interaction of T. foenum aqueous extract with the antibiotic chloramphenicol presented a synergistic effect on the examined bacteria and led to a significant increase in inhibition zone diameter. Additionally, the interaction of the extract with antibiotics showed a synergistic effect on C. albicans. In infrared spectrum, peaks at 3370, 2965, and 1613 cm-1 were related to stretching vibration of O-H, C-H, C=C bonds of aromatic ring and aromatic groups of T. foenum aqueous extract. In general, the extract of T. foenum could be used as a natural antioxidant and antimicrobial agent in food and pharmaceutical industries.