Evaluation of Total Phenolic, Flavonoid Contents, Antioxidant Activities and Antibacterial Activities of Nigella sativa Seed Meal Extracts

Abstract

Nigella sativa seed has been used as a food ingredient and a medicinal for a long time in powder, oil, or extract form. This research aimed to determine the total phenolic content, total flavonoid content, antioxidant activity, and antibacterial activity of Nigella sativa seed meal, a by-product of cold-pressed oil extraction plant. The seed meals were extracted by the Soxhlet apparatus using ethanol and aqueous as solvents. The extracts were investigated for total phenolic content with the Folin-Ciocalteu reagent using gallic acid as a standard (y = 0.0065x + 0.0489, R² = 0.9976). The total flavonoid content was determined by the aluminum chloride colorimetric assay using quercetin as a standard (y = 0.0013x + 0.1237, R² = 0.9988). The efficiency of an antioxidant activity was considered from the DPPH radical scavenging. The antibacterial activity was evaluated against Bacillus cereus, Staphylococcus aureus, and Escherichia coli by agar well diffusion method at 1,000 mg/mL. It was found that the TPC and TFC values of the ethanolic extract were 7.96±0.71 mg GAE/g DW and 7.15±2.75 mg QE/g DW, respectively, which were higher than an aqueous extract. The ethanolic and aqueous extracts also exhibited antioxidant activity with IC50 values of 1.39 and 1.68 mg/mL, respectively. These extracts were effective against all tested microorganisms in the range of 1.00±0.00 to 10.33±0.58 mm. The results showed that Nigella sativa seed meal still contains the active compounds that can be further studied for utilization.