Evaluation of Total Phenolic, Flavonoid Contents, and Antioxidant Activities of Seed Extracted from Coriander (Coriandrum sativum L.) and Black Cumin (Nigella sativa) Spices

Black cumin (Nigella sativa) and coriander (Coriandrum sativum L.) are common culinary spices that are used singly or combined in the diet of many populations of Ethiopia, and there is a long-held belief of their health-enhancing properties. The present study was designed to investigate the antioxidant properties, phenolic and flavonoid contents of aqueous methanolic extracts from Nigella sativa and Coriandrum sativum L. seed samples. The contents of polyphenols and flavonoids were evaluated by colorimetric method, and antioxidant activity was determined based on the ability to scavenge free radicals by using DPPH assay. An aqueous methanol extract of Coriandrum sativum L. resulted in the highest phenolic content from West Dembia (1.799 +/- 0.0011 mg GAE/g), followed by Nigella sativa from East and West Dembia (1.737 +/- 0.0014 & 1.734 +/- 0.0013 mg gallic acid equivalent per gram (mg GAE/g) respectively) and Coriandrum sativum L. from West Dembia (1.678 +/- 0.0018 mg GAE/g) measured by the Folin-Ciocalteu reagent method. The greatest flavonoid content was observed with extracts of Coriandrum sativum L. (1.114 +/- 0.0005 mg quercetin equivalents per gram samples (mg QE/g)) from East Dembia district followed by Nigella sativa (1.002 +/- 0.0007 (mg QE/g)) as measured by an aluminum chloride colorimetric method, while the least was recorded for Coriandrum sativum L. (0.926 +/- 0.0013 mg QE/g) and Nigella sativa (0.764 +/- 0.0010 mg QE/g) from West Dembia district. Among the two selected spice extracts, Nigella sativa from East Dembia district displayed the highest DPPH radical scavenging activity with an IC50 value 432-mg ascorbic acid equivalent per gram sample (AAE/g), while Nigella sativa and Coriandrum sativum L. from West Dembia and Coriandrum sativum L. (East Dembia) showed lower antioxidant activities having 372, 320, and 366 mg AAE/g of sample respectively. These results confirmed that Nigella sativa and Coriandrum sativum L. extracts possess appreciable natural antioxidant potentials, thereby providing good justification for their increased domestication and combined food consumption.