Comparative composition, antioxidants, and antimicrobial effects of 3- and 7-day fermented seeds of <i>Nigella sativa</i>

Abstract

The significance of fermentation is gaining more relevance due to the need for better preparation of plants, the desire for better plant  constituents, and the aim for the preservation of medicinal plants. Hence, this study sets out to determine and compare the pH,  proximate composition, chemical constituents, antioxidant, and antimicrobial effects of 3-day and 7-day fermented seeds of Nigella sativa.  The fermentation of the seed was done for 3 and 7 days using 2.5% sugar. The pH of the sample declined from 3.5 to 3.45 during  the fermentation. The proximate composition (moisture, ash, lipid, protein, and carbohydrates) was higher for the 3-day fermented sample while fiber was higher for the 7-day sample. The phytochemical constituents (tannins, saponins, phenols, alkaloids, flavonoids,  phytates, oxalates, terpenoids, steroids, and glycosides) were higher for the 3-day than the 7-day sample. The Gas Chromatography-Mass  spectrometry technique showed peaks that were characterized as 17 and 20 constituents on days 3 and 7 of the sample,  respectively. The antioxidant capacity (ranging from 35.50% to 82.69% for the 3-day and from 37.50% to 84.99% for the 7-day sample)  varies by the increasing concentration (7.81 mg/mL to 1000 mg/mL) of the sample. The diameter of zones of inhibition tested at different  concentrations (25 mg/mL, 50 mg/mL, and 100 mg/mL) showed varying degrees of activity against Proteus vulgaris and Staphylococcus  aureus. The zones obtained were higher 8-10 mg/mL against Staphylococcus aureus and 10-12 mg/mL against Proteus vulgaris for the 7-day fermented sample while 8.0 to 9.0 mg/mL was obtained for the 3-day fermented against Staphylococcus aureus and 8.0 to 10.0 mg/mL against Proteus vulgaris. Overall, the results of this study indicated that fermentation contributed to enhancing the bioactive components and antioxidant capacity of the fermented seeds of N. sativa thereby supporting the use of fermentation in the production of valueadded functional foods.