Ripening-Dependent Antimicrobial Activity of African Nightshade Berry Extracts: Implications for Food Preservation and Pharmacology
Keywords:
African nightshade, Extract, Antimicrobial Activity, BerriesAbstract
Evidence of bioactive compounds in African nightshade (Solanum nigrum Complex) edible berries necessitated an investigation into the antimicrobial activity of edible berry extracts from four African nightshade (Solanum nigrum complex) varieties at different stages of ripening. Ethanolic extracts were prepared from Black NS, Giant NS, JKUAT Improved, and KALRO Agriculture varieties harvested at green, colour break, ripe, and senescence stages. The extracts were tested against Gram-positive bacteria (Staphylococcus aureus and Bacillus cereus), Gram-negative bacteria (Escherichia coli and Salmonella typhi), and fungi (Candida albicans and Aspergillus niger) using the hole-plate diffusion method, while minimum inhibitory concentration (MIC) assays were used to determine extract potency. Results showed that antimicrobial activity varied significantly with variety, ripening stage, and microorganism type. Black NS and KALRO Agriculture varieties demonstrated the highest inhibitory effects, particularly at the green and colour break stages. Gram-positive bacteria were more susceptible to the extracts than Gram-negative bacteria, with S. aureus recording the greatest sensitivity. Fungal species exhibited the least susceptibility, requiring higher concentrations for inhibition. Antimicrobial potency decreased progressively with ripening, likely due to reductions in bioactive compounds such as phenolics, tannins, flavonoids, and alkaloids. MIC values ranged from 6.25–12.50 µg/mL for most bacterial species, while fungal inhibition required concentrations of 100 µg/mL. The findings demonstrate that African nightshade berries possess significant natural antimicrobial properties and could serve as potential sources of plant-based preservatives and medicinal ingredients for the food and pharmaceutical industries.
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