Acta Pharm. 50 (2000) 195-207
Twenty samples of Nigella sativa seeds collected from different localities in Egypt were investigated. Bacterial counts contaminating the seeds ranged from 12.0 to 3.9 × 106 CFU g-1. According to the morphological shape, sixty-nine different bacterial isolates were obtained. The seeds were exposed to increasing doses of gamma radiation. A dose of 7.0 kGy was found sufficient to eliminate all bacteria from the tested seeds. Three radioresistant bacterial strains, which were isolated at a dose level higher than 3.0 kGy, were identified as Bacillus cereus, Micrococcus luteus and Bacillus sphaericus. Their D10 values were 1.0, 1.4 and 1.4 kGy, respectively. Statistical analysis showed a significant difference in the bacterial counts of seeds stored in sealed and unsealed bags. The tested seeds required a relative humidity lower than 85% for safe storage. Fixed oil from the seeds had a greater effect on the growth of isolated bacterial strains than volatile oil. The fixed oil exerted higher antibacterial activity against Gram-positive bacteria such as Staphylococcus aureus and B. cereus than against Gram-negative bacteria. Data analysis showed that there is no significant difference in the relative percent of fixed oil extracted from the control and irradiated samples. Gamma irradiation does not affect the main constituents of N. sativa fixed oil.
Keywords: Nigella sativa seeds, bacterial contamination, gamma radiation, radioresistant strains, oil composition