| المستخلص: |
This study aimed to optimize the antimicrobial efficacy of plant extracts for control of foodborne pathogenic and spoilage microorganisms using food model media based on meat and milk. The extracts of 7 medicinal plants (Gambooge, Clove, Marjoram, Galangal, Thyme, Cinnamon and Marigold) were screened for their antimicrobial activities against nine standard microbial strains (S. aureus, B. cereus, L. monocytogenes, E. coli, P. aeruginosae, S. enterica, C. albicans, Rhizopus sp and A. flavus). All alcoholic extracts (except that of Marigold) inhibited all tested microorganisms. Gambooge extracts showed the best activity against all tested microorganisms producing the widest inhibition zones ranged from 13 to 40 and 8 to 25 mm against bacteria and fungi respectively, followed by Clove extracts with inhibition zones ranged from 11 to 33 and 8 to 22 mm respectively. The most susceptible bacteria among Gram-positives to the tested plant extracts were Bacillus cereus, while the least susceptible were L. monocytogenes. The most susceptible bacteria among Gram-negative bacteria were Salmonella enterica while the least susceptible were P. aeruginosa. on the other hand fungal strains showed the highest resistance more than all tested bacteria and yeast. aqueous extracts showed less activity than alcoholic extracts. When the methanolic extracts were mixed into food models the antimicrobial activity were reduced and the required minimum inhibitory concentrations (MICs) were duplicated. MICs of Gambooge extract ranged from 0.234 to 3.750, 0.468 to 6.666 and 0.877 to 7.5 mg/ml when tested on microbiological (control) media, meat model and milk model respectively. The antimicrobial activity was reduced on semi-skimmed milk model more than that on meat model and control media respectively. The results indicated that plant extracts possessing antimicrobial activity can be exploited as ideal food preservatives after taken into account the reaction and interaction between food components and extract.
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