Antimicrobial activity of essential oils from herbs and spices and application of black cumin to Rainbow trout fillets

This research was conducted for two purposes. In the first study, The antimicrobial activity of selected herb and spice essential oils for control of growth and survival of microorganisms was examined. Inhibition of growth was determined by the paper disc agar diffusion method. Antibiotic susceptibility discs were used as control. Minimum lethal concentration (MLC) was determined by the tube dilution method. Essential oils from anise, angelica, basil, carrot, celery, cardamom, coriander, dill weed, fennel, oregano, parsley, and rosemary were evaluated. Inhibition ranged from complete with oregano to no inhibition with carrot oil for each of the test strains which included: Listeria monocytogenes, Staphylococcus aureus, Escherichia coli 0:157:H7, Yersinia enterocolitica, Pseudomonas aeruginosa, Lactobacillus plantarum, Aspergillus niger, Geotrichum, and Rhodotorula. Oregano essential oil showed the greatest inhibition (zone ³70-80 mm) (MLC ~ 8 ppm). Coriander and basil were also highly inhibitory (MLC = 25 - 50 ppm) to E. coli O: 157:H7 and other bacteria tested. Pseudomonas was the most resistant microorganism to the spice oils but still had a MLC in the 100 to 200 ppm range using oregano, basil and coriander oils. Anise oil was not particularly inhibitory to bacteria (inhibition zone ~ 25 mm), however anise oil was highly inhibitory to molds. Basil, coriander, and oregano were also highly inhibitory to the fungi assayed.

In the second study, the effectiveness of aqueous, ethanolic and petroleum ether extracts of black cumin (Nigella sativa) for control of growth and survival of common spoilage and pathogenic microorganisms was investigated. More over, the applications of black cumin oil on fresh Rainbow trout fillet were tested. In vitro, the ethanolic extract of black cumin seed was found to be highly inhibitory (zone = 35-55 mm) against Listeria monocytogenes, Staphylococcus aureus, Yersinia enterocolitica, and Rhodotorula, moderately inhibitory (zone =16-28mm) against Escherichia coli 0:157:H7, Salmonella typhimurium, Pseudomonas aeruginosa, Lactobacillus plantarum, and Geotrichum, and only weakly or not inhibitory (zone<12 mm) against Aspergillus niger by the paper disc agar diffusion method. Freshly harvested rainbow trout fillets were stored at 0°C (on ice) and at 4°C using five marinate treatments. Treatments evaluated were a plain teriyaki marinate (control), and four marinates containing black cumin and/or dimethyl dicarbonate (DMDC). Trout treated with marinate using black cumin oil had significantly lower aerobic plate counts (< 3 log), coliform counts, Listeria and yeasts and mold counts (p < 0.05). DMDC marinated trout was not significantly differ than control marinate for all counts (p < 0.05). Fresh trout treated with either ground seeds or the combination of black cumin oil and DMDC marinate exhibited moderate reduction (>1 log) in all counts (p < 0.05). Since a marinate containing black cumin essential oil was highly inhibitory to both spoilage and pathogenic microorganisms and also significantly (p<0.0001) increased shelf-life by almost two weeks, it may be useful for extending shelf life of fresh refrigerated fish.