Antimicrobial activity of spices against Escherichia coli O157:H7 and their application in solid and liquid foods

Twenty-three spices were evaluated for their antimicrobial activity against Escherichia coli O157:H7. Garlic, cinnamon, clove, oregano and sage (0.5%--10%) reduced E. coli O157:H7 from 1.0 to 9.0 log cfu/ml in MacConkey Sorbitol Agar (MSA). The growth of E. coli O157:H7 in ground beef was limited 2.1 log cfu/g by clove at 37°C for 24 hr at 7.5% level. Oregano and sage did not have significant effect on E. coli O157:H7 in ground beef. In salami fermentation, E. coli O157:H7 was significantly reduced from 5.0 log cfu/g to 3.7 log cfu/g by garlic and clove treatment at 1%.; Garlic (1.5%) and heating showed synergistic effect against E. coli O157:H7 in ground beef patties during cooking from 51°C to 72°C. Ground beef patties with garlic (1.5%) stored at 25°C and 4°C had more than 90% and 60% lower E. coli O157:H7, respectively after cooking. Among five different agars used to recover heat-treated E. coli O157:H7 in meat the effectiveness in decreasing order was non-selective Tryptic Soy Agar (TSA), 202 Agar overlaid with TSA, MSA overlaid with TSA, 202 agar and MSA agar. Selective agar (202 and MSA) overlaid with TSA is called Thin Agar Layer method (TAL) developed in our laboratory to effectively recover injured cells. The 202 agar is a new agar developed to differentiate E. coli O157:H7 from E. coli.; Cinnamon (0.1%, 0.2% and 0.3%) alone and with sodium benzoate or potassium sorbate (0.025%, 0.05%, 0.075% and 0.1%) exhibited antimicrobial effect against E. coli O157:H7 in apple juice during storage at 8°C and 25°C. Synergistic effect increased with the increase in the amount of cinnamon and preservatives. Sodium benzoate alone or with cinnamon exhibited greater antimicrobial activity against E. coli O157:H7 compared to potassium sorbate.; The minimum inhibitory concentration against E. coli O157:H7 in agar dilution method of essential oil of oregano, cinnamon, clove, sage and garlic was 300-ppm, 350-ppm, 750-ppm, 1750-ppm and 3000-ppm, respectively. Oregano essential oil was the most inhibitory and garlic was the least inhibitory against E. coli O157:H7 (oregano ≥ cinnamon > clove >> sage >> garlic).